5-Step Solution to 99% of Cannabis Growing Problems

by Nebula Haze


Table of Contents

Step 1: Verify Watering Habits & Root Health

Step 2: Diagnose Nutrient Problems & Deficiencies

Step 3: Check Environment for Common Problems

Step 4: Identify Issues with the Grow Light

Step 5: Is it Actually a Pest? (sometimes you never see the bugs)

Still Not Sure? View Picture Guide to Plant Problems



Click here to view the following Cannabis Problem-Solving Flowchart, or continue reading the 5-step cannabis solution article below

Click here for a cannabis problem-solving flowchart


When it comes to growing cannabis, it’s inevitable that you will eventually run into growing problems. I’ve never met a single grower who’s never had ANY problems.

So don’t beat yourself up when growing problems happen. They happen to every grower!

Overwatering is often difficult to diagnose because it can cause a surprising number of symptoms

Our interactive Plant Doctor tool shows you how to identify common cannabis growing problems on sight, but since many problems look similar, you may need a more in-depth diagnosis to pinpoint the root of the issue. This article will walk you through the process of diagnosing almost any growing problem.

Just remember; how you react to problems determines whether you harvest tons of potent buds… or end up totally killing your plants. The way you react to problems is a strong reflection of your ability as a grower. Anyone who stays calm and is willing to search for a solution (instead of giving up) is on their way to becoming a true master grower.

Growing cannabis can be easy when you have the right information, and this article will tell you exactly how to react to problems as they arise.

Nutrient burn is a common grow issue, but some symptoms look similar yet are caused by something else. This tutorial will help you determine the true source of the problem.

Nutrient burn, which causes burnt and sometimes curling tips, is something to be avoided in the marijuana flowering stage!

Luckily, bringing your plant back to peak health is actually pretty simple… which explains why I can do it!

Arm yourself with the knowledge of these 5 simple things to check when your plants get sick, and you’ll know how to give your plants a 100% recovery.

These tips were specially made to fix a whole host of possible issues with minimal work.

Catching and solving problems quickly means bigger, bulkier, more potent buds. Your cannabis plants will love you for it!



Step 1: Verify Watering Habits & Root Health

In a metaphorical sense, the roots are the heart of your cannabis plants. When roots become sick, the health of the entire plant quickly falls apart.

For marijuana plants, your roots are like the "heart" of the plant

Drooping or wilting is the main symptom of watering or root problems. Plants droop when they have “wet feet” for too long, if they get too dry between waterings, or if their roots get sick.

This seedling is droopy because it's been given water too often

Yet sometimes, cannabis plants with unhappy roots show no signs that there are problems until things become grim. Luckily, it’s easy to check for issues and even easier to solve them once you know what to do.

Watering and root problems can also cause a variety of other symptoms including yellowing, nutrient deficiencies, leaf spots, brown edges, curling, and more.

What to do: Use the checklists below to diagnose whether your plant is over-watered, under-watered, or has a root problem.

Check for signs of overwatering

Overwatering is easily the most common grow problem, but it can be tricky to diagnose. Go through this list carefully and if you suspect overwatering, check the link below to see pictures and get detailed solutions.

  • Plants seem droopy (at least some of the time), especially the day after getting watered
  • Plants seem to be getting nutrient deficiencies even though you’re on top of nutrients and pH
  • Brown spots on the serrated edges of leaves
  • Burn or brown markings appear on leaves after watering
  • Unexplained yellowing or bleaching
  • Slow growth or stunting
  • Curled or stunted leaves
  • Green algae growing on your topsoil
  • Plant feels very heavy for its size (a sign that there’s a lot of water in the grow medium)
  • Grow medium seems overly saturated and never dries out on top
  • If water is not draining freely, or if it takes plants a long time to dry between waterings, you may actually have a problem with drainage.
  • Little seedling in a big pot (it takes care to avoid overwatering in this situation)
  • Fungus gnats (little black flies) are buzzing around your soil. These only appear when the topsoil stays too wet for too long.
  • Plants are allowed to sit in runoff water after being watered
  • Smell the root area of your plants. Go on, no one’s looking! If you can, smell the bottom of the pot where the excess water comes out. The water that runs out the bottom should generally have a neutral smell. A ‘stinky’ smell is an indicator that your plant may be suffering from ‘root rot’ or other problems due to high levels of moisture for too long.

Learn how to spot and treat overwatering (with tons of pictures and a comprehensive watering guide)

Check for signs of under-watering

  • Plants seem droopy (at least some of the time) or wilted
  • Plants seem better right after getting watered
  • Nutrient deficiencies appear even though you’re on top of nutrients and pH
  • Dark green coloring
  • Slow growth
  • Grow medium looks dry or dusty
  • Grow medium is very airy and drains quickly
  • Plant feels very light for its size (this means there’s not much water in the grow medium)

Learn how to spot and treat under-watering (not as common, but it happens!)

