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Why Are Cannabis Leaves Turning Yellow?

Are some or all of your cannabis leaves turning yellow? Maybe your leaves also have other symptoms like spots, curling, wilting, brown patches, etc. Marijuana plants may get yellowing leaves for several different reasons, so it can be hard to figure out the true root of the problem!

Today I’ll break down the 10 most common reasons your weed leaves turn yellow, and I’ll show you how to make your plant green again!

10 Most Common Reasons for Yellow Leaves

When Not to Worry (Pictures of Normal Yellow Leaves)

10 Causes of Yellow Leaves (From Most to Least Common)

1.) PH is Too High or Low at the Roots

Whether you’re growing in soil, coco coir or in hydroponics, probably the most common reason to see yellowing and other nutrient deficiencies is the pH near the roots is too high or too low. Cannabis plants have a difficult time absorbing nutrients when the pH is off, resulting in nutrient deficiencies even if the nutrients are actually present near the roots.

Symptoms

  • Yellow or other oddly colored leaves
  • Spots, stripes or patches
  • Burning around the edges of leaves
  • In fact, basically any nutrient deficiency can be triggered by incorrect pH!

How Do Growers Get It?

Growers who don’t make sure their pH stays in the right range will often run into nutrient deficiencies, even if they’re starting with a pure source of water and good soil!

  • Soil Optimum: 6-7 pH
  • Coco / Hydro Optimum: 5.5-6.5 pH

How to Fix

  • Use a kit or PH Pen to test the pH of water before you give it to your plants, and adjust if necessary by adding an acid or base to your water
  • Learn How to Fix Incorrect pH

These symptoms look like nutrient deficiencies but are actually caused by incorrect pH!

Most water sources contain enough copper (which the plant needs in very small amounts) so copper deficiencies like this one are almost always caused by incorrect root pH

Zinc deficiencies are the same way. They are almost always caused by incorrect pH.

Another common culprit of yellow leaves from incorrect pH is a potassium deficiency. Cannabis plants love lots of potassium, especially in the flowering stage, but nearly all cannabis-friendly nutrient systems contain plenty of potassium. If you’re adding nutrients to the water, this deficiency is almost always the symptom of a pH problem.

This is also a potassium deficiency, even though it looks a little like nutrient burn (too high levels of nutrients). The main clue is the yellow striping on the leaves, which tends to get worse over time until leaves are mostly yellow. Another clue is the brown tips go in further than typical nutrient burn.

Stripes on the leaves (click for close-up) indicates that this is not a Nitrogen deficiency, even though the symptoms are similar. In this case, the symptoms were caused by the pH being way too high.

2.) Poor Watering Practices

It’s much more common to over-water than under-water cannabis plants, and the symptoms are very similar. In either case, the solution is to learn how to water your plants exactly the right amount at the right time!

Symptoms of Poor Watering Practices

  • Droopiness (it’s normal for plants to droop a little before the lights go out, but you know the drooping is a problem if it’s already happening at the beginning of their “day”).
  • Odd problems and symptoms from poor water practices including yellowing and sometimes other deficiencies.
  • Overwatering – leaves seem “fat” and swollen with water. Often you’ll have a feeling you may be overwatering your plant, especially if it’s a small plant in a large container.
  • Underwatering – leaves often seem “papery” and thin because they don’t have any water inside them. Chronic underwatering leads to overall yellowing and deficiencies.

How Do Growers Get It?

  • Overwatering is most common with young plants since they still have small, weak root systems
  • You can hurt plants by giving too much or too little water at a time, and you can also cause persistent droopiness by watering too often or too infrequently
  • Bad soil with poor drainage can cause the symptoms of overwatering even if you’re watering the plants perfectly!
  • Small plants in big containers are easily over-watered
  • Big plants in small containers are easily under-watered
  • Growers who spend long periods away from their plants and/or don’t pay attention to their watering needs are much more likely to run into problems with droopiness!

How to Water Your Plants Correctly

  • Start with good soil or coco coir
  • Make sure plants are in the right size container for their size
  • If plants start drooping after you water them, you’re overwatering!
  • If drooping plants perk up after watering, you’re underwatering!
  • Learn how to water your plants perfectly every time!

