This article on beet curly top virus in cannabis plants is largely based on the invaluable contributions of Whitney Cranshaw. Cranshaw has built an extensive repository on hemp pests (note: hemp and high-THC cannabis are the same species of plant, and experience the same pests) and generously offers pest pictures and information to the cannabis-growing and scientific communities.

I would also like to thank Dr. Punya Nachappa, Judith Chiginsky, and Bob Hammon for contributing online resources on beet curly top virus in cannabis plants to help create a comprehensive information sheet [PDF] on the subject. For further reading, Colorado State University offers more excellent cannabis pest information sheets.

Pictures of Cannabis Plants with Beet Curly Top Virus

Some cannabis plants get yellow and stunted, but may not show the “curly top” symptoms. First, the “curly top” everyone’s talking about:

“Leaf curling associated with infection of hemp by beet curly top virus.” ~Whitney Cranshaw

“‘Classic’ symptoms of beet curly top virus infection of hemp, with generalized yellowing of the plant, without leaf distortion, and stunting.” ~ Whitney Cranshaw

Leafhoppers Spread Beet Curly Top Virus!

Check out the full page on leafhoppers (one of the leading vectors for beet curly top virus in cannabis plants).

The beet leafhopper is a host for Beet Curly Top Virus, and easily spreads the disease while feeding. Photographer: A.C. Magyarosy

It is possible other types of leafhoppers, or other insects, could be spreading the virus among marijuana plants, though more information is needed.

What is Beet Curly Top Virus and How Does it Infect Cannabis Plants?

Beet Curly Top Virus (BCTV) is a cannabis plant disease that is transmitted by the beet leafhopper (Neoaliturus tenellus) and possibly other forms of transmission (other bugs, transferring the virus from one plant to another during handling, etc).

Beet Curly Top Virus (BCTV) can infect a wide variety of host plants, including sugar beets, tomatoes, beans, spinach, and cannabis (hemp) plants. I heard about beet curly top virus at the Cannabis Business Conference in 2022, though it initially was identified in cannabis plants in 2020 or earlier.

“Beet curly top virus infection showing both yellowing and strong leaf curling.” ~Whitney Cranshaw

“Closer view of a hemp shoot exhibiting leaf curling and twisting due to Beet curly top virus” Credit: pnwhandbooks.org

How the Virus Spreads to Cannabis Plants

Most commonly, the disease is spread through leafhoppers (a common cannabis pest), which feed on infected plants and then spread the virus to a clean plant on its next feeding.

So far, the Worland (BCTV-Wor) and Colorado (BCTV-CO) strains of the beet curly top virus have been identified in Colorado, but there are likely other strains affecting cannabis plants in different parts of the world.

Symptoms of Beet Curly Top Virus in Cannabis Plants

BCTV can cause a wide variety of symptoms, though the curling of new growth (“curly tops”) is the most striking.

• Twisting of new growth (“curly tops”) – New growth on the plant may display a strong twisting or curling pattern. This new growth may remain green or turn yellow. Leaves tend to curl upwards
• Stunted size – Slow growth is common, and plants may stay small or act like “runts” even if they don’t show other symptoms.
• Leaf yellowing or mottling – Early stages of infection may produce light yellowing or mottling, mostly at the base of a leaf. Over time, this yellowing may become more pronounced and eventually whole plays may become pale yellow and stunted
• Localized symptoms – Some plants may only have symptoms on certain spots, while the rest of the growth appears normal. For instance, the original stem might develop curly top symptoms, while side branches that develop later have typical growth patterns.

The total effects (overall health, yield, and other potential issues) of beet curly top virus on cannabis plants are still not fully understood, because the virus’ ability to affect cannabis plants was discovered relatively recently.

Some hemp or cannabis plants infected with the virus can outgrow most of these symptoms, but it’s still a good idea to get rid of them anyway to prevent future transmission. We need to do more research to discover all the strains affecting cannabis, and how they differ from each other.