Under watered marijuana plant is thirsty!

Root Rot

  • Roots can get mushy and “rot” in a grow medium that stays really wet for a long time, though typically root rot happens in a hydroponic setup
  • The main symptom is brown or smelly roots
  • Plants display symptoms very similar to over and under-watering (deficiencies, discolored leaves, drooping, etc.)
  • Learn how to prevent and treat root rot

In hydroponics, root health is key to success. React quickly if you noticed roots look brown or unhealthy

Example of the clawing, curling leaves caused by cannabis root rot (root problems) During a heat wave, the cannabis roots began to show signs of root rot

Tips for healthy roots

  • Start with a great grow medium including super soil, good potting soil, coco, or hydro. Don’t use dirt you find outside or low-quality potting mixes like Miracle-Gro soil.
  • Water potted plants properly! Make sure water can drain freely from potted plants, and don’t water too often. Learn how to water potted cannabis plants so you never run into problems.
  • Make sure that roots get plenty of oxygen. With potted plants, the growing medium should be relatively loose as opposed to dense. Roots need oxygen to stay healthy. If you have a thick grow medium, mixing in some perlite is an easy way to adds more pockets of air. In a hydroponic setup where the roots are growing directly in water, the more bubbles the better (up to a point), as this dissolves lots of oxygen directly in the water. Water that is a lower temperature can also hold more oxygen than water at a higher temperature. That means controlling the temperature is extra important in a hydroponics setup.
  • If you’re using a non-standard growing medium (anything besides soil, coco coir, hydro, etc.), know how to take care of your plants in their growing medium. For example, it can be difficult to grow cannabis in something like straight perlite unless you maintain a water reservoir because perlite can not hold any water. Straight rockwool is bad for the opposite reason, it holds onto a lot of water and not enough air.
  • Your plant roots cannot be allowed to dry out or sit in stagnant water. Roots need a good mix of both moisture and oxygen for the fastest growth
  • Add a root supplement to your water to encourage healthy roots.

Hydroguard is my favorite root supplement, it’s cheap and will build up colonies of good bacteria that out-compete the bad bacteria and actually promote plant growth. Awesome for hydroponic tubs, but helpful in any situation where you’re trying to innoculate roots and keep them healthy.

Get Hydroguard on Amazon.com

Another common root supplement is kelp extract, usually provided as a small amount of liquid fertilizer that contains seaweed. Seedlings love it. Kelp supplements can help protect against heat stress and root problems with potted plants, but are usually not suitable for hydroponic setups as the organic material can clog up tubing.


Step 2: Diagnose Nutrient Problems & Deficiencies

Cannabis nutrient problems are often closely related to the pH at the roots of your plants. That’s because when the root pH is off, it can cause your plant to show signs of a nutrient deficiency, even if the nutrients are actually there in the soil.

Even if you’re providing nutrients, plants may get nutrient deficiencies if the pH is off. This magnesium deficiency is the result of the pH being too low at the roots.

This marijuana leaf is showing signs of a magnesium deficiency (yellow stripes in between the veins)

Growers need to monitor their root pH in almost all growing setups for the best results. Cannabis plants prefer a slightly acidic root environment. Some growers get lucky and the pH of their water happens to be just right without additional adjustment or monitoring. Yet most growers will achieve better growth and plant health by monitoring pH. Being aware of your pH helps you understand when things are going wrong. Luckily, nutrient and root pH problems are easy to solve with the right information.

Cannabis plants cannot absorb nutrients properly if the pH at their roots is too high or too low. So even if the nutrients are present, you’ll still get what look like nutrient deficiencies if you don’t maintain the right pH. This copper deficiency is the result of bad pH even though the plant was getting nutrients in the water.

Cannabis plant has copper nutrient deficiencies on all its leaves

For those of us who aren’t lucky enough to magically have the right pH, here’s how to ensure your plants get exactly what they need.

What to Do: The goal is to give your plant exactly the kind of nutrients it needs to thrive, and provide the correct pH at the roots so your plants can properly absorb nutrients.

First, if you are providing your plants with nutrients, check your nutrients to make sure they have all the necessary elements and minerals for proper growth. If you’re not sure what they need….

Soil: An easy and simple nutrient system for beginning cannabis growers in soil is Fox Farm Liquid Nutrient Soil Trio.