Overwatering

Chronic overwatering can sometimes cause unusual deficiencies even if the pH is spot on, like this plant grown in muddy soil. The biggest sign that these symptoms are caused by overwatering and not pH (or something else) is that the plant is always droopy.

Another example of a deficiency that’s actually caused by overwatering (notice how this seedling is also droopy)

Chronic Underwatering (Relatively Rare)

Most growers tend to overwater – not underwater – their plants. However, if you’re spending long periods away from your plants or the containers are drying up in less than a day or two, it may mean that your plant needs to be watered more often, or be given more water at a time. It’s also more common to under-water when plants start overgrowing their pots.

It can be difficult to diagnose chronic underwatering because problems may look like nutrient deficiencies. Your main clue is that plants perk up every time after you water.

3.) Nitrogen Deficiency

Symptoms

  • Plants tend to be lime green or pale all over, even though the leaves appear healthy without stripes or spots
  • Yellow leaves tend to appear towards the bottom of the plant
  • Yellow leaves feel soft and are easily pulled off (in fact they usually fall on their own). If a leaf feels very stiff or is hard to pull out, that means it is not a Nitrogen deficiency

How Do Growers Get It?

  • Affects plants which have “used up” the nutrients in the soil, which can happen after the plant has been the same container for several weeks or months.
  • Can happen in coco or hydro when the grower isn’t providing any extra nutrients (since there is no Nitrogen contained naturally in plain coco or water).
  • It is very unlikely you have a true Nitrogen deficiency if you’re providing your plants with the recommended amount of cannabis nutrients in the water.

How to Fix

  • Easily remedied by giving plants a regular base plant nutrient from basically any cannabis-friendly nutrient system
  • In soil, growers can transplant their plants to a new container with fresh soil (if they don’t want to add extra nutrients in the water).
  • Learn more about Nitrogen deficiencies

A cannabis plant turns pale or lime green all over (left) when it needs more Nitrogen. A healthy plant appears medium green (right).

This plant is on the verge of a Nitrogen deficiency. This is indicated by its overall pale color, even though all the leaves look healthy without spots or stripes. Cannabis leaves should not be lime green or pale, or the plant tends to grow more slowly!

Here’s a close-up of a Nitrogen-deficient leaf near the bottom of the plant. Nitrogen-deficient leaves are soft and look/feel wilted.

If you have a Nitrogen deficiency, the yellow leaves will start falling off on their own

Did You Know? Oddly enough, too much Nitrogen can also cause yellow leaves, though the rest of the leaves will be clawed and a deep dark green instead of pale.

4.) Light Burn

Symptoms

  • Yellowing appears most on the parts of the plant closest to the light.
  • Yellow leaves do not pull out easily, even if the whole leaf is dead
  • Light burn often takes a few weeks to develop and is most common once the plant is past the 6th week of the flowering stage (when plants aren’t making many new leaves to replace old ones).

Cannabis light burn usually affects the top leaves closest to the grow light instead of affecting the plant evenly

How Do Growers Get It?

  • Light burn is when your leaves are working too hard for too long, causing them to die early.
  • Even if the temperature is in a good range, your plant can still get light burn if the grow light is too close. It’s kind of like how skiers can get sunburned even in the freezing temperatures because of all the sunlight reflecting off the snow.
  • Light burn is most common with powerful lights like HPS/LED/LEC.
  • It’s also common when switching to new bulbs (which are stronger than old bulbs) or when there is no glass between the bulb and your plants.
  • Some plants are more sensitive than others, and you may have one plant suffering from light burn while the others are fine. That can make it harder to diagnose the problem since some of your plants are thriving in the same environment!

Light burn symptoms can be different from plant to plant, but they always seem to happen mostly to the parts of the plant that are closest to the light

How to Fix

5.) Temperature Problems (Heat Stress / Cold Shock)

  • Yellow or burnt leaves near the light
  • General yellowing of upper leaves
  • Leaves start “turning up” at the edges, or forming “tacos”

How Do Growers Get It?

  • If you put your hand where your plants are and hold it there for 30 seconds, is it too hot to be comfortable? If it’s too hot for you it’s likely too hot for your plants.
  • Although relatively rare indoors since most growers struggle with heat instead of cold, a temperature under 50°F (10°C) can also cause pale or yellow leaves. Some plants will even die if it hits freezing temperatures! Placing grow containers directly on concrete in a basement can kill them with cold overnight!