“‘Bisymptomatic’ hemp plant infected with beet curly top. In this condition, the original plant stem shows strong symptoms of infection, including yellowing and leaf distortion. On the same plant, side shoots develop that appear symptom free.” ~Whitney Cranshaw.

How to Treat Beet Curly Top Virus (Prevention)

Unfortunately, because there is no cure for beet curly top virus, the best thing for a cannabis grower to do is get rid of all cannabis plants known to be infected by BCTV.

Note: It is possible to use plant tissue culture to grow a clone of the infected plant (typically done in a lab by experts), which gives you a clean uninfected plant with the same genetics. However, there is no way to cure a plant that already has the virus. Even if it outgrows its symptoms (which occasionally happens), it will still be able to infect other plants. Therefore it’s highly recommended to carefully dispose of infected plants.

1. Carefully get rid of infected plants – If you suspect your plant has beet curly top virus, separate it immediately from your other plants, and consider throwing it away to prevent the potential spread of the virus to other plants.
2. Get rid of leafhoppers (if any) – If you suspect your cannabis got infected due to leafhoppers, then a preventative step is to control the local leafhopper population.
3. Clean entire grow area – Outdoors, clean the area around the plants (rake up any leaves, treat for bugs, etc.). Indoors, it’s a good idea to sterilize any part of the grow space that may have touched infected plant matter.
4. Take care when touching plants – Until you’re during the virus is gone, take extra care whenever you’re touching one plant and then another. For example, if you’re defoliating or cutting off parts of the plant, make sure to change gloves before you start on another plant. You don’t want the juices from the inside of one plant to touch the inside of another plant.
5. Start with seeds – Clones will typically carry the virus if the parent plant was infected, but cannabis plants grown from seeds are rarely infected (even if their parents were). Dip seeds briefly in a 10% hydrogen peroxide solution before germination to ensure the virus is not on the seed coat. This doesn’t prevent the plant from catching the virus later, but starting with seeds helps give you a small amount of protection because, without any infected plants around, transmission is impossible.

Protect your cannabis plants from viruses so they can focus on producing amazing buds.

Conclusion

In this tutorial, we’ve unearthed vital insights about the Beet Curly Top Virus (BCTV) and its bearing on cannabis plants. From its varied host plants to its symptoms and strains, BCTV is a formidable threat that requires keen observation and swift action.

Key takeaways for cannabis growers

• Understand the Virus – BCTV is a disease transmitted to cannabis plants by beet leafhoppers and possibly other means. Simply being aware of this and its many host plants prepares you to intervene swiftly when the first signs of infection appear.
• Spot the Symptoms – Identifying the symptoms of BCTV is crucial for early detection. Curling of new growth, stunted growth, leaf mottling or yellowing, and localized symptoms are key indicators of potential infection.
• Transmission – The primary transmission method is through leafhoppers or other mechanical damage (like pruning first an infected plant and then a healthy one without washing your hands between). Understanding how transmission works can guide you toward effective control measures, like carefully handling plants and managing leafhopper populations.
• Management and Control –  Although there is no cure for BCTV, there are practical strategies for managing an outbreak. Disposing of infected plants, eradicating leafhoppers, thoroughly cleaning the grow area, and minimizing plant-to-plant contact can help curb the spread of the virus. If you’re concerned your current stock of genetics may have the virus, start your next grow with known clean plants (or seeds) to help ensure you have clean stock.

Remember, the best defense against BCTV is a strong offense. Stay vigilant, act quickly, and employ these strategies to safeguard healthy cannabis plants and yield. The journey to understanding and managing BCTV is ongoing, and your proactive efforts are a critical part of that process.

If you have pictures, information, or experience with beef curly top virus in cannabis plants, please don’t hesitate to contact us so we can help share the word!

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Overall growth of the marijuana plant may be stunted. With a manganese deficiency, the yellowing will begin at the base of the leaves and move outwards towards the tips.

Solution for Manganese Deficiency in Cannabis

Your plant may also exhibit signs of a manganese deficiency if the pH is too high, or if the plant is getting too much iron.

Learn how to manage your pH when growing cannabis.

