You are hereCannabis Plant Problems & Symptoms | Marijuana Nutrient Deficiencies
Cannabis Plant Problems & Symptoms | Marijuana Nutrient Deficiencies
Many weed plant problems can be fixed by getting a good nutrient system that is formulated for plants like the tomato. The key thing is that the nutrients need to come with a different nutrient schedule for the "vegetative" and "flowering" stage, just like marijuana plants.
And remember that maintaining a proper pH will prevent a bunch of nutrient deficiencies, because the roots can only access the nutrients if the pH is in the correct range.
How do I check the pH and how's it related to marijuana nutrient deficiencies anyway?
If you're growing in soil, aim for a root pH between 6.5 - 7.0. In hydroponic marijuana grows (including growing in inert mediums like coco coir), aim for a root pH between 5.5-6.5.
View pictures and descriptions below of all the common marijuana nutrient deficiencies and other weed plant problems.
Boron Deficiency
Problem: Cannabis leaves and roots show abnormal and slowed growth when showing a boron defiency. The first signs of a cannabis boron deficiency is abnormal or thick growth tips. New leaves may display chlorosis (yellowing of leaves). Stems may become rough or hollow. The plant may look like it has a calcium deficiency because boron is needed for the plant to properly use calcium. New growth is affected the most, and may look like it's been burnt or scorched.
Solution: Boron is not absorbed will without enough potassium and nitrogen, or if there isn't enough moisture. You plant may also exhibit signs of a boron deficiency if the pH is too high or low. Flush your system with clean, pH'd water that contains about half the nutrients needed for the plant and watch to make sure that the problem clears up for new growth.
Calcium Deficiency
Problem: Signs of a cannabis calcium deficiency can be hard to pin down since calcium deficiencies are often accompanied by magnesium, iron, and other deficiencies. However, some of the major signs of a calcium deficiency are in the leaves which will display dead spots, crinkling, spotting, or small brown spots. Another sign of a cannabis calcium deficiency is new leaves will appear small and distorted with curled tips The insides of the plant and well as the flowers/buds may show signs of decay. Roots may show signs of bacteria and may be dying off or be under developed.
Solution: If the pH of your root zone is off, then your cannabis cannot properly absorb calcium through its roots so the first step is to ensure that you have the correct pH for your growth medium. Learn more about pH and cannabis. Different strains of cannabis tend to have different nutrient problems, but calcium, magnesium, and iron deficiencies often appear together in cannabis. Therefore many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case this common deficiency appears. I have listed some available Cal-Mag supplements that I have used along below with some general information about each one. After supplementing with Cal-Mag and correcting the pH, you should expect to see new healthy growth within a week.
Botanicare Cal-Mag Plus is a calcium, magnesium, and iron plant nutrient supplement. General application is to mix 1 tsp (5ml) of Cal-Mag into each gallon of water. I have used Cal-Mag Plus several times with great results.
Guaranteed Analysis: Nitrogen (N) 2.0%, Calcium (Ca) 3.2%, Magnesium (Mg) 1.2%, Iron (Fe) 0.1%
Derived from: Calcium Nitrate, Magnesium Nitrate, Iron EDTA
Dolomite Lime
If you're looking for something that can be used in your organic setup, I highly recommend a product called "Dolomite Lime." Dolomite is a good source of calcium and magnesium and can be mixed with your soil. The great thing about dolomite is it works slowly over the course of a few months. Dolomite has a neutral pH of about 7.0 and will help keep soil at the correct neutral pH range which is optimum for cannabis growth. You can buy Dolomite Lime online, but with shipping it's almost always waaaay cheaper to pick up a bag at a home improvement or gardening store such as Lowes, Home Depot, gardening centers, etc. If possible, try to get a finer grade of dolomite compared to something that is more coarse.
How to Use Dolomite Lime for Cannabis: When growing cannabis indoors, add 6-7 teaspoons of fine dolomite lime to each gallon's worth of soil. So if you're mixing enough soil to fill a 5 gallon container, you want to add 30-35 teaspoons (about 2/3 cup) of dolomite lime to the mix. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with water that has been pH'ed to 6.5. After getting the soil wet, mix the soil well and wait a day or two to let the soil settle before checking the pH and adding plants. When growing in an outdoor garden, follow the dolomite lime manufacturers instructions.
Copper Deficiency
Problem: A cannabis copper deficiency manifests itself as leaves curling back, lack of growth, and unusual coloring of the leaves. New young leaves may be dark and twisted, while other leaves may start showing signs of yellow or white. It is very unlikely that there is no copper available in your water or soil. Copper deficiencies generally crop up when there is a pH problem, so that the cannabis can't get to the copper even though it's there.
Solution: Flush your system with clean, pH'd water that contains about half the correct amount of nutrients needed by the plant. Watch to make sure that the problem starts to clear up within a couple of days.
Heat and Light Stress
Problem: Your cannabis plant can only withstand a certain amount of heat and light. After a certain point, your cannabis will start exhibiting signs of stress on the leaves near the sources of light and/or heat. Your leaves will get yellow or brown brown spotting and may appear generally burnt in places when there's too much light.
If you directly touch a plant's leaves with the lights, you will also leave "burns" if the bulbs were hot when they touched the leaves.
When the heat gets too high, the edges of the serrated leaves will begin to curl up even if there are no burns or other signs of light stress.
Light Burn
Heat Stress
Solution: Find a way to lower the temperature and/or increase the circulation in the grow room or grow area if heat is the problem. Having a small fan blowing over the tops of your plants will help prevent hot spots from forming directly under your grow lights.
If your marijuana plants are just getting too much light, try removing some of the lights or moving your lights further away from the tops of the plants.
When learning how to weed, it's best to try to keep things at a comfortable room temperature at all times for optimal growth. If it's too hot for you, it's probably too hot for your plants.
Iron Deficiency
Problem: An iron deficiency manifests itself as yellowing of the leaves although the veins will tend to stay green. It looks similar to a magnesium deficiency, but will only affect younger leaves.
Solution: Iron deficiencies are very uncommon as long as the pH is kept below 6.5 (5.7 for hydroponic or rockwool). Too much Phosphorus can also lock up iron. The best thing you can do is check the pH of your system, and then flush the system with clean pH'd water that contains nutrients at half strength to start, then start working your way up to full nutrient strength. It's worthwhile to note that iron has a tendency to react with many other components of fertilizer solutions and can cause other nutrients to be locked up from the plant. When supplementing your plant with iron, it is often necessary to not use fertilizer for that watering. If you are supplementing with iron, make sure you first read the label of both the fertilizer and the iron supplement you are using to minimize any problems.