How to Fix

This poor plant was decimated by a heat wave – it went through several days of 100°F+ temperatures! Luckily the buds were still great 🙂

Too much heat can cause the edges of leaves to curl upwards and make “tacos”.

Sometimes extended periods of high temperatures causes spots and other odd symptoms in addition to yellowing.

Cold Shock

This plant was exposed to temperatures under 40°F (5°C) at night, causing all the newest growth to turn so pale yellow it almost looked white!

6.) Magnesium Deficiency

Symptoms

  • Yellowing in between the veins on leaves, often located lower down on the plant.

How Do Growers Get It?

  • A magnesium deficiency is almost always caused by incorrect pH though if you’re using heavily purified or soft water (such as RO – reverse osmosis – water) you may need a Cal-Mag supplement to make sure your plant is getting enough magnesium.

How to Fix

  • First check the pH. It should be in the 6.0-7.0 range for soil growers and 5.5-6.5 for everyone else.
  • If a Magnesium deficiency persists, consider getting a CaliMagic supplement that is made for plants (you should always add Magnesium and Calcium at the same time because these two nutrients work together in the cannabis plant).
  • Learn more about Magnesium deficiencies

With a magnesium deficiency, the yellowing happens between the veins of the leaves, while the veins stay green.

Sometimes Triggered by Old Age / Natural Senescence / Light Deprivation

  • It’s actually normal if you only see these symptoms on a few leaves at the bottom of the plant that are no longer getting any light. The plant eventually “gives up” on old leaves if they spend days or weeks without light, which often happens to the lowest leaves at the plant gets bigger. This may look like a magnesium deficiency.
  • If this is the case, the leaves often seem droopy, limp and tired. These leaves don’t “stick straight out” like normal leaves because the plant isn’t wasting resources by putting energy into them.
  • This is most common when using relatively weak grow lights like fluorescent lighting or CFLs, since the light doesn’t easily reach the bottom of the plant.
  • Therefore this symptom is only something to worry about if it’s happening on leaves that are still getting light, or if you’re seeing the symptoms on many different leaves instead of just an occasional leaf here and there.

7.) Iron Deficiency

Symptoms

  • Iron deficiencies are unique because the yellowing always affects the newest growth; it does not happen to older leaves that are already green.
  • New leaves usually come in completely yellow.
  • Unlike most other nutrient deficiencies that cause yellowing, yellow leaves from an iron deficiency will usually turn green, starting from the outside edges and working inwards.

How Do Growers Get It?

  • Unless you are using RO or very purified water, an iron deficiency is almost always caused by incorrect pH. This is because cannabis needs very little iron, and most sources of water already contain trace amounts of iron.

How to Fix

  • The pH being too high or too low is the most likely the cause of this problem. Bring your pH into the correct range and iron deficiencies will just go away.
  • If using purified water or water that doesn’t contain much natural iron, you may need a Cal-Mag supplement which includes iron like CaliMagic. You see these three together because Iron, Calcium and Magnesium work closely together in the plant. You never want to supplement your plant with extra iron without also adding the correct ratio of Calcium and Magnesium at the same time, or it may cause other types of deficiencies.
  • Learn more about Iron deficiencies

Iron deficiencies cause the middle and newest leaves to turn yellow, but they will slowly turn green as the plant gets older

8.) Not Enough Light (Seedlings)

When a shell first cracks, the round leaves inside are actually yellow. They only turn green once the plant starts getting enough light.

Note: Adult cannabis plants without enough light won’t grow well either, but they likely won’t have yellow leaves. In fact, adult cannabis plants that are getting relatively low levels of light will actually turn dark green since they aren’t using up nutrients for photosynthesis (the extra unused nutrients get stored in the leaves, causing them to appear darker).

How Do Growers Get It?

You know your seedling needs more light when…

  • Seedlings are tall with small leaves
  • There is a lot of nodal spacing (stem between each set of leaves). Seedlings look “stretchy”.
  • Leaves stay yellow or pale green

How to Fix

  • The solution for pale, tall, stretchy seedlings is to add more light!
  • Learn more about different grow lights as well as how to upgrade your light system

This seedling is yellow and “stretching” because it needs more light

9.) Bugs or Pests

Many different types of bugs or pests can stress your plants, causing them to develop yellow leaves.