Please note: After a manganese deficiency is cleared up, the problem (brown spots and yellowing leaves) will stop spreading to other growth usually within a week. Please note that leaves which have been damaged by a manganese deficiency will probably not recover or turn green, so you want to pay attention to other growth for signs of recovery.

• In soil, manganese is best absorbed by the roots in the 6.0 – 7.0 pH range (some growers recommend keeping the pH slightly lower, from 6.0 – 6.5, if you suspect a manganese deficiency in particular)
• In hydro, manganese is best absorbed by the roots in the 5.5 – 6.0 pH range (in hydro, it’s generally recommended to keep the pH between 5.5 – 6.5, but manganese specifically tends to be best absorbed below 6.0)

If you suspect your growing cannabis plant has a manganese deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes manganese. This will remove any extra iron or nutrient salts that may be affected the uptake of manganese, it will help restore pH to the proper levels, and will supply the plant with any missing nutrients.

You are looking to avoid higher pH ranges, as this is where manganese deficiencies are most likely to occur.

If you cannot get rid of your manganese deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems

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Cannabis Copper Deficiency Symptoms

• Leaves turn dark with blue or purple undertones
• Tips and edges of leaves turn bright yellow or white
• Shiny or metallic sheen on leaves
• Leaves may feel stiff and start turning under
• Tends to affect leaves directly under the light
• Buds do not ripen, or grow very slowly

The pale tips of a cannabis copper deficiency look a little different from nutrient burn, which may start out with slighly yellow tips, but soon makes tips appear brown or burnt.

This is what the yellow leaf tips of a cannabis copper deficiency looks like. The most telling feature of a copper deficiency is that the rest of the leaf darkens and takes on a blue or purple cast which makes the yellow tips look bright in comparison. The leaves also often appear shiny and may feel stiff.

Some strains are prone to copper deficiencies in the flowering stage, which can create dark purple or reddish hues in the leaves directly under the lights. The following picture shows a Blue Widow plant where all the leaves under the light turned purple due to too-bright light and incorrect pH triggering a copper deficiency.

A cannabis copper deficiency tends to affect the leaves directly under the light. If your grow light is close it may help to move lights a little further away.

A big problem with a major copper deficiency if it happens early in the flowering stage, is the affected leaves are not good at photosynthesis and won’t provide nearly as much energy for the buds as they would if they were green. It’s important to keep leaves near the buds healthy during the majority of the flowering stage to help ensure you get the best yields possible. While it’s normal for leaves to start dying in the last week or two before harvest, you should react quickly if you’re seeing unhealthy leaves earlier than that!

It is very unlikely that there is no copper available in your water or soil, so usually a copper deficiency in cannabis is caused by a pH problem at the roots that is restricting access to nutrients.

Copper toxicity (too much copper) in cannabis plants is rare, though a severe case of too much copper can cause a quick death to the plant.

Solution For Cannabis Copper Deficiency

1.) Adjust pH to Correct Range

The most common reason growers will see copper marijuana deficiencies is when the pH at the roots is not in the correct range. Copper tends to get locked at certain pH levels, and is better absorbed by the plant in a slightly acidic root environment.

If you suspect your growing cannabis plant has a copper deficiency due to incorrect pH, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients. This will remove any nutrient salts that may be affected the uptake of copper and help restore pH to the proper levels..

Watch to make sure that the problem starts to clear up within a couple of days. Old growth may not recover, but new growth should be healthy.

• In soil, copper is best absorbed by the roots in the 6.0 – 7.0 pH range
• In hydro, copper is best absorbed by the roots in the 5.5 – 6.5 pH range

Learn how to manage your pH for growing cannabis.

2.) Give the Right Nutrients

The truth is, most cannabis growers don’t need to add more copper in response to a copper deficiency!

In fact, most growers have actually already given plenty of copper to their cannabis plants since it is found abundantly in most tap water. If you’re using quality soil or cannabis-friendly nutrients, you probably don’t need to worry about adding more copper. In general, copper deficiencies are more likely to appear when a grower is using heavily filtered or reverse osmisis (RO) water to feed plants since any copper has been removed, but pH is a much more common reason growers see copper deficiencies in their cannabis plants.