Magnesium Deficiency
Problem: The edges of the leaves may become yellow or bright green and may start feeling crispy to the touch. The light green or yellow coloring may also effect the veins of the leaves.
Solution: It is very important to maintain a proper pH in order to avoid a magnesium deficiency. Adding more magnesium to a system when there is a pH lock-out will only make the situation worse because the plant will not be able to absorb any magnesium until the pH has been corrected. Flush the system with properly pH'ed water that contains a full set of proper nutrients and see if the new growth starts looking healthier.
Manganese Deficiency
Problem: Leaves may become yellow in between the veins, with mottled brown spots on the affected leaves. These brown dead patches may spread and eventually kill the leaf. Leaves may also shred and fall apart.
Overall growth of the marijuana plant may be stunted.
Solution: Manganese deficiencies are often caused by a pH that is too high, or if the plant is getting too much iron.
If you have a manganese deficiency in soil, try to correct pH to 6.0 - 6.5l. In hydro, correct pH to 5.5 - 6.0. You are looking to avoid higher pH ranges, as this is where manganese deficiencies are most likely to occur.
Flush your system with clean, pH'd water that contains about half the correct amount of nutrients needed by the plant. Watch to make sure that the problem starts to clear up within a couple of days.
Molybdenum Deficiency
Problem: The initial symptoms may appear similar to a nitrogen deficiency (yellowing of older, lower leaves). Leaves may become mottled or spotted. However, the tell-tale sign of a molybdenum deficiency is the leaves may start to display a unique orange, red or pink color around the edges which will start to move toward the center of the leaf. Sometimes the color appears in the middle of the leaves as opposed to the edges.
Solution: Flush your system with clean, pH'd water that contains about half the correct amount of nutrients needed by the plant. Watch to make sure that the problem starts to clear up within a couple of days. Molybdenum gets locked out at lower pH ranges. Molybdenum may get locked out in soil that has a pH of lower than 6.5. With hydro or soil-less mediums, molybdenum may be locked out at pH ranges of 5.5-6.0 and lower. Try to keep the pH of your growing medium above these ranges to help prevent a molybdenum deficiency.
Nitrogen Deficiency
Problem: A nitrogen deficiency will cause the older, lower leaves on your plant to start turning yellow and eventually die. It's relatively normal for your plant's leaves to start turning yellow towards the end of your flowering cycle as the plant becomes nitrogen deficient while it's creating its buds.
However, if you notice your leaves turning yellow in the vegetative stage or in the beginning parts of the flowering stage, your plant may be experiencing a nitrogen deficiency which will need to be treated. The first picture is a plant in the vegetative stage which is experiencing the beginnings of a nitrogen deficiency. The second plant is showing signs of nitrogen deficiency late in flowering and is completely normal. The last picture is an infographic about nitrogen and your marijuana plant.
Solution: You can find many pre-mixed nutrients from the store which contain nitrogen or you could use nitrate of soda or organic fertilizer which are both good sources of nitrogen. Try supplementing your regular nutrients with a bit more nitrogen and see if the plant starts recovering.
More About Nitrogen and Your Marijuana Plants
Nitrogen is especially important during the vegetative stage of your cannabis plants. As your plants start flowering, they will need lower amounts of nitrogen.
Nitrogen is one of the 3 nutrients that is included in almost every kind of plant food.
When looking at plant nutrients, you'll almost always see 3 numbers listed, like 3-12-6 or 5-10-5. These numbers represent the percentage of Nitrogen (N), Phosphorous (P) and Potassium (K) contained in the bottle. Just about all plant life on Earth needs these 3 elements to grow.
The very first number, "3" in the case of the picture to the right, always displays the proportion of nitrogen in this nutrient bottle compared to the other 2 nutrients (Phosphorus and Potassium respectively).
The reason nitrogen is in all plant nutrient formulations is because it's vital to plant processes.
Note: During the last few weeks before harvest, marijuana plants starts pulling all the remaining nitrogen from her leaves as part of the bud-making process. This causes yellowing leaves starting towards the bottom of the plant. This is part of the natural flowering process and you don't need to fight it.You may notice that marijuana leaves are yellowing in almost all pictures of marijuana plants with big buds that are close to harvest. You tend to get smaller yields from nitrogen-toxic plants with dark green leaves at harvest.
Remember: It's Normal For Marijuana Leaves To Start Turning Yellow As Harvest Time Approaches
Nitrogen Toxicity
Problem: Dark green leaves, weak stems, and overall slow growth. Marijuana leaves that are nitrogen toxic often get "The Claw" or talon-like leaves that are bent at the ends. The also do a weird curving / cupping that is often mistaken for overwatering, but is unique to nitrogen toxicity. You can see a picture of this leaf "clawing" below.
Leaves that turn into claws often start turning yellow and dying if the nitogen toxicity is not treated, much like a nitrogen deficiency, only the leaves will continue to get more and more clawed. Leaves eventually turn yellow or brown and fall off. You can tell if yellowing is caused by too much nitrogen because the rest of the plant will be dark green, and the yellowing leaves will turn into claws first.
Different strains react differently to nitrogen toxicity. Some plants get dark green leaves with no clawing. Some strains will get leaves that do the weird 90 degree bend at the tips, while other strains or individual plants start curling like claws and then turn yellow / brown and fall off like a deficiency. Yet these are all signs of too much nitrogen.
Signs of Nitrogen Toxicity
- Dark green leaves and foliage
- Leaf tips may turn down, without signs of overwatering.
- You may notice yellowing on the affected leaves or other signs of nutrient deficiencies as time goes on
- Nitrogen toxicity is often but not always accompanied by nutrient burn
- The Claw often seems random, affecting leaves here and there
- Heat and pH problems will make the clawing worse, as they stress out the plant and lower her defenses
- As time goes on, the claw leaves will eventually start turning yellow, getting spots, and dying
Solution: Reduce the Nitrogen your plant is getting!
Reduce the amount of nitrogen that is being fed to the plants. If you are feeding extra nutrients, cut down. If you are in the flowering / budding stage, make sure you're using a formula that's specifically meant for flowering, or else it will have too much nitrogen.
If you are not feeding extra nutrients, you may have "hot" soil that has been supplementing with extra nutrients. In that case, flush your plants with filtered, pH'ed water to help leech out the extra nitrogen.