Symptoms

  • You can actually see bugs or eggs
  • Yellowing leaves, especially when combined with spots or bite marks
  • Overall lack of vigor

How Do Growers Get Pests?

  • Track them in from outside
  • From visiting another grower’s plants
  • Getting an infected clone or plant (sometimes there’s a few tiny eggs you can’t see!)
  • Certain things like overwatering, lack of cleanliness and poor air circulation make your garden a bigger target and a better home for bugs, making it easier for an infestation to take hold and stick around.

How to Fix

  • Unless you 100% trust the grower and their growing practices, never ever visit another grower’s garden or adopt clones from them. It can be incredibly difficult to get rid of bugs that are already specialized at surviving on cannabis plants!
  • Avoid going straight from outside to your cannabis plants, especially if you’ve spent time in a garden.
  • Make sure there is a screen to stop bugs if your plants are getting fresh air from outside.
  • Identify your bugs and get rid of them!

One of the most common pests that can cause yellowing without really any other symptoms is fungus gnats. These tiny winged creatures hang around your wet topsoil, and are most likely to appear if you’re overwatering your plants. Although the adults don’t attack your plants, their larvae feast on the roots, which can eventually cause yellowing, especially on small or weak plants.

A bad fungus gnat infestation can damage or even kill your plant!

Another common pest that may cause overall leaf yellowing is spider mites!

But any time a plant has an infestation, you may notice the leaves start yellowing regardless of the type of bug. You should be very concerned if you also see spots!

10.) Bud Rot

If yellow leaves appear overnight on just one or a few of your main buds, inspect the areas closely! Sometimes this is caused by bud rot at the base of the leaves.

Symptoms

  • Yellow leaves on select parts of the biggest buds
  • Yellowing often appears overnight
  • Yellow leaves usually easily fall right out
  • At the base of the leaf you can see white, gray or brown mold growing on the inside of the cola

How Do Growers Get It?

  • Humidity above 60% RH
  • Lack of air circulation/breeze
  • Cool temperature – bud rot thrives around 60-70°F
  • Bushy plant (too many leaves) in a small space like a grow tent
  • Outdoors in rainy, cool or humid weather

How to Fix

  • Keep humidity under 50% RH during flowering if possible
  • Keep the temperature above 65-70°F at night if possible
  • Make sure there’s lots of air circulation around all the colas and through the plant
  • Defoliate a very bushy plant, especially if it’s getting close to harvest time
  • Learn how to prevent and treat bud rot!

Sometimes Yellow Leaves Are Normal!

Sometimes marijuana leaves turn yellow for totally normal reasons, including….

First Leaves Turn Yellow – Normal

After your plant has grown a few sets of leaves, it’s very normal for the first few sets of leaves to turn yellow and die, especially if they’re not getting light anymore. You will almost always lose the round cotyledons, the single-finger leaves, and the three-finger leaves (first three sets of leaves).

This vibrant young cannabis plant is healthy and growing over an inch a day

However, if you look closely at the bottom of the plant, you can see the three bottom sets of leaves have turned yellow and are dying. This is normal! The plant does not hold onto these baby leaves for long!

Single-Finger Leaves (plus the tiny round cotyledon leaves)

When just first 3 sets of leaves turning yellow like the example above (leaves with three fingers or less), it’s not something to worry about as long as the rest of the plant is green, healthy and growing fast!

You don’t normally see these in pictures because most growers remove them 🙂

Plant is Ready to Harvest – Normal

Often plants will have a few yellow leaves by harvest time! This is completely normal and nothing to worry about as long as you’ve ruled out bud rot!

Mutation – Cosmetic (Usually Not Harmful)

Occasionally you may see mutations or natural variation that results in parts of leaves being yellow. The general rule of thumb with any unusual leaf symptom is if the rest of the plant is green, vibrant and healthy, there’s usually nothing to worry about.

Are your marijuana leaves turning yellow? View the 10 most common reasons this happens (with pictures) and get the solutions!

Why Marijuana Leaves Turn Yellow And How To Save

Seeing marijuana leaves turn yellow is an alarming sight. As if that is not bad enough, spots, patches, curling, and wilting may soon follow. Since there are so many reasons behind the discoloration, it can be hard to pin down the root cause. But if you know what to look for, then diagnosing the problem is doable, and you can save the plants.

