Why Cannabis Leaves Curl and How to Fix them: A Guide for All Growers

Curling leaves on your cannabis plants can be an alarming sight to inexperienced growers. An experienced grower will consider it a good indicator of plant health. There are a variety of reasons why this issue can occur and leaving it untreated can affect the size and quality of your final yield.

This short guide is mainly geared toward indoor growing but the concepts can help outdoor growers understand similar problems. Let us equip you with all the knowledge you need to swiftly identify and deal with the underlying reason for leaf curling. To begin, let’s take a look at why a cannabis plant’s leaves can become curled in the first place.

Why are my cannabis leaves curling up and looking crispy?

First things first, don’t jump to conclusions as to the cause of curling leaves. Even if you think you’ve found the problem, go through the list and make sure that more than one of these situations applies.

Overwatering of cannabis plants and root rot

The most common problem that affects novice growers is watering their plants too much. Root problems generally start with overwatering since they need oxygen to stay alive. This primarily affects young plants that are grown in the soil since it holds the moisture within.

Roots that don’t get enough air will suffocate and die or pick up a disease like Pythium (root rot) which turns the roots into mush.

If continued unchecked, the soil will develop algae and other fungi that will completely kill your cannabis plant. Once these issues appear, they are difficult to get rid of so the best medicine, in this case, is a preventative one.

Overwatering does more than affect the roots though, with more water comes added humidity. If you have humid air during the flowering stage, moisture can get trapped inside the flowers and promote bud rot, making them unusable.

If you’re growing your marijuana plants in a hydroponic setup you won’t have to worry about this problem since the water gets the oxygen from the aeration inside the reservoir. For a more in-depth look, check out our article on growing hydroponic marijuana.

Soil problems

Soil needs good drainage, texture, and water retention abilities to be effective for your plants. Without good drainage, the watering schedule will fail as the excess water stays locked in the soil.

Additives like perlite will create spaces in the soil for water to drain easier while also holding in moisture for longer spans between watering.

The soil should be black with a nice loose texture. Cannabis roots like some resistance when they are stretching out. Too much resistance and they will have a hard time expanding.

Overnutrition

Nutritional balance is the key to effective cannabis growing, and pushing it too far can cause your fan leaves to curl up.

In the vegetative stage, your cannabis plant needs a lot of nitrogen, however, if you give it excess nutrients, then there is a chance for toxicity to occur. Nitrogen toxicity shows in plants as curly leaves and brown tips in the early stages.

Don’t stop there, if you want to learn more about growing cannabis with proper nutrient ratios and how to avoid using excess fertilizer, then check out the cannabis fertilizer guide we have posted.

Bad genetics

Unstable cannabis genetics can lead to all kinds of wonky effects during the growth cycle. Abnormalities like an oddly shaped cannabis leaf or curling weed leaves are common results of incorrect breeding. High-quality genetics remedy this problem since the strains have been grown and tested several times before being released onto the market.

If you start to see your weed leaves curling, the best remedy is to just remove the affected parts.

Wrong lighting conditions

Indoor growers love to push their grow lights so that their cannabis leaves can get what it needs to deliver beautiful buds. Incorrect wattage, mounting height, and spectrum inconsistencies are all reasons to cause light and heat stress, which also manifests in curling cannabis leaves.

Light stress occurs if your lights are too hot or if they’re too close. Your marijuana leaves will curl as the water evaporates and the plant gets additional moisture to it. This can occur outside and in a greenhouse with direct sunlight if your plants are too young.

Heat stress or cold shock

Cannabis plants’ leaves are unable to photosynthesize if the temperature is above 86 degrees Fahrenheit. At this point, there is a problem with heat stress and they may suffer from chlorosis and turn yellow, eventually falling off or they may curl up and down depending on the extreme.

If your temperature gets too cold and drops below 50 degrees Fahrenheit and stays there for a long period, your plants will start to show leaf curling. This is because growth is stunted and the roots have stopped absorbing water.

Short bursts of adverse temperatures can be beneficial but prolonged exposure can be detrimental to trichomes and terpenes.

How to fix weed plant leaves curling up and drying out?

Simply looking at the leaves curling is not the only thing you need to look at. This is because curling leaves can have many reasons for happening. Once you’ve identified that your cannabis leaves are indeed curling, you need to look for additional observations.

If you notice leaf curling that is facing downwards, it could mean an overwater issue as the leaves start to get heavy and droopy, almost swollen in appearance. This is a sign to let your soil dry out so the cannabis roots can breathe again.

Of course, it could mean a variety of other issues as well, for more info, check out our piece on how to fix your marijuana leaves if they are curling down.

How to fix cannabis seedling leaves that are curling up?

What if your cannabis leaves are curling up? Well, this is a good indication of some sort of heat, humidity, or nutritional stress, such as a nutrient burn.

At the first sign of your leaves curling up, take a look at the humidity, heat, and light situation in your room and ensure that they are within range.

The next thing you should check out is your nutrient ratio as you might have to adjust a few things.

For example, if the bottommost cannabis leaves are curling up and you notice them getting lighter or turning yellow, then you could have a nitrogen problem. Fixing this involves checking the PH of your soil and ensuring you are feeding your plants enough nitrogen.

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Join our community of cannabis growers and share insights and tips for dealing with curled cannabis leaves!