Effected leaves likely won't recover, but you should stop seeing the problem spread to more parts of the plant.
Wait! I'm not sure if it's a Nitrogen toxicity!
Ok, you ruled out overwatering, now what?
When I first got started growing, everyone kept telling me that this particular kind of leaf clawing was caused by under or overwatering my plants, pH problems, or heat problems.
Yet in my case, I knew that it wasn't over or under watering (I was growing in hydro, where roots grow directly in water and air stones are constantly adding oxygen). I knew it wasn't pH (my reservoir water had the right pH) and I knew it wasn't heat since the grow area was slightly cooler than room temperature.
So then what was really causing my claw leaves?
It's understandable that other growers were mistaken. It is true that many stresses will make any other problem worse.
Plus overwatering can cause a similar kind of leaf clawing (learn more below). And if you do have nitrogen toxicity, than heat or pH problems will make the problem much worse as your plant is too weak to fight back.
Now, you may or may not know that marijuana (or any plant) needs an element known as "Nitrogen" to grow.
In fact, nitrogen is one of the 3 nutrients that is included in almost every kind of plant food.
When looking at plant nutrients, you'll almost always see 3 numbers listed, like 3-12-6 or 5-10-5. These numbers represent the percentage of Nitrogen (N), Phosphorous (P) and Potassium (K) contained in the bottle. Just about all plant life on Earth needs these 3 elements to grow.
The very first number, "3" in the case of the picture to the right, always displays the proportion of nitrogen in this nutrient bottle compared to the other 2 nutrients (Phosphorus and Potassium respectively).
The reason nitrogen is in all plant nutrient formulations is because it's vital to plant processes.
For marijuana plants, when they don't get enough nitrogen, the bottom leaves start turning yellow and dying. Left unchecked, a nitrogen deficiency can cause the the whole plant to eventually die.
What I'm here to talk to you about today is the opposite, nitrogen toxicity, or too much nitrogen.
Why You Should Treat And Prevent Nitrogen Toxicity
- Marijuana plants that get too much Nitrogen in the vegetative stage don't grow as vigorously.
- Too much nitrogen is especially harmful in the flowering stage, because this will cause your plant to produce smaller buds.
- If you react quickly and reduce your nitrogen levels at the first sign of toxicity, your plant will quickly recover.
Note: Some strains with the word "Claw" in the name tend to do The Claw more easily than others.
Problems with excess nitrogen are not common in the wild, it's a lot more common to see nitrogen toxicity on indoor plants, especially when overzealous growers go overboard with nutrients.
Occasionally you'll come across a strain or particular plant that likes lower levels of nutrients, and when this happens, it's important to realize the plant is showing signs of toxicity, even if all the other plants in your garden seem fine.
One of the most common signs off too-many-nutrients is "nutrient burn," or when the tips of your leaf appear brown or burned. Yet there are specific signals your plant will display when she's getting too much nitrogen...
How You Know You Have a Nitrogen Toxicity
- Dark green leaves and foliage
- Leaf tips turn down, without signs of overwatering.
- You may notice yellowing on the affected leaves or other signs of nutrient deficiencies as time goes on
- Nitrogen toxicity is often but not always accompanied by nutrient burn
- The Claw often seems random, affecting leaves here and there
- Heat and pH problems will make the clawing worse, as they stress out the plant and lower her defenses
- As time goes on, the claw leaves will eventually start turning yellow, getting spots, and dying
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The distance between the leaves to the lights or irregular light patterns from reflectors often seem to affect the condition, which is why many growers believe that light is somehow causing the problem.
- You may notice this clawing first appears on dark green leaves that aren't getting enough light (they aren't able to use up all their nitrogen and become nitrogen toxic).
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If you use vegetative plant nutrients during the flowering stage, then they'll deliver too much nitrogen. This is why you need to get special nutrients meant for the blooming / flowering stage. You'll notice that flowering nutrients always contain a smaller percentage of nitrogen (the first number) compared to nutrients for the vegetative stage. Learn more about marijuana nutrients here.
- Many growers mistakenly keep raising nutrient levels or adding additional nitrogen when they see yellow leaves in the flowering stage, not realizing that it's natural for plant leaves to start yellowing as harvest approaches. Adding too much nitrogen in the flowering stage can cause nitrogen toxicity even when you can see yellow lower leaves
Note: During the last few weeks before harvest, marijuana plants starts pulling all the remaining nitrogen from her leaves as part of the bud-making process. This causes yellowing leaves starting towards the bottom of the plant. This is part of the natural flowering process and you don't need to fight it.You may notice that marijuana leaves are yellowing in almost all pictures of marijuana plants with big buds that are close to harvest. You tend to get smaller yields from nitrogen-toxic plants with dark green leaves at harvest.
It's Normal For Marijuana Leaves To Start Turning Yellow As Harvest Time Approaches, Don't Keep Adding More Nitrogen!
I know a lot of marijuana plant problems can look similar, but now that you're armed with the right information, you'll know exactly what to do if you see Nitrogen Toxicity affecting your marijuana plants.
Nutrient Burn
Problem: You may notice the tips of your plants showing signs of nutrient burn. If it only seems to be affecting the tips, then there's no need to worry, but if you start noticing the problem spread to the whole leaf, then you should immediately do something to treat your plant before there's more damage. Nutrient burn can also manifest itself as random spots around the edges of the leaves, or with leaf tips curling downwards.
Solution: Flush your system with plain, pH'ed water. Give your plants some time to recover, and start them with a fraction of the nutrients you were giving them before working your way up to more nutrients. Many nutrients come with instructions to feed your plant more nutrients than most plants actually need. It's good business for them if you use more nutrients. However, in my experience it's a good idea to view the feeding charts that come with nutrients as the maximum amount of nutrients and actually start with much less.
Over watering
Problem: Your plants leaves will start drooping if they've been over-watered or under-watered. If you've overwatered your plant, its leaves will be firm and curled down all the way to the stem of the leaf. You may also notice Chlorosis (Leaf Yellowing).
Plants use their roots to get oxygen which is dissolved in water or oxygen in their grow medium. When you overwater a plant, its roots are sitting in stagnant water which no longer has any oxygen left. The reason your plants droop is because basically their roots are starving for oxygen.