Get Fox Farm Soil Nutrient Trio - a great all-in-one nutrient system for growing cannabis

Coco or Hydro: A time-tested, simple nutrient system for growing cannabis hydroponically (including in soilless mediums like coco coir) is the General Hydroponics Flora Trio.

General Hydroponics Trio is a great nutrient system for growing marijuana hydropnoically

If you want to cut through the technical marketing talk and get straight to what works, it’s important you learn a little bit about what kind of nutrients are needed by the cannabis plant during different stages of growth. These days, there are lots of nutrient systems available that are specifically formulated for plants like cannabis, and they help take all the guesswork out and give your plants exactly the nutrients they need. It doesn’t have to be expensive to provide everything you cannabis plant needs! Learn everything you need to know about cannabis-friendly nutrients.

Second, even if you are providing your plants with the correct amount of nutrients, you still need to monitor and adjust the pH to prevent nutrient deficiencies. How to check & adjust pH for growing cannabis.

Adjusting your pH only takes a few minutes, and your cannabis garden will thank you!

Once you’re positive you’re watering correctly, providing the nutrients your cannabis needs, and you’ve adjusted the water pH to the proper levels, nutrients problems should start clearing up quickly. Remember, if leaves get damaged from a nutrient problem, it is unlikely that particular leaf will ever recover and turn green. What you’re looking for is that the problem stops spreading, and that any new growth appears green and healthy.


Step 3: Check Environment

If you’ve ruled out problems with watering, nutrients, and pH, there’s a strong chance something with the environment is causing your symptoms.

A good growing environment is crucial to the health of your plants. When the temperature (and to a lesser extent the humidity) is too high or too low, your plants will not grow properly no matter what else you do. Plants seem unhealthy and buds just don’t fatten up. You may also end up with problems related to plant stress such as hermies.

Too much heat (or arid conditions) will generally sap the strength of your plant and force it to drink more water than normal for plant transpiration (the process of water movement through a plant and water evaporation through leaves, stems, and flowers). A plant drinking more water than usual can have unexpected consequences. Sometimes hot, dry temps can cause unexpected nutrient burn (plant tips curl or turn brown from high levels of nutrients) because your plant is absorbing more nutrients than normal at the roots, alongside the extra water.

If there is a particular source of heat that is harming the plant (like a hot grow light), you’ll know because the leaves closest to the source of the problem will wilt and turn a brownish color. Learn more about how cannabis plants respond to heat stress.

A generally too-hot environment can cause the stems of your plant to droop as if under or over-watered, even when there’s plenty of water at the roots.

Plants that suffer from extreme heat stress for too long may not recover and sometimes are unable to straighten their posture and continue growing.

Heat stress dramatically slows down growth and buds don’t fatten as much as they could

Cannabis plants with crispy brown leaves after suffering from heat stress

One of the reasons you need great air circulation is your plants “breathe” CO2 during the light hours, almost like we breathe oxygen. Unless your plants are in a big open space with lots of air, or you are supplying your plants with CO2, you need to have some sort of exhaust system to pull away hot, stale air and bring in new fresh air for your plants.

If you’re worried about the smell of cannabis, make sure any heated air being vented outside grow room/house gets filtered to remove the scent of cannabis. For example, many growers choose to get a carbon scrubber to “scrub” all odors before the hot air is vented. By creating good suction with an efficient exhaust system and adding a carbon scrubber, you can basically eliminate all smells from the grow room, inside and outside of the house. Learn more about controlling odors from the grow room.

An exhaust system doesn’t have to be anything fancy. At its simplest, an exhaust system can be two holes and a fan (with the fan place in one of the holes pointed out from your grow area). Having a fan constantly pulling hot air out and bringing fresh air in from your intake hole will help ensure that your plants have the fresh air they need.

With any exhaust system, your goal is to vent out hot air, and replace it with fresh, cool air

Because your plants need CO2 when the lights are on in order to function properly, a completely sealed off grow box is not good unless you’re artificially adding CO2. Your plants will suffer if they don’t get enough CO2 in a sealed grow box even if the temps are completely under control.

Some growers like to supplement their plant with extra CO2 in an attempt to increase yields or growth rate, but it’s important to note that the amount of CO2 found in regular air is plenty for your plants unless you have extremely powerful grow lights (1000W HPS, high power LEDs, etc).

For most growers, a proper exhaust system and a few strategically placed fans are all you need when it comes to air circulation.

Learn how to make an exhaust system for your plants (it doesn’t have to be hard or cost an arm and a leg!)

Learn more about controlling temperature in the grow room

Watch Your Humidity, too! Very high or low humidity can cause slow growth, though high humidity may be worse because it can also trigger white powdery mold and bud rot.

