Сannabis Leaves Curling Down: What Causes & How To Fix It?

“Help, my cannabis leaves are curling down!” is a common statement among beginners. 

Cannabis plants can't tell you when something's wrong, but they give various indications about how they feel. 

Every grower will experience such instances in his journey of growing cannabis. 

While some growers ignore those issues for various reasons, others get into the driver's seat and take charge of the situation. 

Some distress signals the plant sends can range from yellowing leaves to pest attacks or drooping. Whether your plant is dull or turning yellow or curling its leaves resembling a claw, the key lies in recognizing it and taking action. 

Cannabis leaves curling down or up is one of the most common problems you'll probably face. However, this doesn't translate to it being easy to cure if you're new to all this. 

Therefore, we will explore why cannabis leaves begin curling down and how you can prevent them the next time. In addition, we will provide solutions so you're a happy grower!

What Is Leaf Curling?

Leaf curling, as the name implies, is a condition where you'll see cannabis leaves curling. Now, they can curl either up or down, depending on what's bothering them. 

In short, the plant is stressed when it curls its leaves. 

Leaf curling occurs due to various reasons, from overwatering to using bad soil to genetics and it can be difficult to pinpoint exactly why it's happening. Therefore, it's best to prevent it rather than try to cure it. 

What Causes Curling Weed Leaves?

As mentioned already, weed leaves can curl up or down due to several reasons. Often, it's not possible to find out why. If you notice the leaves curling, go back to the basics and check everything. 

For instance, check if the pH is okay. You don't need to maintain a strict number but a range will suffice. For soil growers, a range between 6.0 to 7.0 will be perfect whereas hydroponic growers will have to maintain a range between 5.5 to 6.5 for the plants to do well. 

But, if the pH is okay, there may be other problems, which we will discuss below. 

1. Pests

Pests affect all kinds of plants and cannabis is no exception. Some pests like spider mites, hemp russet mites, fungus gnats, broad mites, and aphids are particularly fond of cannabis and attack them in various stages of their growth.

The problem is that you can't see these troublemakers easily; however, if you keep an eye on the plants, you'll be able to notice the effects on the leaves. You can't see aphids and spider mites on the leaves because they are usually found on the undersides where they suck all the nutrients.

As the aphids and mites bite into the tender tissues of the plant, you'll see weed leaves curling down. Another sign of a pest attack is that leaves become crispy and super dry. In addition, the stage at which they attack the plant is also very important. For instance, it is pretty easy to get rid of these pests if the plant is still in the vegetative stage; however, it becomes slightly more challenging if it's in the flowering stage.

The pest will slowly suck all the nutrition from the plant, whether it's a fan leaf or a stem, rendering it lifeless, and eventually, you'll see your marijuana leaves curling down. It's also common to see cannabis leaves twisting due to pests. If you ignore a pest attack you will see a drastic reduction in yields, and the plant may also die in severe cases.

2. Overwatering & Underwatering

Overwatering is one of the top reasons for marijuana leaves curling down. Many growers underestimate the effects of overwatering. In short, overwatering can drown the plant's roots and suffocate them, thereby killing the plant.

Overwatering comes with a host of issues. Not only will it deplete the plant of necessary nutrition but it also hosts mold and algae easily. If you frequently over-water the plant, you can expect problems such as root rot that makes the leaves droopy. You'll also notice the ends of leaves resembling claws.

On the other hand, underwatering can also cause the leaves to curl. If you notice the leaves are drooping and the top soil is very dry, then you can water a bit and see how the plant reacts. If the leaves perk up in a short period, then they were asking for water. If the leaves are still droopy even after a few hours, then the cause can be something else.

3. Using Too Much Fertilizer

Many beginners think that plants will grow better if they use as many fertilizers as possible. However, the opposite of this is true. If you use good soil and grow the plant organically you don't even need additional fertilizers. 

On the other hand, if you're growing hydroponically or going for a soil-less grow like coco peat, Rockwool, and whatnot, then you will need some fertilizers; however, you don't need too much to make the plant happy.

Have you ever noticed your cannabis leaves becoming dark green with claws at the ends? Or, your cannabis leaves twisting? It happens due to excess nitrogen also known as nitrogen toxicity. 