3.) Take Good Care of the Roots

Copper deficiencies can show up with the plant is having root problems or if the plant is overwatered, even if the pH is right and the copper is there. Proper watering practices help plants grow healthy and avoid a host of problems!

4.) Watch for Leaf Recovery

After going through all the above steps, watch to make sure that the copper deficiency starts to clear up within a few days to a week or so. The damaged leaves may not completely recover all their green, but you know you’re in the clear when you stop seeing symptoms appearing on new leaves.

If you cannot get rid of a cannabis copper deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems with chart!

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Solution For Cannabis Zinc Deficiency

Note: Sometimes a cannabis zinc deficiency (like all deficiencies) can be triggered by stressful conditions and may clear up on its own after the period of stress is over. However, to minimize damage it’s important to react to any growing problem as quickly as possible, especially in the flowering stage.

1.) Adjust pH to Correct Range

The most common reason growers will see a zinc deficiency is when the pH at the roots is too high. Zinc tends to get locked at higher pH levels and is better absorbed by the plant in a more acidic root environment.

If you suspect your growing cannabis plant has a zinc deficiency due to too-high pH, flush your system with clean, pH’d water. This will remove any nutrient salts that may be affecting the uptake of zinc and help restore pH to the proper levels.

• In soil, zinc is best absorbed by the roots in the 6.0 – 6.5 pH range (although it’s generally recommended for soil growers to keep pH in the 6.0-7.0 range, zinc tends to be absorbed better on the lower side)
• In hydro, zinc is best absorbed by the roots in the 5.5 – 6.0 pH range (although it’s generally recommended for hydro growers to keep pH in the 5.5-6.5 range, zinc tends to be absorbed better on the lower side)

Learn how to manage your pH for growing cannabis.

2.) Give the Right Nutrients

The truth is, most cannabis growers don’t need to add more zinc in response to a zinc deficiency!

In fact, most growers have actually already given plenty of zinc to their cannabis plants since it is found abundantly in most tap water. If you’re using quality soil or cannabis-friendly nutrients, you probably don’t need to worry about adding more zinc. In general, zinc deficiencies are more likely to appear when a grower is using heavily filtered or reverse osmosis (RO) water to feed plants since any zinc has been removed, but pH is a much more common reason growers see zinc deficiencies in their cannabis plants.

3.) Take Good Care of the Roots

Zinc deficiencies can show up with the plant is having root problems or if the plant is overwatered, even if the pH is right and the zinc is there. Proper watering practices help plants grow healthy and avoid a host of problems!

4.) Watch for Recovery

After going through all the above steps, watch to make sure that the zinc deficiency starts to clear up within a few days to a week or so. The damaged leaves may not recover completely, but you know you’re in the clear when you stop seeing symptoms on new leaves.

If you cannot get rid of a cannabis zinc deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems

The post Zinc Deficiency appeared first on Grow Weed Easy.

The parts underneath the leaves may take on a pinkish red or orange color. The buds on a flowering plant may start dying off. Unlike most other deficiencies that cause yellowing of the leaves, a sulfur deficiency will start at the back of the leaf and move it’s way forward as opposed to starting at the tips.

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.

The post Sulfur Deficiency appeared first on Grow Weed Easy.

Problem: A light green or yellow coloring will begin to show on the veins and edges of the lower & older leaves – this is one of the classic signs of cannabis magnesium deficiency. You may also see red stems.

Magnesium is a mobile nutrient, which means that the plant can move it from old leaves to new leaves.

If you don’t react to it promptly, a cannabis magnesium deficiency can spiral out of control and cause your plant to lose a lot of lower leaves quickly. The plant will pull magnesium out of older leaves and bring them to the newer leaves. That’s why a magnesium deficiency usually appears towards the bottom of the plant and on older, less important leaves.

The edges of the leaves may become yellow or bright green and may start feeling crispy to the touch. This crispiness around the edges is different from nutrient burn, which does not lighten the margins inside the leaves.