Humidity is a term used to describe the amount of water vapor present in the air at any given place, and the amount of water in the air is related to the local temperature. Learn more about how temperature and humidity are related.

Humidity measures the amount of water in the air. A humidity between 40-60% RH works great in most situations

40-70% Relative Humidity is ideal for vegetative cannabis plants - This pictures shows a humidity monitor (called a hygrometer) in the correct range

It is common for new growers to not pay attention to humidity at all, and this can sometimes cause otherwise unexpected and/or inexplicable problems.

Cannabis plants can show false signs of nutrient deficiencies when the relative humidity of the grow area drops below 35% RH, especially when things get really dry. Younger plants are most susceptible, though plants often adjust over time many plants are able to grow just fine as long as they’re provided with plenty of water at the roots. Some strains can handle low humidity better than others.

Extremely low humidity can cause plants to grow slower and less healthy

Plant drying out, curling, drooping, wilting overnight - drinking less

Young plants, new clones, and vegetating plants that are used to more humid conditions are usually the hardest hit by a dry spell.

Cannabis humidity chart

In the flowering stage, humidity should be kept below 55% to prevent the chance of mold and increase resin production.

Younger plants usually are fine with high humidity, but humidity is especially dangerous in the flowering stage because the insides of the buds can grow mold and still look fine from the outside at first.

High humidity in the flowering stage causes bud rot, which quickly spreads from plant to plant and can ruin an entire harvest overnight. The leaves on this bud became discolored overnight.

When you look closer, you can see the entire inside has started molding and rotting 🙁 This entire bud had to be tossed, and the rest of the plant was harvested immediately before it kept spreading.

In addition to preventing bud rot, there’s some evidence that maintaining low humidity environment in the flowering stage helps buds produce more terpenes (giving buds a stronger natural scent) and more trichomes (possibly even increasing the potency of your buds!).

What to Do: Get a temperature and humidity monitor. Control heat by whatever means necessary and keep humidity in check using the steps outlined below.

Monitor the temperature and humidity with a thermometer/hygrometer in your grow space

Regardless of your setup, it’s important for air to be moving around your plants to prevent heat spots, strengthen stems, help stop pests, reduce the chance of mold, and make sure your plants are getting plenty of fresh CO2 to achieve the best growth.

When it comes to fans, don’t point fans directly at plants or they may get wind burn. Usually, it’s better to be point fans at a wall to disperse the air, or have fans blowing over and under the plant canopy. A fan circulates air in the room and provides a gentle breeze for your plants. A small fan costs less than $20!

Growing cannabis circulation diagram

Best case scenario is you want to set up your fan system so that all the leaves on the plant are gently rustling, yet no stems or branches are waving around from the force of the wind.

When the humidity is too low, it’s important to make sure you provide plenty of fresh water to your plants at all times. You may need to reduce the total amount of nutrients as the plants will drink more water and therefore absorb more nutrients through their roots than when the humidity is not as dry.

When it comes to controlling humidity indoors, you may need to use a humidifier and/or a dehumidifier to keep the humidity in the optimal range. A humidifier adds moisture to the air while a dehumidifier takes moisture out.

Controlling your grow room humidity is one of the tricks that separates the expert growers from the beginners.

You can get some pretty fancy humidity gauges to place in your grow room, and products to help change the humidity are commonly found at department stores, hardware stores, or most stores that sell home appliances. There are also some DIY options discussed in our complete article about controlling indoor humidity.

Here’s the most important things to keep in mind when it comes to the humidity of your cannabis grow room.

  • Vegetative stage: it’s good to aim for a humidity of 40-60% during the vegetative stage
  • Flowering stage: humidity should be below 55% (around 45-50% is ideal) during the flowering stage to prevent bud rot, help buds grow more dense, increase resin production, and cause your plant to produce more terpenes (the stuff that makes your buds smell great). However, lowering the humidity below 40% RH (especially with a plant that’s used to higher humidity) can increase the chance of your plant running into problems or deficiencies.

With the right tools, the task of maintaining humidity can be close to automated, and you will see huge benefits compared to the amount of time and money you invest.

When the air feels moist or humid (or a humidity monitor alerts you to high humidity), it’s extra important to ensure that plants get plenty of air circulation and have lots of air movement. You also want to avoid letting leaves touch each other during periods of high humidity. You can fix constantly too-humid conditions with an exhaust system, fans, and possibly a dehumidifier.

If plants are very leafy and leaves are laying on top of each other, it dramatically increases the humidity of the grow space. In this case, removing leaves (defoliation) can help. Try to remove leaves that are in the lower/middle part of the plant, leaves that are covering bud sites, and leaves that are touching each other making wet spots.