In this article, we list down the most common causes of yellow leaves – as well as how to make the foliage green and healthy again.

What Causes Marijuana Leaves To Turn Yellow

Yellowing leaves is one problem everyone encounters – including experienced growers. Of course, they probably do not have to deal with this problem as much as someone new to growing marijuana. But do not worry – it is solvable, and you will have the plants hale and hearty in no time. It is just a matter of making some simple tweaks in the grow room.

When troubleshooting, the first step is to identify the source of the problem. There are many reasons why the leaves might turn yellow. It can be poor watering practices, improper pH levels, nutrient deficiencies, and pests, among others. The plants may also suffer from more than one.

At any rate, go through the list below to know which category the afflicted plants fall into. Inspect afterward and note any unusual signs aside from discoloration. If you have a grow journal, it is time to whip it out. Administer treatment only when you are a hundred percent sure with your diagnosis.

1. Light Burn And Heat Stress

Cannabis plants, although hardy, can only endure a certain amount of light and heat. Indoors, the grow light needs to be close enough to provide ample illumination, but far enough so that they will not burn the upper canopy.

Light Burnt Marijuana Leaves

If positioned too close, the heat can be excessive, causing the leaves to start yellowing, curling, wilting, and showing other signs of heat stress.

Light burn is more likely to occur with the use of high-intensity discharge (HID) lights. These bulbs – metal halide (MH) and high-pressure sodium (HPS) – provide excellent results but emit a lot of heat. Although more expensive, many are turning to LED and LEC lamps, which does not emanate as much heat but nonetheless could still do so if improperly positioned.

How To Remedy Heat Stress

Light burn typically takes a few weeks to develop. The signs may also differ from plant to plant. Once you see a sign, such as yellowing leaves, the first step is to adjust the lamp, increasing its distance from the canopy. Wait for the plants to recover before gradually moving the bulbs closer. Do not rush it – around a few centimeters at a time will do. Keep at it until you cover the recommended distance between the lights and the bulbs. (Refer to the instruction’s manual of the chosen lamp for more information.)

To avoid heat stress, you need to maintain ideal temperature levels. Remember, cannabis plants prefer a bit of warmth. During the vegetative stage, it should fall around 70 to 85°F (21 to 29°C). Flowering plants, on the other hand, flourish at 65 to 80°F (18 to 29°C). At lights off, slightly lower the temperatures by about 10 degrees.

2. Underwatering

The leaves – both the older and newer growth – can turn yellow when the plants receive too little water. Devoid of water, the leaves soon droop, become brittle and papery, and have burnt-looking leaf tips.

Underwatered Marijuana Plants

Underwatering can be hard to diagnose since the signs are similar to nutrient deficiencies. An indication of dry plants is if they perk up or look rejuvenated after being watered.

How To Prevent Underwatering

It is easy to nurse dehydrated plants back to health. All you have to do is water the plants more often. Be careful not to overwater, ensuring that excess water seeps out of the drainage holes. If growing in soil, water as soon as the top inch feels dry. You can also spray some water on the shriveled leaves to help rejuvenate them.

Growing in too-small containers may also result in underwatering problems. It causes the medium to dry out too quickly, leading to drought conditions at the roots. Hence, make sure to transplant the plants as soon as they outgrow their current pot.

3. Overwatering

Overwatering plants is a common mistake, especially among beginners. It occurs when you give plants too much water, irrigate them too often, or have poor drainage. Of the two watering issues, overwatering is more serious and requires immediate attention.

Overwatered Marijuana Plant

Too much moisture in the medium may result in oxygen deprivation, causing the roots to starve and start dying. As the roots decay, nutrient uptake becomes more limited, leading to deficiencies. The lack of minerals and elements, in turn, causes the leaves to turn yellow, droop, curl inward, and appear firm and swollen, among others.

How To Prevent Overwatering

If you suspect an overwatering problem, the first thing to do is water the plants less often. Again, the top inch of the soil should feel dry to touch before being watered. Remember to drench the plants until the water trickles out of the bottom holes. The growing medium should be damp – not soggy.

If the water pools on top of the substrate or takes too long to leak out of the bottom holes, then it most likely has poor drainage. If so, consider amending it with aerating materials like perlite, compost, and gypsum. Also, ensure that the chosen container has enough bottom holes to facilitate drainage. If not, drill some more. Alternatively, you can also shift to smart or air pots, which are harder to overwater.

