Why are my cannabis leaves curling up or down?

If you notice the leaves of your cannabis plants curling up or down, it is normally a sign that the plant is stressed. This could be for many reasons from root issues to overfeeding, so it is important to understand what you are looking for so that you can spot the subtle differences between each issue and identify the problem. Keep reading to find out the problems, how to identify them and most importantly how to fix cannabis leaf curling.

Possible causes for cannabis leaves curling up

Cannabis leaves curling up is a sign of plant stress that is most commonly caused by heat stress, overwatering, nutrient imbalances, and pest infestations. Each issue affects the plant differently, but results all cause the leaves to curl up, read on to identify the problem and solution.

Heat stress

Heat stress occurs when your cannabis plants are exposed to extreme heat, this can happen if you are growing indoors or outdoors. The most common cause of heat stress for indoor growers is if your plants are too close to your grow lights. The intense heat from the lights then causes the leaves to curl up as a protective response to conserve moisture. This prevents the plant from being able to absorb as much light and eventually it will lead to stunted growth.

How to fix:

To fix heat stress, adjust the height of your grow lights to ensure they are not too close to the plants. The ideal temperature for cannabis plants is 70-85°F (20-30°C) so get a thermometer, place it in your grow room and make sure you keep it within this range. Additionally, improve air circulation with fans to disperse heat evenly and keep the growing environment at a consistent temperature.

If you are growing outdoors and the weather is consistently above 85°F (30°C), preventing heat stress can be a little bit trickier. You will need to do whatever possible to bring the temperature down, this could include, bringing plants indoors or in the shade during the hottest periods of the day, watering them at nighttime, using fans to create a breeze or putting up a shade sail to protect them from direct sunlight during the hottest parts of the day.

Root problems

If there are any root problems preventing the plant from absorbing water, this can cause the leaves to curl up. Common root issues include root rot from overwatering, compacted soil that restricts growth, and a lack of oxygen in the soil. These will all hinder your plant's ability to take on water and nutrients and will eventually lead to dry curling leaves and stunted growth.

How to fix:

First you should make sure the soil or medium you are using is draining well, if it isn't you might need to amend the soil with something like perlite to improve aeration. Avoid overwatering your cannabis plants by allowing the top layer of soil to dry out between watering sessions. And lastly you might want to consider using pots with good drainage and aeration such as air pots or smart pots. If you suspect that your plants could be suffering from root rot, you will need to gently remove the plant, trim away affected roots, and repot it in fresh, clean soil.

Dry Climates

Dry climates and low humidity levels can cause rapid water loss through the leaves, leading to dehydration and stress which normally exhibits with yellowing leaves or leaves that curl. This environmental condition is common in indoor growing setups if you don’t keep on top of humidity control.

How to fix:

Fortunately, this is a relatively simple problem to fix, first get yourself a humidity monitor and thermometer and stick it in your grow room. The ideal humidity range is 40-60% so keep within this range. To increase the humidity, place a humidifier in your grow room. Another method is to water your plants just after your grow lights have turned off – this will allow the plant to absorb water during the cooler dark periods before the lights come back on. You can also regularly mist the plants with water to provide additional moisture and ensure proper ventilation to avoid mold and mildew developing.

Overwatering

If you overwater your cannabis plants the roots can become waterlogged and which will effectively suffocate them and stop them from absorbing oxygen. The early signs will be that the leaves start to curl, however, this can also lead to root rot.

How to fix:

You should first ease back on the watering and make sure the soil has had time to dry out enough between each feeding. Try using pots with good drainage such as smart pots that are made of a breathable fabric, this will prevent water from pooling at the bottom. Check the soil is dry enough before watering your plants again by sticking your finger about an inch into the soil; if it feels dry, it is time to water, if its damp allow one more day.

Too many nutrients

If your cannabis plants have more nutrients than they can process, it can cause a buildup of excess salts and nutrients in the soil. The plants can suffer from nutrient burn which causes the tips to turn brown and appear burnt, the leaves will also start to curl up.

How to fix:

To fix nutrient burn, flush the soil with clean, pH-balanced water to wash away excess nutrients. Once your plants have begun to recover reduce the frequency and amount of nutrients you add into the water.

Wind Burn

If your cannabis plants are exposed to strong, constant airflow, this can cause wind burn which will make the leaves to curl and develop a leathery texture. This happens because the excessive wind strips away moisture from the leaves faster than the plant can replace it, leading to dehydration and stress.