White Powdery mold most often attacks big leafy plants in small spaces

When the air is too dry indoors, you can either choose to let your plants grow hardened to the arid air, or you can use something like a “swamp cooler” (evaporative cooler) to add humidity while also reducing the temperature of your room. A humidifier will also add humidity, but tends to raise the humidity of the room.

Learn everything you need to know about controlling humidity in the grow room

Step 4: Identify Light Issues

Cannabis loves light! But not too much…

When growing cannabis, the mantra when it comes to lights is usually “More is better!” To be honest…it’s true! More light usually is better!

Generally speaking, more light is better for growing marijuana

You see, light is like “food” for your marijuana plants. When plants are growing very slowly, but aren’t showing signs of other problems, the cause is often that they aren’t getting enough light.

The amount of light you give your plants is strongly correlated with fast your plants grow, as well as how much buds your plants will produce during the flowering stage.

Learn 15 tactics to increase cannabis yields

Many new growers don’t realize they’re not giving their plants enough light. As a very general rule, you want at least 100W worth of electricity going into your indoor grow light to harvest a few ounces. More is often better.

More light = More yields + Faster Growth (up to a point)

If plants are growing very slowly, if they’re not drinking much water, or otherwise aren’t doing well without showing any other major signs of problems, often the problem is the plant simply needs more light to thrive.

As a very general and unscientific rule, a new grower who doesn’t run into major problems can expect…

  • CFLs, T5s, and other fluorescent grow lights – Average harvest of 0.25-0.5g/watt
  • HPS and LEDs – Average harvest of 0.5-1g/watt
  • An average growers should expect a harvest on the lower side, an experienced grower can expect a harvest on the higher end (or more!)

This rule is referring to how many watts of electricity are actually being pulled out of the wall, not some sort of “equivalent” amount of watts. If an LED pulls 90W of electricity from the wall, you should plug that into the equation, not the claim that it’s “equivalent” to a 400W HPS light. Same for CFLs, if you have a CFL bulb that pulls 26W of electricity from the wall, you should count that as 26W, and ignore the fact that it says “equivalent to 100W” on the front.

Of course, this rule varies quite a bit depending on the type of light, the strain being grown, the size of the plants, etc. However, it’s a good general guide if you’re not sure how much light you need, and it can help you decide if you might not have enough light for your plants.

To put that into perspective…

  • A good 300W LED grow light will net the average grower about 150g or yield, or 5 ounces of dried bud
  • A 300W LED grow light will net the experienced grower about 300g, or 10 ounces of dried bud

Recommended LED grow light in that range: HLG 300L R-Spec (I love this light!)

Keep in mind that there are many other factors that go into this, and this is not a guarantee as much as a general rule. Moreover, many smaller lights tend to get better yields per watt than fewer larger lights. Lights that are kept closer to plants (without signs of light stress) will also tend to produce bigger yields and faster growth. Most importantly, the strain you start with and the training methods you use to get your plants to more efficiently use your indoor grow lights will have a huge impact on your growth rates and final yields.

But can there be too much light?

Yes, there can be too much light!

Unfortunately, more light is not always better. Cannabis plants can be fickle. You want to give them very bright light… but not too much light.

When marijuana plants are young, they are weak and cannot tolerate much light at all. Yet as they get older, and especially in the flowering stage, marijuana plants want almost all the light they can get.

Marijuana plants light bright light... but not TOO bright

The problem of too much light often occurs indoors, when your grow lights are too close to the plants. This essentially gives them their own version of sunburn.

Young plants, seedlings and new clones are especially prone to suffering from too much light, though it can affect older plants too. The main way you know your plants are suffering from light burn is if only the leaves closest to the lights are affected, and you’ve already covered all the other possible issues in this article.

The intensity of a grow light that is too close will dry up a plant, cause bleaching/yellowing, turn the edges of its leaves brown and crispy, almost like nutrient burn, and other odd symptoms. Learn more about light-stressed plants.

Too high light levels will cause light burn

The top leaves of this cannabis plant are drooping, have turned yellow with brown tips and edges, and is overall not healthy as a result of the light being too close (LED light burn)

High Pressure Sodium (HPS) lights have the meanest reputation for ‘light-stressing’ plants, but many of the newer, more powerful LEDs (Light Emitting Diodes) do it, too!

Learn more about all the available cannabis grow lights

What to Do: Most importantly, pay attention to your plant and watch out for signs of light stress, which will only affect the parts of the plant closest to your grow lights.

For HPS, Metal Halide and CFL grow lights, use the ‘back of your hand’ test.