You may see red stems with a magnesium deficiency, though not always.

Sometimes you will also get light brown spotting within the margins or along the edges if the problem continues to get worse, though this may be partially other deficiencies, which often happen alongside a magnesium deficiency.

Magnesium deficiencies are easy to prevent and fix once you know what to do. Read on below to learn how.

Solution For Magnesium Deficiency in Cannabis

A magnesium deficiency sometimes happens after supplementing plants with something that contains calcium but not magnesium, such as agricultural lime (non-dolomite lime), egg shells, etc. This won’t happen with proper cannabis nutrients. If you’re using good nutrients, cannabis plant may still show signs of a magnesium deficiency if the pH at the roots is too low, especially in hydro. That is because when the pH of your root zone is not in the correct range, your cannabis cannot properly absorb magnesium through the roots.

Often with this deficiency, the magnesium is present, but the roots cannot absorb the magnesium properly due to an improper pH. Therefore it is very important to maintain the correct pH (and make sure the pH does not get too low / acidic) in order to avoid a magnesium deficiency.

Growers using Coco Coir or Reverse Osmosis (RO) water usually need to supplement their plants with extra Calcium & Magnesium in addition to regular nutrients. Treating coco coir with Cal-Mag and supplying extra throughout your grow is recommended for growers in coco coir, or those using RO water.

Adding more magnesium to a system when there is a pH lock-out will probably not help because the plant will not be able to absorb any magnesium until the pH has been corrected. If there’s already enough magnesium, adding more can cause other apparent deficiencies by locking out other nutrients from the plant.

Please note: Once a magneisum deficiency is cleared up, the problem (yellowing lower leaves) will stop spreading to other older leaves, usually within a few days. Please note that leaves which have been damaged by a magnesium deficiency will probably not recover or turn green, so you want to pay attention to other growth for signs of recovery.

• In soil, magnesium is best absorbed by the roots in the 6.0 – 7.0 pH range (some growers say a 6.5 – 7.0 pH is best if you suspect a magnesium deficiency)
• In hydro, magnesium is best absorbed by the roots in the 6.0 – 6.5 pH range (in hydro, it’s generally recommended to keep the pH between 5.5 – 6.5, but magnesium specifically tends to be best absorbed above 6.0)

If you suspect your growing cannabis plant has a magnesium deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes magnesium. This will remove any nutrient salts that may be affected the uptake of magnesium and help restore pH to the proper levels..

To supplement with extra Magnesium…

Calcium and magnesium deficiencies often appear together in cannabis. Many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case one of these common deficiencies appear.

Listed below are common cannabis Calcium supplements, along 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. Remember, the old leaves will probably not recover, but new growth should be green and healthy.

Cal-Mag is Well Suited For Hydro, Coco Coir, or Soil

General Hydroponics CaliMagic is a calcium and magnesium plant nutrient supplement. General application is to mix 1 tsp (5ml) of CaliMagic into each gallon of water. I have used Calimagic several times with great results.

Organic Dolomite Lime – For Soil Growers

If you’re looking for a way to supplement magnesium in your organic or soil setup, I highly recommend a product called “Dolomite Lime.”

Note: The finer the dolomite, the more quickly it will be available to nutrients

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 buffer pH in soil so it’s easier to maintain the correct neutral pH range which is optimum for cannabis growth, especially in acidic soils.

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.

If watering plants by hand… Flush the system with properly pH’ed water that contains a full set of proper nutrients that are suitable for growing cannabis. Make sure you are using the right nutrients for the stage your plant is in. Check the pH of your runoff water to ensure that nothing in the growing medium is throwing off the root pH.

If growing hydroponically… Check the pH and PPM of your reservoir water to make sure that pH is on target and nutrient levels are not lower than expected. If you do this and are still not certain what is causing the magnesium deficiency, it is recommended that you drain your reservoir and refill with a newly mixed reservoir with fresh nutrients which have been pH’ed.

Should I add extra Magnesium? Some growers will add 1 tsp of Epsom salt/gallon of water and water plants with this mixture in response to a magnesium deficiency (since Epsom salt is primarily made of magnesium).