Overwatered Marijuana Plants
- Drooping / Curling is the first sign of overwaterd marijuana plants
- Leaves are firm and curled down all the way from the stem to the leaf
- Will eventually lead to leaf yellowing and other signs of nutrient problems if not corrected
Solution: The best thing you can do for overwatered plants is give them time without watering, and then start off watering slowly until things seem back to normal.
Learn how to water your marijuana plants.
If plant medium seems to stay wet, you may need better drainage. Make sure that water drains freely from the bottom of your container (it's recommended that you provide enough water to get at least 20% extra runoff every time you water your plants). You should see water coming out the bottom within a minute or two after watering. Then don't water your plants again until the soil is dry up to your first knuckle.
If your plants are already overwatered, you can try to increase the temperature and airflow to help the water evaporate more quickly. You can also use a pencil to gently poke some air holes into the growing medium to provide extra aeration and oxygen to the roots.
For soil grows, you generally only want to water the plant when the soil feels dry if you press a finger in it. You can also use the "lift the pot" method to decide when to water your plants (basically wait until your pot feels "light" since the plants have used up all the water). For other growing mediums besides soil, your watering method will vary, but if your plants are drooping and you've been feeding them a lot of water, it's a good idea to cut back and see if that helps.
If you're growing hydroponically with your marijuana roots directly in water and you see the signs of overwatering, that means you have a problem at your roots. Either your plants have root rot which is preventing them from getting oxygen at their roots, or you are not dissolving enough oxygen into the water (you can easily increase the dissolved oxygen in your water with a quality air pump and a few air stones).
Need more help?
If your plant is experiencing "the claw" and not just normal drooping (the ends of leaves are curling like a claw or pointing down like talons), then you may actually have a nitrogen toxicity (too much nitrogen).
These Plants Are NOT Overwaterd, These Leaves Show Signs of
Nitrogen Toxicity
("The Claw", tips bent down, curling / clawing, dark green leaves)
Phosphorus Deficiency
Problem: Phosphorus aids in root growth and overall health of the plant and is especially essential when the plant is in flowering. Cannabis loves phosphorus and it is very unlikely that cannabis gets too much phosphorus. A plant which is deficient in phosphorus will have slow, stunted growth. If there is a major deficiency, the leaves may exhibit dark gray or purplish splotches. The last picture below is an info-graphic with more information about phosphorus and your marijuana plant.
Solution: Check the pH and flush system. An excess of Fe and Zn may cause a phosphorus deficiency. If you've tried everything else, then you may try adding a bit more phosphorus to your feeding schedule and see if that helps clear up the problem. Cannabis plants love phosphorus, and therefore it is unlikely that you will give your cannabis too much phosphorus.
Potassium Deficiency
Problem: Older leaves turn yellow then start getting dark, scorched lesions around the edges of the leaves. Plants may stretch and stems may become weak. The symptoms are very similar to an iron deficiency except the tips of the leaves curl as the edges burn and die. The last picture below has some more information about the potassium requirements of your marijuana plant.
Solution: Potassium isn't absorbed properly when there is too much calcium or nitrogen in the system. Check the pH of your water, and flush your whole system with water that contains half the normal amount of nutrients and see if your plant starts showing signs of improvement.
Root Rot
Marijuana Root Rot & Root Slime
Problem: Roots need water, but if they are exposed to water with bacteria they will start to rot. Roots that have been drowning in too much water without enough available oxygen are much more susceptable to problems. Healthy roots are white to cream-colored while roots affected by root rot are brownish and actually smell like they're rotting. Plants affected by root rot will spontaneously start losing their leaves, yellowing, drooping, and otherwise look like they're dying. You will also notice that affected plants will start drinking less water. If you notice these symptoms in your plant, then it can't hurt to try all the suggestions for stopping root rot.
It's important to notes that root damage is permanent. A recovering plant will be able to make new growth, but it's old infected roots will likely never recover. Root rot mostly affects hydroponic systems, but can also result from over watering your plants in soil or other medium. Basically anytime the roots are sitting in water, they are at risk of devloping root rot.
- Plants may appear overwatered or droopy
- Brown, slimey, smelly roots
- Plant leaves often start turning yellow
- Leaves start dying and falling off rapidly
- Plants drink much less water than usual
Solution: It can be tough to get rid of root rot and many people feel it's easier to just scrap the plant and start over. However, there are proven techniques that will cure your plant of root rot problems. In order to get rid of root rot successfully, you need to take a two pronged approach. You will need to treat the plant's root directly and you will also need change the plant's environment so that root rot no longer has a good place to grow.
If you don't fix the environmental causes of root rot, then it will just keep coming back no matter what you do. Therefore, it's important to go through the below list and make sure you're covering all your bases to prevent a re-occurrence. It's also important to note that affected roots will likely never recover, just like how discolored leaves on the plant will never recover. What you're looking for is new, healthy white root growth.
Aquashield is also much cheaper than most other similar root treatments,
In addition to treating root rot, Aquashield also works as a preventative, even in hot, unclean reservoirs. Since I first started using Aquashield in DWC, bubbleponics, and other hydroponics, it has successfully preventing me from getting root rot as long as I keep using it. I also use it when growing in soil if I suspect root problems.
How to prevent and treat root rot:
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You will need to keep your grow area as clean as possible at all times to stop bacteria before it starts. Before you begin your grow, you should also thoroughly clean all grow-related items with white vinegar and water to kill all bacteria.
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Some people like to add beneficial bacteria to their water to help prevent and treat root-related plant diseases and help make nutrients available to the plant. Some of the formulas available are Piranha, Aquashield, VooDoo Juice, Great White (Great White has great reviews, yet is obscenely expensive), Subculture B, Rooters, and Plant Savers. Most of these can be used with both hydro and soil grows. I personally recommend Aquashield because I've used it successfully to treat Root Rot (and by 'successul' I mean new white roots exploded out of the old mushy brown ones and I was able to eventually harvest the buds).
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If you have a hydroponic system, it's best to change your reservoir water regularly in order to prevent any one type of bacteria from overgrowing the whole reservoir. I personally recommend trying to change your water at least once a week. Regularly changing your water will also help your plants get better access to nutrients and the roots of the plant love that 10-15 minutes where they get access to the oxygen in the air (just don't ever let the roots get dry).
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It is beneficial to try to get as much oxygen as possible dissolved in your water. Therefore it's a good idea to buy a BIG air pump and big air stones for your hydroponic system. Root rot cannot thrive in an oxygen rich environment and your plant's roots love it.