Back of Your Hand Test – For MH, HPS, CFLs and T5 grow lights (not always effective for LEDs or very high-power HPS lights with strong air conditioning)

  1. Set up your grow lights and turn them on (make sure they’ve had time to warm up)
  2. Gently place your hand – palm down – right above the tallest part of your plant
  3. Wait 10-15 seconds
  4. If the heat coming from the light feels too warm for your hand, then it’s going to be too much light for your cannabis.

LEDs generate very little heat, but can still light-stress plants, so it’s best to keep LEDs the distance recommended by the manufacturer. Each grow light is different, so it’s hard to make generalizations, but just about every LED needs to be at least 10″ inches away from your plants. In my experience, most hobby-sized LEDs (100-300watt true power draw) need to be kept 18-24″ away in my experience. Some LEDs need to be kept even further away, up to 3 feet or more for some of the newer, extremely powerful LED models.

LED grow lights usually need to be kept at least 18-24″ away to prevent light burn

Use caution when attempting to move your grow lights closer, and avoid moving them more than an inch closer in a day, so you can watch the plant’s reaction.

Make sure your grow space is light-proof! (Unless growing an autoflowering strain)

If you’re growing photoperiod plants, you also need to ensure your grow space is totally light-proof, so light can’t get into the tent when the grow lights are off. Photoperiod plants need complete darkness during their dark period or they’ll never make flowers. If photoperiod plants start getting light at night while budding, it can cause them to herm (buds get seedy) or re-veg (buds die and plant reverts back to the vegetative stage).

If you’re growing a photoperiod plant, light leaks can cause seedy buds

Seedy buds with calyxes popping open everywhere

Or re-vegging (the main symptoms are rounded leaves on long stems and dying buds)

This cannabis was put outside too early in the year, causing it to re-vegetate with strainge twisted growth


Step 5: Diagnose Pests (sometimes you never actually see the bugs)

When growing in soil, bugs are a common pest to marijuana gardens. At GrowWeedEasy.com, we believe that growing marijuana in coco is often simpler for beginners because it automatically eliminates many of the bug problems growers run into when growing in soil, while achieving faster growth.

Sometimes you don’t see bugs. Thrips are an example of a pest that leaves markings on the leaves which can be mistaken for deficiencies, yet you rarely see the bugs themselves.

A cannabis leaf with thrips damage

Broad mites are also commonly mistaken for other issues because the bugs are usually too small to see. Broad mites cause twisted growth and shiny, discolored leaves.

This marijuana plant has been infested with broad mites or russet mites, as a result the new growth is twisted and unhealthy

Hemp russet mites “poop” out extra stuff at the top of the plant that can be mistaken for mold

Closeup of hemp russet mite infestation on cannabis plants appear like a yellow or tan mass

However, usually you can tell when plants have bugs because you see the bugs themselves, or it actually looks like bites on the leaves.


What to Do: If you notice any signs of bugs or mold, don’t wait. Act quickly!

One of the worst types of pests for cannabis growers are spider mites. They actually have earned the nickname “the borg” because of their ability to seemingly come back from the dead and take over an entire grow room or destroy a whole crop.

Spider mites are another common pest. You can often see them moving under the leaves, or you’ll notice the webbing and bite marks.

They're hard to see, but there are definitely spider mites on this leaf!

Fungus gnats are another common cannabis pest. They look like tiny flies buzzing around the soil and are the result of overwatering.

A cannabis fungus gnat is about the thickness of a quarter

Leafhoppers look pretty, but they munch on your plants so don’t ignore them!

Example of a pink, red, blue, purple and yellow leafhopper - this color of leafhopper is pretty common in the USA

When you believe you have bugs…

As mentioned earlier, good air circulation and a slight breeze is not only good for the plant by itself, but will also disturb bugs and make it harder for them to turn your plant into a home.


Bonus: Still Not Sure? Picture Guide to Plant Problems

Going through the previous steps will solve quite a few different problems you could be running into, but what if none of the ones mentioned so far seems to apply to your problem?

If you’ve gone through all the above steps, and you’re still having an unexplained growing problem, the following list of common plant problems may help you discover exactly what you need to do next. Click the symptoms to filter through results:

An accidental revegging of cannabis causes unusual new growth and smooth leaf edges

Accidental Re-Vegging

"Re-veg" is short for "re-vegetation" and refers to what happens if a flowering plant stops flowering and re-enters the vegetative ...
Read More
Cannabis plants with aphids have pale or dark bugs under the leaves, typically with white specks (baby aphids and their exoskeletons)


Aphids are soft-bodied insects which can appear white, green, yellow, black, brown and red, depending on their stage of life and ...
Read More
Barnacle scale insects look like unmoving growths on your cannabis stems and leaves

Barnacle Scales

These unusual bugs hang out on your stems and under your leaves without moving. Scale insects suck the life out ...
Read More
A cannabis boron deficiency causes brown patches on leaves and causes thick, twisted or abnormal new growth.