How to fix:

If you are growing indoors then you need to adjust the position and intensity of fans in your grow area. Ensure that the airflow is gentle and indirect, providing adequate circulation without directly blowing on the plants. You can also use oscillating fans to distribute air evenly.

If you are growing outdoors, then try putting up a wind shield around your plants to protect them from the strong winds. You still want some wind to blow on your plants, but simply by sticking a few bamboo sticks in the ground with some scaffold or wind breaker mesh around them will decrease the intensity of wind but keep enough airflow coming through to keep your plants healthy.

Possible causes for cannabis leaves curling down

If the leaves of your cannabis plants are curling down this could be a sign of overwatering, nutrient burn, or pest infestations. These issues disrupt the plant’s natural processes, leading to visible stress symptoms like downward curling leaves.

Excessive humidity

Excessive humidity can cause cannabis leaves to curl down as the environment becomes too moist for the plant to transpire properly leaving the leaves looking droopy or wilted.

How to fix:

Get yourself a dehumidifier and a humidity monitor and try to keep humidity between 40-60%. If you are growing indoors, you should also try placing some fans in your grow tent and use an extraction system to help reduce moisture build-up and improve ventilation.

Overwatering

When the soil is constantly wet, the roots of your cannabis plants will be unable to get enough oxygen, this will cause the leaves to droop and can eventually lead to root rot and other related issues.

How to fix:

To fix overwatering, allow the soil to dry out completely before watering again. Ensure your pots have good drainage to prevent water from accumulating at the bottom. Check soil moisture by inserting your finger about an inch deep into the soil; if it feels dry, it's time to water, if not then leave it a day or two more.

Temperature too high

High temperatures can cause the leaves of your cannabis plant to curl down as the plant tries to protect itself from the extreme heat.

How to fix:

If you are growing indoors regulate the temperature in your grow area to stay around 70-85°F (20-30°C). To do this you can use fans and air conditioning to cool down the environment if necessary. Ensure proper ventilation to allow hot air to escape and cool air to circulate. Another simple solution is to time your light schedule with the time of day, so that your lights are off during the hottest part of the day but on at nighttime when it's coolest. If you are growing outdoors, then you will need to create a temporary shade for your plants or move them indoors if that's possible.

Too much nitrogen

Excessive nitrogen will lead to nutrient toxicity. This condition results in dark green leaves, clawing, and overall plant stress as it struggles to cope with the nutrient imbalance.

How to fix:

Flush your soil with pH-balanced water for 2-3 days to remove the buildup of nutrients. Then continue with normal feeding once they have recovered but reduce the amount of nitrogen that you are feeding them.

Pests

Pests can cause cannabis leaves to curl down as they feed on the plant's sap, causing physical damage and stress. Common cannabis pests include spider mites, aphids, and thrips, which can weaken the plant and lead to various growth issues.

How to fix:

To fix pest problems it's important to spot the issue early on so you should be regularly inspecting your plants for any signs of infestation. If you spot any pests use organic insecticidal soap or neem oil to treat the affected areas. Another more natural method is to introduce predatory insects such as ladybugs to help control the pest population.

FAQ

What is tacoing?

Tacoing is when the leaves of cannabis plants curl up in a way that resembles the shape of a taco shell. When this happens the edges of the leaves curl upwards, forming a concave shape. Tacoing is often a sign of environmental stress, such as excessive heat, low humidity, or intense light exposure.

What is the most common cause of cannabis leaves turning up?

The most common cause of cannabis leaves turning up is heat stress. This usually occurs when the plants are too close to grow lights, causing the leaves to curl upwards in an attempt to reduce exposure to excessive heat.

What is the most common cause of cannabis leaves turning down?

The most common cause of cannabis leaves turning down is if you have overwatered them. When the soil is consistently too wet, the roots become waterlogged and lack oxygen, leading to root stress and causing the leaves to droop and curl downwards.

What is the ideal temperature for cannabis?

The ideal temperature for cannabis plants is between 70-85°F (20-30°C) during the vegetative stage and 65-80°F (18-26°C) during the flowering stage.

What is the ideal humidity for cannabis?

The ideal humidity for cannabis plants is 40-70% during the veg stage and 40-50% during the flowering stage. Bringing the humidity down as the bud's form will help to prevent bud rot from developing.

Understanding how to spot these issues is vital if your leaves are curling up or down and showing signs of stress. Whether it's root problems, dry climates, overwatering, nutrient issues, wind burn, or pests, you now have the knowledge to diagnose and fix these issues. Don’t forget to like and share this article!