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Ensure that the temperature of the water never gets warmer than a comfortable room temperature. Warm water holds much less dissolved oxygen than colder water and also provides the perfect environment for bacteria to grow. The maximum recommended temperature for the water in your reservoir is around 72°F (22°C). Trying to maintain water temps around 65°F - 68°F (18°C - 20°C) seems to be optimal for both plant growth and root rot prevention.
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In a hydroponic system, ensure that any dead roots, dead leaves or other types of plant debris doesn't get into the reservoir because they will provide a breeding ground for bad bacteria as they start rotting.
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Don't let any light get to your roots or reservoir water ever, as it provides heat and light which will promote the growth of bacteria.
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SM-90 is another supplement that some growers use to prevent and treat root rot, as well as help your plant's overall root health. It's made up of a few different types of oils that happen to kill many pathogens as well as make nutrients more available to your plant's roots. I also like to have SM-90 around because it will kill aphids, spider mites, and white powdery mold when used as a foliar spray. I personally feel that anyone who grows marijuana should have some SM-90 around. I've heard that SM-90 will kill beneficial bacteria, so I don't use it if I'm adding Aquashield. I always use one or the other.
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Some people recommend treating root rot with H2O2, also known as hydrogen peroxide. While adding hydrogen peroxide to your water will kill all bacteria including root rot, it is only effective in your system for 1-2 days since the H2O2 is quickly converted to oxygen and water. Therefore, if you use hydrogen peroxide as a treatment for root rot, you will need to treat your water daily to prevent re-occurances. If you want to kill all the bacteria in your water, I personally recommend getting SM-90 instead because it will remain effective in your water for at least a week. If you want to encourage good bacteria to grow, then don't either use SM-90 or hydrogen peroxide and get Aquashield instead.
Your plant can completely recover from root rot as long as you catch the problem early enough, so it's important to stay vigilent of root rot during your first couple of grows, expecially when growing with hydroponics.
Sulfur Deficiency
Problem: A sulfur deficiency will manifest itself as all-over chlorosis (yellowing of leaves) starting with the oldest leaves and may look like a nitrogen deficiency at first. The parts that are underneath the leaves may take on a distinctive pinkish red or orange color. The buds on a flowering plant may start dying off. Unlike other deficiencies that cause chlorosis, a sulfur deficiency will start at the back of the leaf and move it's way forward as opposed to started at the tips. Leaves become stiff and brittle and will eventually fall off.
Solution: Check and correct your pH to make sure that your sulfur isn't being locked out. Sulfur moves slowly through the plant so it may take a few days after you fix the problem before you start noticing an improvement in your plant.
Under-watering
Problem: If your plant is drooping and you're sure you haven't overwatered it, than it might need more water. If you've been underwatering your plant, its leaves will look limp and lifeless.
Solution: While it can be good to let your plant dry out a bit after watering, you should always water the plant again before it's leaves start drooping. A good way to tell if a potted plant is ready to be watered is to pick it up and tell if it feels heavy or not. As plants use up all the water in their pot, it will start to get lighter. If you need something for comparison, you can get an extra pot and fill it with your growing medium. Now you can use this extra container for comparison with your potted plants as it represents the 'dry weight' of your growing medium. If you pick up a potted plant and its feels just slightly heavier than your dry pot, then you know it's time to water your plant. After a while you get a feel for how heavy your plants need to be and you may not even need the extra pot anymore.
Click here to see a time-lapse of an under-watered marijuana plant coming back to life.
1 picture taken every 75 minutes. Strain is Island Sweet Skunk. Used with permission.
Zinc Deficiency
Problem: Younger leaves start yellowing in between the veins. Leaf tips get discolored and start dying. the leaves will take a unique banded appearance and the plant will stop growing vertically. There will be much less space between new nodes which will cause all the new leaves to start bunching together. If the plant is budding, it's flowers may start dying.
Solution: Flush your system with clean, pH'd water that contains about half the nutrients needed for the plant (including zinc, iron, and manganese). Watch to make sure that the problem starts to clear up on new growth within a couple of days.
ǂ Cannabis Bugs, Mold & Other Marijuana Pests
Unfortunately, bugs or pests can totally mess up your marijuana harvest.
Some bugs live in soil, while other pests are airborne. Mold can be a big problem too. But you don't have to sit back and take it.
This page aims to be a comprehensive resource on the different types of bugs / pests / mold that can affect your marijuana crop, along with tips for preventing and solving each problem.
Pests that can affect your marijuana plants include aphids, spider mites, ants, whiteflies, white powdery mildew / white powdery mold, stem rot, and even mammals such as gophers and rats.
It's time to fight back against bugs, mold and pests!
If you have anything that you would like added, please contact me!
Most pests can be erradicated with SM-90.
Mist your plants in a solution made of 1 part SM-90, 5 parts water.
When you spray the plants, make sure you get the undersides of the leaves.
You'll want to do this when the lights are about to go off(or else the leaves will get burned). You can get a sprayer like this one on amazon.com, or at Home Depot for about $12.
Diseases of Cannabis are caused by organisms or abiotic sources.
Organisms include fungi (first and foremost), nematodes, parasitic plants, bacteria, and viruses.
Abiotic (non-living) causes include nutrient deficiencies, pollutants and genetic diseases. Different diseases prevail in different crops (e.g., drug cultivars versus fiber cultivars). Disease prevalence is also modulated by geography and climate.
The claim that Cannabis has no diseases is not correct, Cannabis suffers over 100 diseases, but less than a dozen are serious.
Serious diseases include gray mold, hemp canker, damping off, assorted leaf spots, blights, stem cankers, root rots, nematode diseases, broomrape, macro- and micronutrient deficiencies, and genetic diseases.
Environmentally stressed plants become predisposed to diseases. Stress includes drought, insufficient light, untoward temperatures, or growing plants in monoculture.
(McPartland, J. M., 1996. A review of Cannabis diseases. Journal of the International Hemp Association 3(1): 19-23.)
That quote was taken from a great page on Cannabis diseases <http://www.hempfood.com/IHA/iha03111.html> that everyone should read.
Aphids
Aphids are soft-bodied insects which can be green, yellow, black, brown or red.
They are usually small and oval-shaped, and may have dicernable wings or antennae.
Aphids use their piercing, sucking mouth-parts to feed on the sap of plants and usually occur in colonies located on the undersides of stems or leaves.
If a plant becomes heavily-infested, its leaves can turn yellor or wilt due to the excessive sap removal.
Aphids produce large amounts of a substance known as "hondeydew," a sugary liquid waste.