Similarly using excessive fertilizer of any kind including Phosphorus and Potassium during the pre-flowering and flowering stages will force the leaves to curl along with burnt tips. If you ignore the problem, the leaves will experience chlorosis before finally dropping off.

4. Bad Medium

Whether you're growing in a hydroponic medium or soil, it's important to make sure the medium is healthy. However, those that grow in the soil must be extra careful as it can get clogged easily.

Good soil is typically a mixture of coco peat, perlite, aged manure, and other substances that increase aeration. Without aeration, the roots get suffocated, especially if the soil is dry and muddy. Heavy soil will not get you good results.

If you notice that the soil tends to clump, then the leaves may begin to droop slightly. Many growers try to rectify this issue by watering the plants, but it's not very helpful as the root cause lies in the problematic soil. In addition, overwatering plants in heavy soil will cause mildew and other issues. The plant will not be able to absorb nutrients easily.

5. Windburn

Ever left a plant too close to the fan? It not only curls up the leaves but also makes the plant look unhealthy like it's having a rough time. Exposing your plant to strong winds is like a hurricane in an open field. Well, not really…but you get the idea. 

If the wind is too strong, the plant tends to curl up its leaves to defend itself. While this is very much possible outdoors, it can happen indoors too if you have powerful fans directing wind straight at the plants. 

Apart from leaf curling, windburn also causes dark spots on the leaves, giving them a burnt look. You might mistake it for some sort of deficiency but it's a natural reaction from the plant. 

6. Genetics

Sometimes, cannabis plants struggle to grow properly even if you've done everything right. Nothing is in your control if the genetics are not compatible. This is why you see weed leaves curling down or up for no particular reason. 

For instance, you can't expect great yields if genetics doesn't support it. Similarly, you can't get good clones from a sickly plant. Even if you clone them, it will pass on the diseases to the clones, wasting your time and effort.

Therefore, if the strain you're growing doesn't have good genetics, you can't do much about the curling leaves. If you're growing multiple plants with the same issue, genetics could be the culprit behind your cannabis leaves curling down, assuming they aren't suffering from some deficiency or pH imbalance.

Healthy plants produce healthy seeds and clones, and the converse is true for unhealthy plants. So, if your plant is genetically predisposed to fall sick with minimal stress, there isn't much you can do. However, you can increase nutrition to see if they respond well.

Truth be told, most forms of abnormalities you see in cannabis plants are usually due to genetics. Some strains tend to display abnormalities from the very moment they germinate, whereas others may take a while to do so.

7. Light Burn

Cannabis plants grow well if you provide optimal lighting conditions. Many growers assume that the more light they get, the better the plants grow. Yes, they need a lot of light, but if you use a 1000w HPS light in a small closet, you're going to have issues.

If you place super-powerful grow lights in small grow tents or rooms, the plants will experience light burns. Also, they will suffer from heat stress as the lights will emit quite a bit of heat. Although you can reduce the heat a bit by installing LED lights that don't produce a lot of heat, the plants can still fall sick if the lighting is too much.

Cannabis plants display curled leaves even if the lights are placed too close to them. One way to identify this is to check if the tips of the plant are curled. If the rest of the plant is doing fine, it's probably light burn. You'll also see those curled leaves develop burnt edges — a classic sign of light burn. Other symptoms include yellowing of the leaves. The leaves eventually die and fall off.

8. High Temperatures

Like light burn, heat stress also takes a major toll on the plant. And it does not apply only to indoor growers as the plants will struggle even if you reside in a hot area and grow them outdoors.

Typically, the leaves will start curling at first. The tips will also turn brown or crispy, indicating they are burnt. Imagine living in a sauna 24/7. Can you manage that? No? The plants can't do it either.

9. Cold Temperatures

Many growers reduce the temperatures intentionally to bring out the colors of the buds. For example, purple strains turn a deep purple-blue when they are exposed to cold temperatures. However, one needs to do this gradually in the late flowering phase to avoid shocking the plants.

In addition, don't expose the plants to cold temperatures for long periods. Doing so will result in curling leaves as the plants will not be able to handle the cold. 

