First grow problem – Edges of leaves are curling up? Question: What do I do if the edges of my cannabis leaves are curling up? A friend suggestted 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 humidty in my grow tent, it was 36% so I’m not actually sure it’s actually too low. More grow details: 250W HID, 2x3x5 grow tent with 4″ inline fan. 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 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.
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 ventillation 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. (“The Claw”) 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 a Nitrogen toxicity is curled tips (“the claw”) A plant with a Nitrogen toxicity tends to be dark green all over. You’ll notice that the leaves further from the fan don’t have symptoms. You can help prevent over and under-watering your cannabis plants by always starting with good soil or coco coir. 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! 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.