Honeydew drops from these insects and can causes spots on the windows and finish of cars which are parked under infested plants.
A fungus called sooty mold can grow on honeydew deposits which accumulate on the leaves and branches of your plant, turning them black. Many times, an aphid infestation is only noticed after the first appearance of sooty mold.
The drops of sweet honeydew can also attract other insects such as ants.
An infestations is generally the result of a small numbers of winged aphids that fly to the plant and take it up as their new host.
Winged aphids deposit several wingless young on the tender undersides of leaves/steams before moving on to find a new plant.
Immature aphids, or nymphs, that are left behind, feed on plant sap and increase gradually in size.
They mature in 7 to 10 days and then are ready to produce live young. Usually, all of them are females and each is capable of producing 40 to 60 offspring.
The process is repeated several times, resulting in a tremendous population explosions. Less than a dozen aphid "colonizers" can produce hundreds to thousands of aphids on a plant in a few weeks.
Aphid numbers can build until conditions are so crowded, or the plant is so stressed, that winged forms are produced. These winged forms fly off in search of new hosts and the process is repeated.
Solution: Early detection is the key to reducing aphid infestations.
The flight of winged colonizers cannot be predicted, so weekly examination of plants will help to determine the need for control.
Examine the bud area and undersides of the new leaves for clusters or colonies of small aphids. The presence of these colonies indicates that the aphids are established on the plants and their numbers will begin to increase rapidly.
Fatty acid salts or insecticidal soaps are very good against aphids. They apparently work to disrupt insect cell membranes. They require direct contact with the insects and leave no residual effect.
Nervous system insecticides, such as malathion, Dursban (chlorpyrifos), and Orthene (acephate), are labeled for use on many shade trees and ornamental plants for aphid control.
As with soaps, coverage is very important and a follow-up application may be necessary. Sevin (carbaryl) is not effective against many aphids so it is generally not a good choice for control unless recommended specifically.
In fact, applications of Sevin may reduce the number of beneficial insects, such as lady beetles, and increase the potential for aphid outbreaks.
Beneficial insects, such as lady beetles, lady bugs, and lacewings may eat large numbers of aphids but the reproductive capability of aphids is so great that the impact of the natural enemies may not be enough keep these insects at or below acceptable levels.
To keep aphids and other pests off your plants just finely chop1 onion and 2 medium cloves of garlic. Put ingredients into a blender with 2 cups of water and blend on high. Strain out pulp.
Pour liquid into spray bottle. Spray a fine mist on plants, making sure to coat both tops and bottoms of leaves.
Spider Mites
Spider mites are not insects but are more closely related to spiders.
These arachnids have four pairs of legs, no antennae and a single, oval body region.
Most spider mites have the ability to produce a fine silk webbing. Spider mites are very tiny, being less than 1/50 inch (0.4mm) long when adults.
Spider mites have tiny mouthparts modified for piercing individual plant cells and removing the contents. This results in tiny yellow or white speckles.
When many of these feeding spots occur near each other, the foliage takes on a yellow or bronzed cast. Once the foliage of a plant becomes bronzed, it often drops prematurely.
Heavily infested plants may be discolored, stunted or even killed.
Web producing spider mites may coat the foliage with the fine silk which collects dust and looks dirty. Spider mite species seem to be warm weather or cool weather active pests.
The two spotted, European red, honeylocust, and oak spider mites do best in dry, hot summer weather. The spruce and southern red spider mites do best in cool spring and fall weather.
All spider mites go through the same stages of development. Adult females usually lay eggs on their host plants.
The eggs hatch in days to weeks into the first stage, called a larva. Larvae are round bodied and have only three pairs of legs. The larvae feed for a few days, seek a sheltered spot to rest and then molt into the first nymphal stage. The first nymph now has four pairs of legs.
The first nymphs feed a few days, rest and molt into the second nymph. The second nymphs feed, rest and molt into the adult stage.
The males are usually the size of the second nymph and have pointed abdomens. The females have rounded abdomens and are the largest mites present. Most spider mites spend the winter in the egg stage but the twospotted spider mite over winters as adult females resting in protected places.
This cannabis leaf shows the first signs of a spider mite infestation: dozens of tiny yellow spots.
Solution: Early detection of spider mites, before damage is noticed, is VERY important.
The tiny spider mites can be detected only by a full and thorough leaf inspection (on both sides of the leaf). If you find Spider Mites you must act fast and hit them hard.
Shake the plant, then kill the spider mites with something that kills them on contact, like:
- A bleach solution (1 tablespoon of bleach to 1 gallon of 95°F, pH balanced, water in a spray bottle.)
- Alcohol and water mixed togther will also kill the bugs on contact and shouldn't hurt the plant as long as the solution contains at least 30% water.
- SM-90 mixed with water (1 part SM-90 to 5 parts water) kills spider mites on contact and is organic (it even smells good!)
Using bleach, alcohol, or SM-90 seems to work best.
I tend to avoid chemical sprays, or miticides with Abamectin <http://pmep.cce.cornell.edu/profiles...ectin-ext.html> or lindane <http://pmep.cce.cornell.edu/profiles...f-lindane.html> because these are harmful to humans.
There are also insect predators <http://eartheasy.com/grow_nat_pest_cntrl.htm> that can help in providing some CONTROL but this does not mean 100% eradication and in a consumable crop that is what we are after. The predator mite can help to control them if chemical sprays are not your thing.
White Flies / Whitefly
White flies behave just like spider mites.
The insect hides underneath the leaf, sucks dinner from the essential nutrients in the plant.
This results in white spots on the top side of the leaf.
White flies are easily spotted with the naked eye. If you shake the plant a little, they'll fly around. They look like little white moths, around 2 millimeters in size.
Solution: ·A white fly problem can be solved basically the same way as aphids. My favorite way to get rid of them is misting your plants in a solution made of 1 part SM90, 5 parts water.
When you spray the plants, and make sure you get the undersides of the leaves(that's where they lay eggs).
You'll want to do this when the lights are about to go off(or else the leaves will get burned). You can get a sprayer like this one on amazon.com, or at Home Depot for about $12.
Thrips
Thrips are small, fast-moving insects with wings.
They rasp, or grate the marijuana leaves open, and suck the sap out.
Thrips prefer flowering tops, and fresh, young leaves.
Affected leaves have shiny, silvery spots. This is caused by the thrips sucking the chlorophyll out of the leaves.
In spite of the fact that they're small, you can see them marching in columns on an infested plant.