As I mentioned, often a magnesium deficiency is actually caused by a mix of factors, such as pH being off. Even if the pH is on target, sometimes a magnesium deficiency appears when other important nutrients like iron or calcium are not present in the right quantities.

A great supplement that has all of 3 of these important nutrients is known as Cal-Mag, as this contains Magnesium and Calcium, as well as a trace amount of iron.

Adding extra magnesium is often not necessary if you are using tap water. However, you will likely want to supplement Cal-Mag if you are using filtered or reverse osmosis (RO) water, since most tap water already contains some amount of all 3 of these cannabis nutrients. Cal-Mag also has a small amount or iron, which is another trace cannabis nutrient that is often missing in filtered water.

How long until new growth looks better? If you fix the root of the problem, further yellowing and discoloration of the leaves should stop almost immediately. Some of the affected leaves may recover somewhat, but what’s most important is to make sure the problem isn’t continuing to spread to other leaves on the plant.

I generally don’t remove any discolored leaves until I know for sure that the problem is completely gone and is no longer spreading to new leaves (that way any possible further discoloration will happen to the leaves that have already been affected).

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Problem: Your cannabis plant can only withstand a certain amount of light. After a certain point, your cannabis will start turning yellow or otherwise exhibit signs of stress on the leaves near the sources of light and/or heat.

How far away do I keep grow lights from my plants?

Light burn usually causes yellow leaves at the top of the plant directly under the grow lights (though it can appear on older leaves that have been exposed for a long time).

Sometimes the first sign a plant is getting too much light is all the leaves start pointing up or “praying”, like this (though sometimes you don’t see any symptoms until the yellowing starts)

With light burn, often the inside veins stay green. Yellow leaves won’t fall off or be plucked off easily, unlike a nitrogen deficiency where leaves fall off on their own.

The leaves closest to the light may appear much more pale than the rest of the plant, and tips may turn yellow.

Another example of yellow tips from light burn

Sometimes light burn causes edges of leaves to turn up. If it goes on a long time, the leaves also start to become crispy and can even break off if you try to bend them

You may noticed just the tallest colas getting droopy, which is sometimes a sign the light is too intense (though it could also be caused by root problems or over/under watering)

Light burn is often mistaken for a Nitrogen deficiency which makes wilting yellow leaves. Nitrogen-deficient leaves fall off on their own, while light-burned leaves are hard to pluck off. A nitrogen deficiency starts from the bottom of the plant and moves up, while light burn often is worse at the top of the plant.

Cannabis light burn usually affects the top leaves closest to the grow light

A Nitrogen deficiency creates yellow leaves at the bottom of the plant as the Nitrogen is sucked out of the oldest leaves to feed the top of the plant. On the other hand, light burn produces yellow leaves at the top of the plant under the grow lights because the leaves have worked too hard and/or too long from the light being too close. The leaves aren’t able to keep up with regular plant processes.

Imagine sitting outside all day under a scorching sun, possibly for days on end. Even if you could handle it for a day or two, it might wear you down over days or weeks.

How can there be too much light if there’s no heat? Read the full guide

It’s probably light burn if mostly just the leaves closest to the lights are turning yellow

With cannabis plants that have light burn, your leaves can sometimes become yellow or red/purple, possibly with brown spotting, often with burnt tips/edges and margins that stay green. Other problems, like nutrient problems, can trigger or make the symptoms of light burn a lot worse. Leaves may also appear generally burnt in places when there’s too much light, especially when combined with heat or nutrient problems.

Nutrient deficiencies make light burn worse!

If you see light bleaching and unhealthy discoloration only on the parts of the plant directly under your grow light, or only on older leaves that are exposed to the light, it often means it’s too bright for your plants and you should move your grow lights further away! If your plant is also having other problems, it is much more likely to be affected by light burn. A healthy plant can withstand higher light levels than a sick plant.

