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 happen for many reasons, from root issues and a grow space that is too hot or too cold to insect infestations or overfeeding. 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 quickly.
Keep reading to find out what causes cannabis leaves to curl up or down, how to identify each issue, and most importantly, how to fix cannabis leaf curling so your plants can return to healthy upward growth.
Key Takeaways
- Humidity levels during 12/12 should be between 40-50%
- Heat stress is the most common cause of curling cannabis leaves
- Overwatering can cause the leaves to wilt and claw downwards
- Underwatering can cause brittle and curling leaves
- Heat stress and too much light will cause leaves to tacoe to reduce light intake
- Insects such as thrips, aphids or spider mites may produce curling leaves
- The optimal temperature during 18/6 is 70-75°F (20-24°C).
- The optimal temperature during 12/12 is 71-75°F (22-24°C)
- Humidity levels during 18/6 should be between 60-75%
Possible causes for cannabis leaves curling up
Cannabis leaves curling up is a sign of plant stress, most commonly caused by heat stress, overwatering, nutrient imbalances, or pest infestations. Each issue effects the plant differently, but all results 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, and especially during the hot summer months
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 as they need 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 70-75°F (20-24°C) so get a digital hygrometer , place it in your grow room and make sure you keep it within this range. Additionally, improve air circulation with fans or get a new extractor 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 (12-4pm) watering them after sunset, using fans to create a breeze, or the most effective is putting up a shade net to protect them from direct sunlight during the hottest parts of the day.
Actionable Tip: Compare leaf shape, temperature, humidity, and root-zone conditions before treating the problem so you fix the actual cause.
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.
You might want to consider using pots with good drainage and aeration such as air pots or smart fabric pots. If you suspect that your plants could be suffering from root rot, you will need to gently remove the plant, trim away effected roots, and repot it in fresh, clean soil.
Actionable Tip: Use well-draining soil and let the top layer dry slightly between waterings to keep roots healthy and oxygenated.
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, and can result in the leaves becoming thin, brittle and crispy to touch.
How to fix:
Fortunately, this is a relatively simple problem to fix, get yourself a digital hygrometer and stick it in your grow room. The ideal humidity range is 60-70% during the vegetation period, and between 40-50% during bloom, so keep within this range.
To increase the humidity, place a humidifier in your grow room and keep it on throughout the day. 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 and a spray bottle to provide additional moisture.
Overwatering
If you overwater your cannabis plants, the roots can become waterlogged, which reduces oxygen levels in the soil. Soggy soil also is a breeding ground for harmful bacteria. The early signs will be that the leaves start to curl, however, this can also lead to root rot.
How to fix:
The first thing is to let the pots and soil become almost dry. Then you should first ease back on the watering using less water than before 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 and the sides of the pot; if it feels dry, it is time to water, if it's damp and wet allow one more day.
Too many nutrients
It can be a common mistake to over feed your plants, and 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 as a sign there is a pending issue.
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. Gradually increase the strength of the nutrient solution once you notice the plants have recovered.
Wind Burn
If your cannabis plants are exposed to strong, constant airflow, this can cause wind burn which will make the leaves 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. This is very common outdoors during the summer season.
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, placing one on the ground and another higher up.
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.
This will decrease the intensity of wind but keep enough airflow coming through to keep your plants healthy. This is a cheap and highly effective method to protect outdoor cannabis plants from wind stress.
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 60-70% during 18/6 and 40-50% during 12/12. If you are growing indoors, you should also try placing some fans in your grow tent and using an extraction system to help reduce moisture build-up and improve ventilation.
Actionable Tip: Use a dehumidifier and proper ventilation to keep humidity in the correct range during both veg and flower.
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 longer until the soil is close to dry and dusty.
Temperature too high
High temperatures can cause the leaves of your cannabis plant to curl down or the leaflets to curl inwards, 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 70-75°F (20-24°C). To do this you can use fans and a top quality extractor 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. So this means during 12/12, you set the timer to come on at 9pm at night and to turn off at 9am. 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 overly dark green leaves, clawing leaf blades, 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 on a daily basis for any signs of infestation. If you spot any pests use organic insecticidal soap or neem oil to treat the effected 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 blades 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 70-75°F (20-24°C) during the vegetative stage and 71-75°F (22-24°C) during the flowering stage.
What is the ideal humidity for cannabis?
The ideal humidity for cannabis plants is 60-70% 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!
