Why Are My Cannabis Leaves Curling?

Learn the most common reasons why cannabis leaves curl and what you can do to fix the problem!

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Cannabis leaves usually curl when they are getting too much light. The edges of the leaves start to turn up, and the leaves themselves get thinner and narrower. This is called “leaf cupping.” Curling leaves can also be a sign of temperature stress, nutrient deficiency, or transplant shock.

If your cannabis leaves are curling, it is important to figure out the cause so that you can fix the problem. Otherwise, your plant will not be able to grow properly and will produce less bud.

The Science Behind Cannabis Leaf Curling

Have you ever wondered why your cannabis leaves are curling? It’s a common problem that growers face, but the good news is that it can be fixed. The answer has to do with the plant’s physiology and how it responds to certain environmental stressors. Let’s take a closer look at the science behind cannabis leaf curling.

The Process of Photosynthesis

Photosynthesis is the process that allows plants to convert sunlight into food. Chloroplasts in the plant’s cells collect sunlight and use it to convert water and carbon dioxide into oxygen and glucose. The glucose is used by the plant as energy and is a building block for other molecules the plant needs, such as cell walls and chlorophyll.

Oxygen is released as a waste product of photosynthesis. Most of the oxygen in our atmosphere comes from photosynthesis by land plants, algae, and cyanobacteria.

Photosynthesis occurs in two stages: light reactions and dark reactions. Light reactions use light energy to produce ATP (adenosine triphosphate) and NADPH (reduced nicotinamide adenine dinucleotide phosphate). These molecules are then used in the dark reactions to convert CO2 into glucose.

The Three Main Types of Cannabis Leaf Curl

There are three primary types of cannabis leaf curl, each caused by different pests or conditions:

1. Leaf Roll: Leaf roll is typically caused by either a virus or a mite infestation. If you see white or yellow stippling on the leaves, it’s likely caused by mites. If the stippling is brown or rust-colored, it’s likely caused by a virus. Both viruses and mites can be controlled with spraying, but it’s important to identify the correct pest before treating.

2. Fusarium Root Rot: Fusarium root rot is caused by a soil-borne fungus that attacks the roots of the plant. The leaves will start to curl and turn yellow or brown, starting at the bottom of the plant and working its way up. Fusarium root rot is difficult to control and can often lead to plant death.

3. Herbicide Damage: Cannabis plants are notoriously sensitive to herbicides, even those that are labeled “safe for use around delicate plants.” If you suspect herbicide damage, stop using any products containing herbicides immediately and flush the soil with plenty of water. Herbicide damage can often be cured, but it may take several weeks for the plant to recover.

Possible Reasons for Cannabis Leaf Curl

There are a few possible reasons why your cannabis leaves might be curling. It could be due to heat stress, lack of nutrients, or even pests. Let’s take a closer look at each of these reasons.

Environmental Causes

There are a number of environmental factors that can cause cannabis leaf curl. These include:

-Too much or too little water
-Excess nutrients
-Temperature extremes
-Humidity levels that are too high or too low
-Pests or diseases

Nutrient Deficiencies

One of the most common reasons for cannabis leaves to curl is a nutrient deficiency. Nutrient deficiencies can occur for a variety of reasons, but are most often caused by incorrect pH levels, or by using nutrient-rich soils that have become depleted. Regular testing of your soil and water will help you to prevent and correct these problems before they cause significant damage to your plants.

Common nutrient deficiencies that can cause cannabis leaves to curl include:

-Nitrogen: Nitrogen is an important element in the development of strong, healthy leaves. A lack of nitrogen can cause the leaves to yellow and curl at the edges.
-Potassium: Potassium is necessary for proper water uptake and helps to prevent drought stress. A potassium deficiency will cause the leaves to dry out and curl.
-Phosphorus: Phosphorus is essential for photosynthesis and helps to promote strong root growth. A phosphorus deficiency can cause the leaves to turn purple and curl at the edges.
-Magnesium: Magnesium is necessary for the proper functioning of enzymes in the plant, and helps to promote vigorous growth. A magnesium deficiency can cause the leaves to yellow and curl.