If the lights are only slightly too close, maybe just an inch or a few cm, the yellowing from light burn may happen slowly over the course of days (or even weeks!) because leaves are dying early instead of immediately. Because of that, light burn may first appear on somewhat older leaves, which can be confusing and make it hard to diagnose.

This cannabis seedling is being burned by too-close LED grow lights

Another example of light burn from an LED grow light being kept too close to the plants

These leaves of this LED-burnt plant started curling upwards

This cannabis seedling basically grew up into the grow light! The heat from the bulb caused massive burning everywhere it touched. If a plant’s leaves directly touches the lights, it leaves “burns” from the heat of the bulbs.

This plant was green and healthy through the vegetative stage under an LED grow light, but the leaves started dying soon after flowering started (even though that distance had been fine in the vegetative stage). The reason was the LED was too close. This is also very common with LED grow lights with just read and blue diodes, without any diodes in the green spectrum.

These plants seem apparently healthy, but the top leaves keep getting lighter and lighter, in this case from a 600W HPS that was kept just under a foot (30cm) away. The leaves slowly turned yellow over the course of a few weeks, getting light burn even though the temperature was a comfortable 75°F (24°C).

These yellow leaves were caused by an LED grow light that was too close. If you don’t realize it’s light burn, the symptoms are inexplicable!

A mild case of marijuana light burn is often mistaken for a nutrient deficiency or a pH problem, but if you look closely, the symptoms are concentrated directly under the grow light.

Light Bleached Cannabis Buds Sometimes Turn White

This is how you get “albino” or white buds. Light bleaching is most common with high-power LEDs and HPS grow lights because these can be brighter than the sun. Basically, bud bleaching is what happens when buds get too much light, kinda like how hair can get bleached if you spend plenty of time in the sun. Except a “sun-burnt” bud is often less potent, and may have lost it’s “cannabis” smell!

Buds which have been bleached tend to be low potency or even have no potency (no available THC or other cannabinoids). Therefore you should avoid light-bleaching your plants at all costs!

Sometimes light-bleached cannabis will get mis-labeled as “albino cannabis” or “white cannabis” but the truth is that the white color is not healthy, so this is not a desirable trait (even if it looks pretty cool).

Most of the Time, Light-Burned Buds Appear Burnt

Often though, light burned buds look like they’ve been burned.

LED-burnt cannabis buds – notice how all the tiny “sugar leaves” have turned yellow or brown

In this case the LED-burn caused the leaves closest to the LED to turn red. Although the buds smoked pretty well anyway, they definitely weren’t as pretty as they could have been!

The leaves too close to the LED grow light turned yellow and wilted. For some reason, cannabis plants seem a lot more prone to light burn after they start flowering.

Another example of a bud that has light burn from a too-close LED

Light burned bud on top, healthy bud below

Solution: If your marijuana plants are getting too much light, try removing some of the lights or moving your grow lights further away from the tops of the plants. If you can’t move the light further away, bend your plants over so the tops are further away or if your plant is still in the vegetative stage you might even consider cutting off the top of the plant to remove some of that height.

Reduce power of grow lights and/or move them further away from your plant
(How far away do I keep grow lights from my plants?)

It is unlikely for your plants to get “light-burned” from the sun when growing outdoors, and they definitely can’t accidentally grow into the sun. Outdoor plants can show signs of light stress if plants were used to shady conditions and moved into direct sunlight without time to get accustomed to the brigher light levels. It also may be possible in extreme high light conditions if the plant is unprotected but in general cannabis plants like a lot of light.

When making changes to your plant’s environment, it’s best to make changes relatively slowly if possible. For example when moving a cannabis plant from indoors or outdoors you might consider giving the plant some shade for a few days before moving it into full sunlight.

Sometimes heat stress can look like light stress. When learning how to grow cannabis, it’s best to try to keep things at a comfortable temperature at all times for optimal growth. If it’s too hot for you, it’s probably too hot for your plants. Outdoors, it’s a lot harder to control temperature, but there are steps you can take to protect your outdoor plants from the heat including supplementing with sea kelp, partially covering them and making sure they’re well watered.

5 Ways to Deal with Heat When Growing Cannabis Indoors

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