4. Improper pH Levels

The term pH stands for “potential of hydrogen” or “power of hydrogen.” It is a logarithmic scale that runs from 1 to 14, indicating the acidity or alkalinity of a solution. Pure water, measuring pH 7.0, is neutral. Anything below is considered acidic, while values above it are basic or alkaline.

Correct pH Level

pH levels play a crucial role in plant nutrition. Marijuana plants, for instance, thrive in a slightly acidic pH range between 5.5 to 6.8. Outside of this range will already interfere with the nutrient uptake, resulting in deficiencies. Eventually, some of the leaves will turn into a sickly yellow shade as the plants starve for essential minerals.

How To Avoid pH Problems

If you suspect pH to be the cause behind the yellowing of leaves, consider testing your soil. You can send a sample to a lab for accurate pH readings. But you can also do it at home using a high-quality digital pH meter. Soil-based cannabis prefers a pH of 6.0 to 6.8. If growing in soilless media, keep it between 5.5 to 6.5.

Adjust the pH level accordingly using pH up or down solutions. To increase the alkalinity of the medium, you can also use potassium hydroxide, liming substances, and wood ash. On the other hand, aluminum sulfate, sulfur-coated urea, and sulfur can bring down the soil pH.

To avoid nutrient-related problems, monitor the pH and adjust as needed.

5. Nutrient Deficiencies

Incorrect pH level at the roots is the leading cause of nutrient deficiencies. For example, a soil pH lower than 6.0 reduces the absorption of phosphorus, calcium, and magnesium. But if it is higher than 7.0, the plants will have a hard time accessing phosphorus, magnesium, copper, iron, and zinc already in the soil.

Marijuana pH Soil Nutrients

Sometimes, the nutrient levels just happen to be low – or they might be absent from the medium altogether. A laboratory analysis is needed to determine the precise nutrient content in your soil. But if you know the symptoms of different nutrient deficiencies, then you can diagnose the problem yourself and figure out exactly which nutrient is lacking.

The most common telltale sign is the yellowing of leaves. It can be triggered by a shortage of nitrogen, potassium, magnesium, and iron, among others.

Nitrogen Deficiency

Nitrogen plays a crucial role in chlorophyll production. It forms the amino acids, which serve as the building blocks of proteins. It is also a part of ATP and is used to build DNA.

Yellowing leaves, especially in older growth, is a major sign of nitrogen deficiency. The affected foliage may wilt and fall off. That is because the newer leaves are stealing most of the available nitrogen from the mature leaves. Eventually, the yellowing may move up and reach the upper leaves.

Potassium Deficiency

Potassium is involved in photosynthesis, the opening and closing of the stomata, the synthesis of proteins and amino acids, and the production of ATP. It also fortifies the plant tissues, increasing their overall resistance.

Potassium deficiency usually manifests as yellowing leaves. Other symptoms include burnt-looking leaf edges or tips, dark spots on fan leaves, curling of leaves, and older growth falling off.

Magnesium Deficiency

Magnesium plays a crucial role in photosynthesis. It is the core of the chlorophyll molecule and assists the plants in creating glucose from light energy. It also helps metabolize carbohydrates, making it more available for the plants. Without enough magnesium, the veins in the leaves will start turning yellow. Eventually, the leafage will curl and fall off.

Iron Deficiency

Iron is not a part of chlorophyll, but it contributes to leaf pigmentation and respiration. It is also involved in energy production. With iron deficiency, the yellowing first affects the newer growth. From the veins at their bases, the discoloration will spread to the older fan leaves. In time, new leaves are often rendered completely in yellow.

How To Fix Nutrient Deficiencies

Before attempting to address the deficiency, make sure that the pH falls within the ideal range first. Afterward, nourish the soil with the missing nutrients.

For a long-term solution, consider treating the soil with organic amendments, such as compost, worm castings, humic acid and fulvic acid, and mycorrhizal fungi. Aside from stabilizing the pH levels, these materials also break down organic matter, making the nutrients more bioavailable to the plants.

