First grow problem – Edges of leaves are curling up?

Question: What do I do if the edges of my cannabis leaves are curling up?

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Edges of leaves are curling upThis marijuana leaf shows the problem. I think this may be humidity problems, but I'm not sure. What do I do?

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.


Answer: Heat stress, Root Problems or Extreme Humidity

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.

This cannabis plant is suffering from root problems plus heat

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.

Learn More About Cannabis Heat Stress

Learn More About Root Problems

Learn About Controlling Humidity



Jump to…

Leaf tips turned down? It may be a Nitrogen Toxicity
How to Set Up / Vent Heat with HID Grow Lights
Check These 7 Things & Cure 99% of Marijuana Growing Problems
1st Grow in My Garage – Auto Northern Lights in Grow Box Under 400W HPS





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