Cannabis Plant Leaves Curling Up or Down: Causes and Solutions

Cannabis plant leaves curl upwards or downwards for different reasons, and the solutions to each condition are also different.

Firstly, the leaves of your cannabis plants will generally curl up as a way of reducing excess transpiration. This is especially common in younger plants. 

In younger plants, the roots aren’t quite strong, so the water supply to leaves is not at its best. The leaves, therefore, rollover (or curl upward) in an attempt to reduce the surface area available to the sun. This initiative prevents too much sunlight from touching the top surface of the leaf, which is known for photosynthesis.

Now, on the other hand, when your cannabis leaves are curling downwards, it indicates more profound issues relating to nutrient deficiencies or viral infections.

This article will discuss the causes of each of these observations in detail and offer solutions that will work for you.

Key Takeaways

• Check to confirm if your leaves are curling up or down. The solutions are different.
• Low humidity is a common cause of an upward leaf curl, particularly in younger plants, where the roots aren’t quite strong yet.
• Excessive heat can also cause leaves to curl up as a defense mechanism.
• Both nitrogen toxicity and potassium deficiency can lead to curling, requiring careful nutrient management.
• Too much light, especially when it’s too close, can cause leaves to curl up or edges to burn.

Cannabis leaves curling up or down: What’s the difference?

Alt: picture comparison of cannabis leaves curling up or down

When cannabis leaves curl upwards or roll over to form some sort of tube, it’s an issue related to light and photosynthesis. And the good news is this isn’t a serious problem. 

Your plants are trying to reduce transpiration on the top surface of the leaves, so they roll over to try and expose the underside of the leaf to the sun instead. 

This is usually a temporary issue that goes away if your plants are generally solid, healthy, and well taken care of.

But when the leaves of your cannabis plant curl downwards, it’s scientifically proven to be a nutrient deficiency issue. And fixing these nutrient deficiencies (Mg, Ca, Cu, etc.) is how you deal with this problem before it eventually gets much worse.

In some cases of viral infections, you might even have to remove the infected plants.

Causes of Cannabis Leaves Curling Up

These are other common causes of your cannabis leaves curling up: 

1. Excess Light

Whenever light energy strikes the top of the leaf, it forces that plant to engage in photosynthesis, which results in transpiration (water leaving the leaves into the atmosphere). 

Ultimately, that’s how plants stay strong and can pull up an unbroken chain of water from the root zone into the foliage, which then evaporates into the atmosphere.

Alt: Cannabis plant off-rooted from the soil with visible white roots

When a cannabis plant needs to reduce its transpiration, it’ll shade itself and show the underside of the leaf to the light. This reduces transpiration. 

But why is this happening? Ultimately, it is because the root zone can’t keep up with the above-ground needs of water. 

For example, let’s say you have an 18-inch tall root-bound plant in a one-gallon pot, and you haven’t quite watered it enough. It’s drying out. If the light conditions in the room are intense but the root zone isn’t large enough to keep up with that, your plant’s leaves will start to curl upwards.

2. Plant Growing Rapidly Above Ground

Sadly, a plant that grows way too fast above ground could also run into this leaf curling issue. 

If your plant is growing so fast above ground and the root zone hasn’t fully developed yet, there will be a water supply problem. The root zone will not supply enough water to keep the entire plant in a state of photosynthesis, metabolism, and transpiration. 

The plant starts reducing its transpiration rate, which is common in plants that grow rapidly above ground and that can make the leaves curl up.

3. The Environment

Your cannabis plant’s leaves curling up (or rolling over) could also be related to the environment in which the plant is growing. If your outdoor or indoor grow environment is super dry, that could induce a rate of transpiration that the root zone can’t keep up with.

As a response, the leaves try to hide the top surface away from the sun (curling). 

4. Lights Too Close

If your indoor light levels are also too intense or perhaps your LEDs are too close to the plant, they get a little too hot. The intensity of the lights will burn or bleach the plant material. 

In response, the plant tilts the leaves and reduces its transpiration rate to protect itself from the light. 

Solutions for Fixing Cannabis Leaf Curling Up

Alt: Cannabis leaves curling up

Here are some of the solutions you can start implementing starting today to fix this leaf curl issue. 

1. Transplant and rebound the plant

Transplant the root-bound plant and apply some root stimulator to get that root zone to the point where it can take up enough water to supply the above-ground foliage with its requirements. 

In the case of a plant that is growing super fast above ground, as long as you’ve got it in the right pot size, you can also apply a root stimulator to balance it out. 

2. Get the correct-sized pot.

If you’re using a smaller pot, here’s how to get your plant into a larger pot. As far as pot sizes go, you should try to use a 5-gallon pot for plants that are 3 to 5 feet tall, or a 7-10-gallon pot for plants that are 4 to 6 feet tall. 

For plants taller than 6 feet, you can use a 15+ gallon pot.

If you’re currently using a very small pot for your cannabis plants, here’s how you can transplant them to a new pot without hurting them:

• Dig up the plant from its original container (or pot).
• Once you’ve removed the plant from its small container, assess the condition of its roots.
• Soak and untangle the roots.
• Cut into the root ball.
• Prune the roots.

You can now transplant it into a larger pot.

3. Humidifying the Grow Environment

If your garden is too dry, you can control the humidity with a humidifier. Evaporative humidifiers use a fan to blow air over a wet, absorbent material, such as a wick, that sends moisture into the air.