Solution: Thrips can be fought with your favorite insecticide. Or predatory insects, the thrips' natural enemy is Amblyseius cucumeris.
A thrip problem can be solved basically the same way as aphids. My favorite way to get rid of them is misting your plants in a solution made of 1 part SM90, 5 parts water.
You'll want to do this when the lights are about to go off(or else the leaves will get burned). You can get a sprayer like this one on amazon.com, or at Home Depot for about $12.
Lice
Lice are found inside as well as outside. And thrive during the summer months. Lice are the most interested in plants with questionable health.
It's unusual to have a lice problem with a healthy marijuana harvest.
Solution: There are two methods to kill lice, spraying with incecticide SM-90, and setting out assassinator wasps.
The problem with most flying predatory insects is that they're attracted to the high-pressure gas lamps we all love to use, which sends most of them to a quick and fiery death.
Slugs/Snails
The common slug is too common a pest to even need much of an introduction. Slugs attack a wide range of plants, causing anything from slight damage to death.
Unfortunately, these annoying pests attack leaves AND buds, and they can do a surprising amount of damage in a short time, so you want to watch out for them and get rid of them quickly.
They often stay hidden, attacking your plants at night, so stay vigilent for slug and snail damage!
Solution: There is no foolproof method for eradicating slugs.
All one can hope for is to reduce their numbers and protect plants when they're at a vulnerable stage.
Toads, frogs, and beetles eat slugs and are worth encouraging in your garden. One of the best ways of dealing with slugs is to use physical barriers.
Slugs are attracted to saucers, orange rinds, and plastic pots of milk or beer (they drown themselves in ecstasy).
How to Make Beer Trap for Slugs and Snails: mix flour with some stale beer and use it to fill a shallow container. Place in garden with the rim 1 or 2 cm above the ground so that slugs and snails can climb in. Substitute beer for wine, sugar water, juice, or water mixed with yeast.
BE WARNED, the trap will fill up quickly so come back often to empty.
To be sure you're keeping your slimy slug population under control; collect them by hand at night or on damp days. T
ry collecting them under a tile or wet cardboard, and squash all eggs you find while digging. Placing a saucer of salt is another method that will kill snails and slugs.
Martha Stewart recommends coiling a piece of wire around the base of your plants to give slugs a shocking experience.
Grey Mold / Bud Rot / Fungus (Botrytis cinerea)
Botrytis blight or gray mold is a common fungus disease which can cause blights; the most common is Botrytis cinerea.
Botrytis infections often thrive in cool (60 degrees Fahrenheit or 15 degrees Celsius), rainy spring and summer weather.
Gray mold can be particularly damaging when rainy, drizzly weather continues over several days.
Look for masses of silver-gray spores on infected plant parts that are growing in humid areas.
Tiny, black, shiny specks might also be seen embedded in diseased plant tissue.
These are sclerotia of Botrytis: they allow the fungus to survive the winter.
Botrytis blight can affect leaves, stems, crowns, flowers, flower buds, seeds, seedlings, bulbs, and just about any other part of a plant with the exception of the roots.
Solution: The best way to manage this disease is keeping humidity low, maintaining good air circulation, and by regularly inspecting and removing of infected parts of the plant immediately.
NEVER SPRAY YOUR BUDS WITH ANYTHING. Once a bud has been infected, you need to remove the affected parts.
Remove infected flowers, leaves, or the entire plant if it's infected at the base, and take it far far away from your grow area to dispose if it.
Low humidity slows down and prevents mold (50% or less humidity is optimal, especially towards the end of the flowering stage). Also try to maintain lots of air movement with oscillating fans, and lots of air exchange if possible ( via Exhuast air and Supply air).
If you find mold remove it immediately. Once you first find mold, you need to watch your plants like a hawk, as mold spreads quickly.
It is best not to do any mold removal while plants are wet since this could help spread fungal spores during conditions which favor infection.
Also avoid overhead watering, or misting plants, especially if you have had trouble with grey mold in the past.
To promote rapid drying of plants, try to space them to allow good air circulation, and don't hesitate to use fans to help promote good air circulation.
Sanitation and cleanliness alone is not sufficient to control this fungus.
The fungus can produce 60,000 or more spores on a piece of plant tissue the size of your small finger nail.
Even one spore can infect a plant and cause disease.
So, avoid injuring plants in any way.
Do not leave large stubs of stems when taking cuttings.
Ventilate your grow space to prevent high humidity conditions.
Even lowering the humidity slightly can have a significant effect on Botrytis.
Outdoor planting should be planned to provide good air circulation patterns.
This is the most important means of stopping this fungus.
Added protection is available for many crops by applying a fungicide or combination of fungicides.
However, Botrytis can develop resistance to certain chemicals.
An ozone treatment is also an option, ozone is excellent for decimating spore counts in the grow room and a decent UV tube unit placed high in the room with a fan blowing through it can reduce dramatically the risk of botrytis.
Don't spray or burn Sulfer in the flowering stage! You will ruin your crop as Sulfer makes your bud taste really bad, like REALLY TERRIBLE.
However, it is safe to use sulfur in Veg to treat mold, before the buds have started forming. Sulfer seems to get right into the essence of the bud and the taste/smell is impossible to remove. Sulfure will TOTALLY ruin your crop if used in the flowering stage!
Tobacco Mosaic Virus
The tobacco mosaic virus can attack a wide range of plants, including tomato, pepper, eggplant, tobacco, spinach, petunia, marigold, and our beloved herb marijuana.
On marijuana the virus infection causes light and dark green mottled areas on the leaves.
The dark green areas tend to be somewhat thicker than the lighter portions of the leaf. The leaf mottling is seen more easily if the affected plant surface is partially shaded.
Stunting of young plants is common and often is accompanied by a distortion and fern-like appearance of the leaves. Older leaves curl downward and may be slightly distorted.
Certain strains of the virus can cause a mottling, streaking and necrosis of the buds. Infected plants are not killed, but they produce poor quality buds and low yields.
Tobacco mosaic, is incited by a virus. The tobacco mosaic virus is very stable and can persist in contaminated soil, in infected plant debris, on or in the seed coat, and in manufactured tobacco products. The virus is transmitted readily from plant to plant by mechanical means.
This may simply involve picking up the virus while working with infected plant material, then inoculating healthy plants by rubbing or brushing against them with contaminated tools, clothing, or hands. Aphids are not vectors of the virus, although certain chewing insects may transmit the pathogen.