Boron Deficiency

A boron deficiency in cannabis is relatively rare unless a plant is underwatered or in a really dry environment, and ...
Read More
When broad mites attack cannabis they cause droop or twisted new growth, especially near the top of the plant, along with blistered and glossy looking leaves

Broad Mites

Broad mites on your cannabis plants are so tiny they are practically impossible to spot with the naked eye, and can ...
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Bud Rot on cannabis causes dying leaves to appear on the buds, and upon investigation you'll be able to see mold at the base of the leaves

Bud Rot or Mold

Bud rot in cannabis plants is caused by mold, and is most likely to appear when buds are dense and the ...
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A calcium deficiency in cannabis causes brown spots on the leaves

Calcium Deficiency

Calcium is an important nutrient which helps provide structure to the cannabis plant and helps it withstand stress like from ...
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Caterpillars and inch worms can leave holes in your cannabis leaves

Caterpillars & Inchworms

Sometimes the first sign of caterpillars / worms / cabbage loopers is just seeing chunks of your leaves missing. You may also see ...
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Example of a copper deficiency on a cannabis plant. The leaves turn dark, almost shiny looking, and edges and tips of leaves turn yellow

Copper Deficiency

A cannabis copper deficiency appears with leaf symptoms such as dark leaves that take on blue or even purple undertones. The ...
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Crickets don't infest cannabis often, but they can chew small holes in your leaves, and mole crickets can tunnel under your plants


Crickets will happily eat your cannabis plants and leave small holes in your leaves. Mole crickets may be found digging around ...
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Fungus gnats looks like tiny flies buzzing around the soil, and are typically triggered by wet soil conditions

Fungus Gnats

A fungus gnat is so small it's thinner than the width of a quarter. They commonly appear when cannabis plants ...
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Example of grasshopper damage on a cannabis leaf


Grasshoppers (and sometimes locusts, which are basically just grasshoppers with wings) will happily eat your cannabis leaves, leaving holes, and live ...
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Heat stress causes cannabis leaves to start cupping (turn into "canoes"). Another symptoms is leaves pointing up

Heat Stress

Your cannabis plant can only withstand a certain amount of heat and light. After a certain point, your cannabis will ...
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Hemp russet mites on cannabis symptoms (yellow mass of bugs, tops of plants droop)

Hemp Russet Mites

Hemp russet mites are tiny bugs that attack cannabis plants. In fact, they are so small you can only see ...
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Male plants, hermies and bananas are not good. The first sign is "bananas" or "balls" where buds should be

Hermies, Pollen Sacs & Bananas

Did you know there are “male” and “female” cannabis plants? Yes, cannabis plants are “dioecious” plants, which means each plant shows ...
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A cannabis iron deficiency causes the top and inner leaves to turn yellow or white

Iron Deficiency

A cannabis iron deficiency is usually seen first on bright yellow new leaves, and the symptoms of a cannabis iron deficiency ...
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Cannabis leaf damage from a leaf miner looks like a pale trail on the leaf

Leaf Miners

The term "leaf miner" is a common name for a type of pest actually lives inside the tissue of the leaf. These ...
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Leaf septoria on cannabis plants causes round yellow or brown spots on leaves

Leaf Septoria / Yellow Leaf Spot

Sometimes called "yellow leaf spot" or "leaf septoria," this condition is caused by a fungus (or sometimes a bacteria) that attacks ...
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Leafhopper damage on a cannabis leaf (appears as brown spots in clusters)


These pests will happily munch on your leaves, leaving brown or yellow spots. They can sometimes spread certain plant diseases ...
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Light burn or light stress on cannabis plants causes the leaves or tips of leaves to turn yellow. The worst symptoms are usually closest to the grow light.

Light Burn or Light Stress

Your cannabis plant can only withstand a certain amount of light. After a certain point, your cannabis will start turning ...
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The lower and older leaves start turning yellow between the veins when a cannabis plant gets a magnesium deficiency

Magnesium Deficiency

A light green or yellow coloring will begin to show on the veins and edges of the lower & older ...
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Manganese deficiency symptoms on a cannabis plant

Manganese Deficiency

Leaves may become yellow in between the veins, with mottled brown spots on the affected leaves. These brown dead patches ...
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These mealybugs look like white hairy bugs on your cannabis, leaving white patches that look like mold or webbing


These white and hairy bugs enjoy warm temperatures and don't tolerate the cold. They have even been known to grow and spread ...
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A cannabis molybdenum deficiency causes red or pink coloring on the leaves