The humidity level of your grow space should not go below 40%; that’s your limit. You may aim for 55% to 70% humidity levels, and that should keep the environment moist enough to prevent excess transpiration.

4.  Adjust The light distance From Plants

If your plant’s lights are too close to the plants, you need to take steps to adjust that. 

During the vegetative stage, you can place your LED grow light further away from the plant, around 18-24 inches away. During the flowering stage, your grow lights should be closer, around 12-18 inches.

Causes of Cannabis Leaves Curling Down

When your cannabis leaves start to curl down, the situation is a little more complicated. You’re looking at issues like nutrient deficiencies or even pest attacks.  Below are the most common causes and solutions you can implement starting today:

Alt: Cannabis leaves curling down

1. Viral Infections

Viruses like the Beet Curly Top Virus have been reported to cause leaves to curl downward, thicken, and roll.

Besides the Beet Curley Top Virus, growers in Australia have also reported attacks from the Hop Latent Viroid (HLVd). Laboratory analysis of cannabis plants in Australia has shown that these viruses are present in a few farms in the country, causing cannabis leaves to curl in unusual ways.

True virus symptoms include alternating patterns of yellow and green (mosaic), yellowing on certain parts of the plant, or curling, distortion, and narrowing of young leaves.

 In addition, other abiotic stresses causing distortion or curling of leaves may appear similar to a virus disease. Stunted growth due to poor growing conditions may resemble a virus infection, especially if accompanied by foliar symptoms. 

Solutions to Viral Infections?

Experience suggests that simply removing symptomatic plants from your grow area helps the rest of the plants avoid the further spread of these viral infections that could cause serious damage to your cannabis plants.

2. Nutrient Deficiencies

The table below shows you a summary of symptoms, causes, and solutions for common nutrient deficiencies in cannabis plants.

Deficiency/Issue	Symptoms	Cause	Solution
Boron Deficiency	If your plants are showing symptoms of Boron deficiency, you will notice the leaflet margins become necrotic and the leaves severely distorted, curling inward and down and at odd angles from the petiole.  These symptoms first appear on younger tissues, as curled leaves that become thicker with age.	B-deficient plants had 96% lower amounts of Foliar-B, which explains the symptoms observed.	Aim to give your plants 58.58 mg·kg−1 Boron to curb this deficiency.
Copper (Cu) Deficiency	Leaves, particularly new growth, will develop a dark blueish-green color and show signs of wilting. With time, leaves become chlorotic and begin to curl. Blueish-green leaves that are beginning to curl are symptomatic of early stages of copper deficiency. In the most advanced stages, the whole leaf may display fine interveinal chlorosis, and the leaf margin may be distorted, slightly curling in and downward.	Cu-deficient conditions. Deficiency-treated plants contained 1.41 mg/kg Cu.	Copper is important in cell wall metabolism. Cannabis requires greater quantities of Cu (aim for 4.65 mg kg−1).
Beet Curly Top Virus	The leaves thicken and roll upwards.		Remove symptomatic plants from fields.
Potassium (K) Deficiency	Initial symptoms develop as a yellowing of the leaf margin, especially the sawtooth of the leaflets, on the lower and older foliage. Plants grown in K-deficient conditions weigh 27% less than regular plants. Leaves curled downward, the leaflet margins yellowed, and some regions of tan necrosis are all signs of K deficiency.	Symptoms of K deficiency develop	Monitor and ensure adequate potassium levels to prevent older leaves from curling downwards. Aim for a range of 1.83–2.35% of potassium for your plants.
Molybdenum (Mo) Deficiency	You’ll notice the curling or deformity of younger leaves, which is commonly referred to as ‘whiptail’ in many plant species.	Leaves displaying cupping and rolling due to molybdenum deficiency (96% lower Mo).	Check and adjust Mo levels in your plants if you notice symptoms. Aim for 1.46 mg kg1 of molybdenum.
Magnesium (Mg) Deficiency	Leaf curling is a common feature of magnesium deficiency. Late development of magnesium deficiency symptoms will show lower leaves that are necrotic and curled.		Investigate and adjust magnesium levels to prevent leaf curling and necrosis in lower leaves (aim for 0.61% of magnesium).

FAQs About Cannabis Leaf Curling

These are the most common questions from growers.

What Should I Do If My Leaves Are Curling During Flowering?

If your leaves are curling up during flowering, they’re probably fighting too much light. If you’re growing indoors, reduce the light intensity by shifting the LEDs further away from the plant.

Can Leaf Curling Be Reversed?

Yes, leaf curling can be reversed with the right solutions. For upward leaf curling, the simple solution would be applying a root stimulator, transplanting to a bigger pot, using a humidifier to humidify the air, or adjusting the light distances (18–24 inches) to reduce the light intensity in the younger stages.

For leaves curling downwards, simply address nutrient deficiency issues.

How can I prevent leaf curling in outdoor plants?

Yes, by providing sufficient nutrients (magnesium, calcium, boron, and copper) and providing the right quantities of water for your cannabis plants.

Conclusion

When your cannabis leaves are rolling over or curling up into tubes, you should know that it’s not the greatest problem in the world. And as long as you take the necessary steps to correct this imbalance, it will grow out of it in no time at all. But when the plants curl downwards, you need to look into nutrient deficiencies.

Why not start your cannabis cultivation with quality seeds you can trust? Shop for your seeds at Aussihemp, trusted by Australia’s top growers.