by Nebula Haze
The following symptoms are for when your cannabis leaves are "clawing" or curling up or curling down. 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 an 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.
Bad Soil / Overwatering / Underwatering
You can help prevent over and under-watering your cannabis plants by always starting with good soil or coco coir.
When soil is thick and muddy, plants will be droopy (often with unhappy curly leaves) no matter your watering practices.
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!
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
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
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 or russet 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.
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.