Molybdenum Deficiency

he initial symptoms may appear similar to a nitrogen deficiency (yellowing of older, lower leaves). Leaves may become mottled or ...
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Example of a nitrogen deficiency (the lower cannabis leaves turn yellow and fall off)

Nitrogen Deficiency

A cannabis nitrogen deficiency will cause the older, lower leaves on your plant to turn yellow, wilt away and eventually ...
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Example of a cannabis plant with a nitrogen toxicity (dark green leaves with the tips turned down)

Nitrogen Toxicity

Dark green leaves, shiny leaves, clawing, weak stems, and overall slow growth. Marijuana leaves that are nitrogen toxic often get ...
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Burnt leaf tips as the results of cannabis nutrient burn

Nutrient Burn

Nutrient burn or fertilizer burn is one of the most common beginner cannabis growing problems. The yellow or brown leaf ...
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Signs of an over-watered cannabis plant includes droopiness and wilting


After watering, your plants start drooping. Usually the droopy leaves will feel firm and appear curled down (the whole leaf ...
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PH fluctuations can cause brown spots on middle or lower leaves

pH Fluctuations

Managing pH is crucial for cannabis plants to be able to take up nutrients through their roots. When the pH ...
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Example of a phosphorus deficiency on a cannabis plant (leaves get dark splotches and eventually drop)

Phosphorus Deficiency

A cannabis phosphorus deficiency generally appears on leaves from the lower/older parts of the plant. The lower leaves may turn ...
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Planthoppers are common cannabis pests - main symptom is white fuzzy patches, bugs take many forms


by Nebula Haze Planthoppers can attack and infest cannabis, leaving a unique cotton-like growth while they suck the life out ...
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A potassium deficiency in cannabis causes burnt leaf tips and edges, as well as yellowing between the margins

Potassium Deficiency

With a marijuana potassium deficiency, you'll generally see symptoms on older leaves, but not always. Sometimes you'll see the symptoms at the ...
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Root problems in cannabis can cause a variety of symptoms, which can look like almost anything

Root Problems

Cannabis plants with root problems show many symptoms. They may appear overwatered or droopy, leaves curl or cup, wilted, slow ...
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Root Rot

Root Rot

Slimy, brown, twisted or unhealthy roots are caused by unwanted pathogens in your hydroponic tank! Curled, drooping, unhealthy leaves are ...
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Slugs and snail damage on cannabis leaves looks like a bunch of bites were taken out of the leaf (which is what happened) often accompanied by a trail of slime

Slugs or Snails

Although not the most common cannabis pest, slugs and snails are unwelcome visitors when they do show up! Sure signs ...
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Spider mites on cannabis cause spots on the leaves. You'll also start to see webbing and tiny bugs if you look closely

Spider Mites

Spider mites are part of the mite family and are related to spiders, ticks, and other mites. Although they’re a ...
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Young stink bugs massing on eggs that were laid on cannabis leaves

Stink Bug

Various species of stink bug have been known to attack cannabis plants. They lay distinctive patches of white eggs, which ...
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A sulphur deficiency in cannabis plants causes leaves to turn yellow (starting from the back of the leaf)

Sulfur Deficiency

A sulfur deficiency is relatively rare and will manifest itself as all-over chlorosis (yellowing of leaves), usually starting with the ...
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Thrip damage on cannabis leaves


Thrips are small, fast-moving insects and can come in many forms, from pale wormy looking things to dark or golden ...
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Tobacco mosaic virus gives cannabis plants odd yellow markings and twisted growth

Tobacco Mosaic Virus (TMV)

Tobacco Mosaic Virus (TMV) is a virus that is commonly found in tobacco plants which causes splotchy or twisted leaves, strange mottling ...
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Under watered cannabis plants wilt or droop, and the leaves become limp and lifeless


If your plant is drooping, then it’s usually a sign of either over or under-watering. Leaves often seem “papery” and ...
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WPM causes white powdery patches on leaves or stems that may resemble flour

White Powdery Mildew

White powdery mildew is usually a minor annoyance that's easily fixed, but if you don't catch it early, white powdery ...
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White flies look like tiny white moths when they're flying around and otherwise behave a bit like spider mites; hanging ...
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Wind burn causes curled or clawing leaves in the direct flow from a fan

Wind Burn

Most indoor cannabis growers use fans to blow air around within the grow area. This creates a nice breezy environment that ...
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Zinc deficiency on cannabis plants cause the top leaves to turn yellow

Zinc Deficiency

With a cannabis zinc deficiency, younger leaves start yellowing in between the veins. Leaf tips get discolored and start dying ...
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