Solution: Virus diseases cannot be controlled once the plant is infected.
Therefore, every effort should be made to prevent introduction of virus diseases into the garden.
Sanitation and cleanliness is the primary means of controlling virus diseases.
Infected plants should be removed immediately to prevent spread of the pathogens.
The use of tobacco products during cultural practices should be avoided to prevent inoculation of plants with the tobacco mosaic virus.
Those people using tobacco or working with infected plant material should wash their hands thoroughly in soapy water before handling your plants.
Pythium Root Rot (Pythium spp.)
Pythium root rot can be caused by several different species of the fungus Pythium.
These fungi are common in field soil, sand or sediment of surface water supplies, and dead roots of previous crops.
Pythium has also been found in some commercially available soilless potting mixes.
Pythium is easily introduced into pasteurized soil or soilless mixes by using dirty tools, dirty pots or flats, walking on or allowing pets to walk on the mixes and by dumping the mixes on benches or potting shed floors that have not been thoroughly cleaned.
When introduced into pasteurized soil or soilless mixes, Pythium can cause severe root rot because it has few competitors to check its activity.
Root rot is also a common problem for those growing directly in water, such as via deep water culture or bubbleponics and this fungus poses a threat to crops grown in just about any hydroponic system.
A great way to prevent root rot in hydroponic systems is to properly aerate the water!
If the reservoir is heavily contaminated with debris or soil harboring Pythium, the fungus can spread to a large number of plants quickly.
If the fungus infests a cutting bed or if contaminated water is used in propagation, large losses usually occur.
Almost all plants are susceptible to Pythium root rot.
Root tips which are very important in taking up nutrients and water are attacked and killed. Pythium also can rot the base of unrooted cuttings.
Symptoms of Pythium include: Stunted plants, root tips are brown and dead, Plants yellow and die, Plants wilt at mid-day and may recover at night, rot may proceed up the stem, brown tissue on the outer portion of the root easily pulls off leaving a bare strand of vascular tissue exposed, and the cells of roots contain many microscopic thick-walled spores.
Solution: Pythium root rot is difficult to control once it has begun.
We HAVE NOT had good luck with Subculture B, Great White and SM-90 to treat root rot, though other growers have reported success killing root rot using those treatments.
Still, even with the amazing power of Aquashield in treating root rot, every effort should be directed toward preventing the disease before it begins.
Pasteurize soil and sand with heat (a microwave) or chemical fumigant treatments.
If the water supply is suspected of being the primary source of Pythium, it may be necessary to treat the water before use.
Slow sand filtration has been shown to be an effective, simple, and inexpensive method for removing Pythium from water.
Cover the treated soil and store it or the soilless mix in an area that will not be contaminated through the introduction of non-treated soil.
Likewise, cover ebb and flow system reservoirs. Disinfest all surfaces, tools, and equipment that will contact the potting mix.
We have also found that Hydrogen Peroxide (H2O2) will work for controlling Pythium in both dirt and hydro for short amounts of time. However, I highly recommend getting Aquashield for a more permanent solution.
Read more about getting rid of root rot attacking your marijuana plants right here
Damping-off (young marijuana seedlings dying)
Damping-off generally refers to sudden plant death in the seedling stage due to the attack of fungi.
These fungi are soil borne and are stimulated to grow and infect the seed or seedling by nutrients released from a germinating seed.
However, seedlings may be injured or killed by something other than fungi, for example, toxic materials in the soil, excess or deficient soil moisture, seed defects, temperature extremes, toxic gases in the air, etc. A correct diagnosis is the key to effective control measures.
Damping-off disease of seedlings is widely distributed and is a problem on a worldwide basis. It occurs in most soils, temperate and tropical climates, and in greenhouses.
The disease affects seeds and seedlings of various crops.
The amount of damage the disease causes to seedlings depends on the fungus, soil moisture, and temperature. Normally, however, cool wet soils favor development of the disease.
Seedlings in seedbeds often are completely destroyed by damping-off, or they die after transplanting.
Frequently, germinating seeds are killed by damping-off fungi before they emerge from the ground, which accounts for poor stands in many crops.
Older plants are seldom killed by damping-off fungi mainly because the development of secondary stem tissue forms a protective barrier and limits fungal penetration.
However, portions of the roots and stems still can be attacked, resulting in poor growth and reduced yields. When seeds are planted in infested soils, damping-off fungi may attack them at any stage.
The damping-off fungi may attack the seed prior to germination, or they may attack after the seed has germinated but before the seedling has emerged above the soil line.
Infected seed becomes soft and mushy turning a brown to black color, and it eventually disintegrates.
Seeds that have germinated and become infected develop water-soaked spots that enlarge and turn brown.
The infected tissue collapses, resulting in death of the seedling.
Penetration and death of seeds before they emerge is termed preemergence damping-off.
Seedlings that have emerged are usually attacked at or below the soil line. The organism can easily penetrate the young soft stem tissue.
The infected stem portion becomes discolored and begins to shrink.
As this occurs, the supportive strength of the stem's invaded portion is lost, and the seedling topples over. The fungi continue to invade the remaining portion of the seedling, resulting in death.
This phase of the disease is termed postemergence damping-off. Older established plants also can be attacked by damping-off fungi.
Usually the new developing rootlets are infected, resulting in root rot. Infected plants show symptoms of wilting and poor growth.
Solution: Proper conditions for seed germination and seedling emergence also favor vigorous growth of fungi that cause damping-off.
Seed and roots must be kept moist and warm until the roots have penetrated the soil and the seedlings have emerged.
As the seedlings continue to grow, moisture at the soil surface can be decreased, and the damping-off fungi then will have less of an advantage.
When watering, thoroughly saturate the soil and then apply no more water until soil approaches the point at which plants wilt.
This procedure will keep surface soil dry for a maximum time.
Pasteurization of Soils is the best way to protect yourself. Soil for growing transplants in flats can be steam pasteurized.
If steam is used, the entire soil mass should be maintained at a temperature of 160 degrees F for 30 minutes.
The home gardener obviously does not have facilities to steam soil; however, pasteurized, packaged soil mix is available from many garden centers.
To prevent soil recontamination, all items such as tools, pots, and flats, etc., must be clean. The items can be cleaned in hot water (160 degrees F for 30 minutes) or in a chlorine bleach solution (1 part bleach to 9 parts water; soak for 30 minutes).
It is important to use fresh chlorine bleach-water solutions.
