First grow problem – Edges of leaves are curling up?
Question: What do I do if the edges of my cannabis leaves are curling up?
Only one of my 3 plants is having this issue.
A friend suggested that the issue may be low humidity.
I live in a dry area so the humidity in my house is normally below 20%. However, when I checked the humidity in my grow tent, it was 36% so I’m not actually sure it’s actually too low.
Any ideas of anything else I should check?
More grow details: 250W HID, 2x3x5 grow tent with 4″ inline fan. Northern Lights strain. Seeds germinated in rockwool and transplanted into 4-gallon smart pots w/ mix of peat moss and perlite. Fox Farms Nutrient Trio for nutes – following the dosing schedule but started with 1/2 doses for the first week. pH of water is 6.5-6.6 and runoff from pots tested at 6.4-6.6.
This looks like the result of excessive heat, root problems (possibly from overwatering) and/or suffering from extreme humidity levels (such as very high or low humidity).
When the serrated edges of marijuana leaves curls or tipped up like that, it’s often a sign of temperature stress, overwatering/root problems or extreme humidity levels. This plant was overwatered and living in high heat, which is what caused these symptoms.
When the problem is low humidity, the leaf will also often fold in the middle, like a taco.
What’s your temperature in your grow area? Is there a hot spot around these plants from the grow light?
You mentioned that this is happening to only some of your plants. If this is happening to the plants which are closest to your grow light, that’s a hint that the problem may be temperature related.
If your light is simply too close, you can move the bulb further away from these plants and this issue may resolve itself. However, these leaves are showing symptoms of heat stress, without light stress (burning/spotting), so it’s more likely that the light is a good distance away and the heat just isn’t being controlled properly.
If plants are also droopy, it’s likely you’re dealing with watering or root problems.
When growing with hot HID lights, good ventilation and an exhaust fan will go a long way towards preventing all these problems. If the whole grow area is too hot with stagnant air, you will want to consider venting out all that extra heat.
Having good air movement, like a small fan in your grow tent blowing over the tops of your plants, can help prevent hot spots from forming directly under your grow lights.
In general, if it’s too hot for you to be comfortable, it’s too hot for your plants.
[Answer inside!] Only one of my 3 plants is having this issue. A friend suggestted that the issue may be low humidity…
Why are Leaves Curling or Clawing? (“The Claw”)
The following symptoms are for when your cannabis leaves are “clawing” or curling up or curling down. Sometimes known as “The Claw”. I’ll give a short explanation with pictures of each problem, plus links to the solutions! Fix this common (but hard to diagnose) marijuana problem today!
A Nitrogen toxicity is the result of the plant getting too much Nitrogen (usually from too high levels of nutrients overall, or by using a Vegetative nutrient in the flowering stage). It causes dark green leaves and curled tips (“the claw”).
One of the main symptoms of a Nitrogen toxicity is curled tips (“the claw”)
A plant with a Nitrogen toxicity tends to be dark green all over
Caused by too much wind. You’ll notice that the leaves further from the fan don’t have symptoms.
Example of too much wind on your leaves
Bad Soil / Overwatering / Underwatering
You can help prevent over and under-watering your cannabis plants by always starting with good soil or coco coir.
Bad soil is usually thick and muddy. Plants in poor soil will droop (often with unhappy curly leaves) no matter your watering practices.
Avoid thick soil that stays wet for a long time and doesn’t drain well
Overwatering makes leaves fat with water, and they tend to curl down and droop
Overwatering (especially when combined with heat) can also cause leaves to curl up
This plant was grown in muddy soil, and the curling, unhealthy leaves kept getting worse and worse over time!
Underwatering causes symptoms that often look like overwatering, but you’ll know it’s underwatering if the plants perk up each time after you water them.
Although often caused by overwatering, once the roots are sick you’ll see symptoms for a little while even after you start watering your plants properly.
Unhealthy roots can cause all sorts of problems including curling and clawing!
Unhealthy Roots in Soil/Coco
This plant’s roots were damaged from being overwatered and too hot for several days. As a result, the leaves took on a strange, blistery appearance.
This plant suffered from heat combined with overwatering for several days. This damaged the roots and gave it this odd leaf curling.
Root rot is something marijuana hydroponic growers can suffer from if pathogens attack the roots. It is often triggered by heat and/or lack of bubbles near the roots.
Root rot can cause curling leaves and brown patches as well as sometimes other nutrient deficiencies
If a plant stays in the same container for too long, the roots will eventually start wrapping around the edges of the pot. This is known as being “rootbound” and causes symptoms similar to other root problems.
A rootbound plant has been in the same container for too long. Roots wrap around the edges and “choke” the plant.
Rootbound plants often droop, appear yellow, get nutrient deficiencies, and stay small. Even if you’re caring for them perfectly!
If you see tons of white roots when transplanted, that means the plant was in that container too long
When this happens, the main solution is to transplant the plant into a bigger container. Another solution is to grow in fabric pots or air pots. These types of pots let air in from the sides, killing the circling roots (“air-pruning” them) and prevents the plant from getting rootbound for months.
To help a rootbound plant, transplant to a bigger container with fresh potting mix
Or start with air pots or fabric pots in order to prevent plants from getting rootbound at all
If plants are experiencing a lot of heat, it can make leaves droop and/or curl. Some strains can handle a lot of heat, while other strains tend to droop when it gets warm.
Heat can cause leaves to curl up
Read more about heat and growing weed:
Plants can get light burn (sort of like a sunburn) even if the temperature is completely under control. The symptoms are usually concentrated close to the grow lights. Sometimes this can cause leaves to claw and curl downwards.
Light burn can cause the leaves closest to the light to turn yellow
Bugs & Pests
Often a bug infestation caused general plant unhappiness, but these are some of the most likely to cause curling or clawing leaves.
Usually, you can’t see broad mites because they live inside the plant. The main symptom of an infestation is strange leaf curling that is specific to this pest, as well as “wet” looking leaves.
Hemp Russet Mites
Hemp russet mites can also cause drooping and other strange symptoms, but the bugs are so small many growers don’t realize what they’re dealing with.
Hemp russet mites cause drooping and yellow mold-like growth on the tops of plants
A closeup of the hemp russet mites
Fungus gnats look like tiny flies buzzing around your topsoil. Although a few fungus gnats won’t really hurt your plants, a big infestation can damage the roots, causing symptoms similar to other types of root problems.
Learn about the various things that cause cannabis leaf curling or clawing, and get the solutions!