Pests, Diseases, and Mold

Pests, diseases, and mold can all cause cannabis leaves to curl. Here are some of the most common culprits:

Spider mites: These tiny pests are difficult to see with the naked eye, but they can do serious damage to a cannabis plant. They suck the sap from the leaves, causing them to turn yellow or brown and eventually die.

Mildew: Mildew is a type of fungus that can grow on the leaves of a cannabis plant. It can cause the leaves to curl up and turn yellow or brown.

Bacteria: Bacterial infections are relatively rare in cannabis plants, but they can sometimes cause leaves to curl.

Nutrient deficiencies: If a plant isn’t getting enough nutrients, it may start to show signs of stress, including curling leaves.

Too much water: overwatering your plants can also cause the leaves to curl. The roots will start to rot if they’re constantly soaked in water, and this can cause stress that manifests as curling leaves.

How to Prevent and Treat Cannabis Leaf Curl

Cannabis leaves can start to curl for a number of reasons, including heat stress, lack of water, nutrient deficiencies, and pests or diseases. If you notice your cannabis leaves curling , it’s important to take action to prevent further damage to your plant. In this article, we’ll discuss some of the most common causes of cannabis leaf curl and how to prevent and treat it.

Adjusting the Environment

There are a few key environmental factors that can cause cannabis leaves to curl. If you see your leaves curling, it’s a good idea to check the following:

-Temperature: Both heat and cold can cause cannabis leaves to curl. If it’s too hot, the leaves will curl downward. If it’s too cold, the leaves will curl upward.

-Humidity: Dry air causes cannabis leaves to curl down, while humid air causes them to curl up. Marijuana plantsoriginate in tropical environments, so they prefer humid air. However, too much humidity can also be a problem (see “Bud Rot” below).

-Airflow: Good airflow is important for preventing all sorts of problems, including leaf curl. Stagnant air allows mold and mildew to build up on the plant, and can cause nutrient deficiencies. Make sure your grow room has good ventilation.

To fix environmental problems, you need to adjust the temperature, humidity, or airflow in your grow room.

Addressing Nutrient Deficiencies

Cannabis leaves usually curl when the plant is not getting enough of a particular nutrient. The most common minerals that cannabis plants need are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). All of these minerals are readily available in most commercial plant fertilizers.

If you think your plant might be nutrient deficient, the first step is to test the soil or growing medium to see what minerals are present and in what quantities. Once you know which nutrients are lacking, you can adjust your fertilization program accordingly. It’s always best to err on the side of too little fertilizer, as too much can burn the roots and leaves of your plants.

If you’re growing cannabis in hydroponic system, you’ll need to regularly test the water to make sure the levels of all nutrients are where they should be. Most hydroponic systems have automatic dosing systems that add nutrients to the water as needed, but it’s still a good idea to keep an eye on things and make sure everything is working as it should be.

Treating Pests, Diseases, and Mold

There are several common pests, diseases, and mold that can cause cannabis leaves to curl.

Aphids, spider mites, and whiteflies are common pests that can infest cannabis plants and cause the leaves to curl. These pests suck the sap from the leaves, causing them to turn yellow or brown and eventually die.

To get rid of these pests, you can either use a pesticide or try a more natural method like releasing ladybugs into your grow room.

Several diseases can also cause cannabis leaves to curl. The most common ones are powdery mildew and botrytis (grey mold).

Powdery mildew looks like white powder on the leaves and can eventually kill the plant if left untreated. Botrytis appears as grey spots on the leaves and can also kill the plant if left unchecked.

To treat these diseases, you can use a fungicide or try a more natural method like baking soda spray.

If your grow room is too humid, it can lead to mold growth on your cannabis plants. The most common type of mold is black mold, which appears as black spots on the leaves. Mold puts stress on the plant and can eventually kill it if left unchecked.

To get rid of mold, you need to increase air circulation in your grow room and make sure the humidity is below 60%. You can also use a fungicide to treat mold growth.


There are many reasons why cannabis leaves curl, and unfortunately, most of them are connected to problems with the plant. If your plants are healthy and well-cared-for, however, curling leaves may be due to overfeeding or temperature stress. Be sure to check for pests and powdery mildew as well, as these can also cause leaves to curl.

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