6. Pest Infestations

Pest attacks are the bane of every grower’s existence. It may not only damage the garden but compromise the growth and yields of the affected crops as well. Several types of pests and bugs can plague cannabis plants, each with their corresponding symptoms. Fungus gnats are notorious for turning the leaves yellow. You also need to watch out for spider, broad, and russet mites.

Fungus Gnats

Fungus gnats are tiny, fly-like insects that infest and lay eggs on warm, moist soils. It is also heavily attracted to decaying organic matter. Upon hatching, the fungus gnat larvae will start feeding on the roots, eventually damaging it. A common sign of an invasion is when small flies buzz around the plants, especially near the base. You might also spot some translucent larvae writhing on the topsoil.

Marijuana Pests – Fungus Gnats

Aside from yellowing, this pest can also cause the leaves to wilt, droop, and have dark spots or patches.

Overwatered crops provide an ideal environment for fungus gnats to thrive. If you notice an attack, stop watering the plants for a few days. As the topsoil dries out, the fungus gnats will start disappearing as well. To quicken the process, spritz some neem oil on the soil or place yellow sticky cards strategically around the growing area.

Broad Or Russet Mites

Broad or russet mites, like spider mites, often dwell on the leaf undersides, where it lays eggs and sucks on the plant cells. It is practically impossible to see it without a magnifying tool, making it hard to identify. It is also extremely damaging and secretes toxic saliva that can stunt the growth and development of cannabis crops.

Some of the telltale signs of broad and russet infestations include the yellowing, curling, and drooping of leaves. The foliage may also be abnormally glossy. In most cases, the symptoms will appear worse in certain spots, which is where the invasion is centered.

Spider Mites

Spider mites are a common pest, but it can be hard to detect since it is incredibly small. It is usually found on the leaf undersides, laying translucent eggs and creating silk webbings. The mites also have razor-sharp mouths to pierce and munch on the plants, leaving specks and bite marks on the surface. The appearance of yellow or pale spots on the foliage is another clue of an infestation.

Marijuana Pest – Spider Mites

Spider mites like high temperatures and low humidity, reproducing rapidly under these conditions. To lower their population, start by boosting the airflow in the grow room. Have some fans blowing over the canopy and the topsoil. To exterminate the mites and their eggs, spray some contact pesticides on the leaf undersides. Make sure to use only safe ingredients, such as insecticidal soap, garlic, and neem oil.

7. Bud Rot

Bud rot – also known as gray mold or gray rot – is a type of fungus that attacks cannabis from the inside out, eventually causing its decay. It can affect the crops in all stages of growth. The spores also spread quickly across the growing area, contaminating any plants with cuts and tears on the surface. This damaging mold thrives in a cool, moist environment.

Marijuana Bud Rot Leaves

Once infected with bud rot, one or two marijuana leaves may turn yellow overnight. They also usually fall out easily. Mostly, it is due to the white, brown, or dark gray mold feasting on the bud’s interior. The leaves near the entry point of the rot may start wilting as well.

How To Stop Bud Rot

As soon as you detect the bud rot, snip off the decayed parts immediately. Be extra careful so that it will not touch the rest of the plant. Inspect the rest of the growing area, and continue removing any rotted parts. Spray some organic disinfectants on the contaminated plants. Finally, sterilize the grow room to get rid of the fungal spores, focusing on surfaces, gardening tools, and pots.

To prevent the bud rot, you need to adjust the temperature and humidity to suitable levels. Maintain a warm environment of around 77°F (25°C). As for the relative humidity, keep it below 50% at all times. Hygrometers, in this case, will come in handy.

Since the mold proliferates in most areas with poor airflow, make sure that the garden has ample ventilation. Also, prune dense bushes for better air circulation. Pay attention to the middle and lower part of the plant.

When Not To Worry About Yellowing Leaves

Yellow leaves are not always a cause for alarm. It sometimes occurs for perfectly normal reasons as well. For instance, in young cannabis plants, the bottom leaves usually turn yellow and die off as they receive less light. Expect to lose the cotyledons up to the first three sets of true leaves.

Another example is when harvest time looms closer. During this period, growers will flush the plants – or feed them only high-quality water instead of nutrients up until the collection. Doing so forces the plants to use up any leftover nutrients, resulting in smoother, more flavorful buds. Eventually, the leaves should lose their color.

Yellow marijuana leaves is a problem that many growers face. In this article, we discuss why it happens as well as ways to prevent or remedy it.