The leaves will also begin to turn yellow and die eventually, leaving you with less yield if the plant survives until harvest. If you manage to harvest the buds, they will be almost soggy and vulnerable to diseases like bud rot.

Tips For Reducing and Stopping Weed Leaves Curling

Now that you know the causes of cannabis leaves curling, we will explore a few tips that will help you prevent the problem in the first place. You can follow these methods even if the leaves have already begun curling.

1. Stop Overwatering and Underwatering

Water is very important for the cannabis plant but too much of it or too less of it can be bad. Water helps the plant absorb nutrients, and develop stronger leaves, stems, branches, and fat buds but the moment you water too much it all goes haywire.

Remember that it is always best to water in moderation because you cannot expect the plant to survive if you water too less either.

It's very easy to correct both overwatering and underwatering. First off, follow a proper schedule rather than randomly watering the plants. The plants won't need too much water during the vegetative and seedling stage compared to the flowering stage. 

You will notice that the plant becomes more hungry during the flowering stage which is when you need to water it more or increase the frequency.

Before watering, check the soil to see if it is dry by inserting your finger into the soil. If it's dry for at least 1 inch then you can go ahead and water it. 

Another method is to pick up the containers. If the containers are light, then you can water the plants, but if you feel they are very heavy, you can wait for some more time before watering them. 

You can also invest in a moisture meter that tells you exactly when to water. A moisture meter checks for saturation levels from the very root of the plant.

To correct overwatering, allow your plant to rest for a few days before watering again. Make sure you use containers with a lot of holes that allow the water to drain out. In addition, use loose soil so that it doesn't get waterlogged. The best way to grow cannabis plants is to use fabric pots that drain the water very easily.

If you've corrected overwatering issues and waited a while for the plant to recuperate but still notice that the leaves are curled, then you'll have to transplant it into another pot to avoid more issues.

2. Reduce Nitrogen

Canvas plants need a lot of nitrogen in the vegetative stage but it's easy to get carried away and overload with nitrogen. Excess nitrogen will force the leaves to turn an unhealthy dark green and slightly waxy. Consequently, the leaves will start curling and take on the shape of a claw.

To prevent this problem, keep a close eye on your plants and observe how they react to their first dose of nutrients. If the leaves appear extra green, you can cut down on the fertilizers during the next week. If it is very light green, then you can increase the amount of nitrogen — commonly called grow booster — during the next week of feeding.

It's safe to follow the manufacturer's guidelines while providing nutrition to your plants but if you want to apply only nitrogen you can try organic sources such as coffee grounds, and rabbit and chicken manure for a boost of nitrogen.

3. Stop Over-fertilizing the Plants

Many growers over-fertilize their plants in the hope that they grow strong and study; however, less is more when it comes to fertilizing your plants. For instance, adding slightly extra phosphorus during the pre-flowering and flowering stages will lead to fatter buds. 

The same goes for potassium as well, but this doesn't mean that you add more than the recommended dosage of the manufacturer as it will result in the leaves curling down and looking like claws.

If you want to provide only one type of nutrient, such as potassium in the flowering stage, you can go for organic sources like banana peels that will not hamper the plant in any way. For extra phosphorus, you can add wood ash but use small amounts as it can alter the pH if used in excess.

It's a good idea to use less than recommended to prevent problems. You can adjust the feeding as required later, depending on how the plant reacts to it. Also, not all plants require the same feeding. Some plants can be very hungry whereas others need very little to grow healthy.

4. Windburn

Windburn is pretty easy to cure. Simply reduce your fan speed or point them in a particular direction where all the plants get adequate airflow. You can even consider downgrading your fans if you've purchased something too powerful for a small grow tent or room. 

Once you do this, allow the plants to rest for a while after watering them. Excessive wind will make the soil dry up too soon, so check if the plants are underwatered. 

For indoor growers, controlling the ventilation is easy, but it is not the same for outdoor growers. If you're growing outdoors you can use barriers or fences to reduce the wind flow a little bit or you can use green shades. Indoor growers can regulate the airflow by placing the fan in such a way that it does not blow directly over the plants.

5. Lightburn

Light burn usually happens if the plants are placed too close to the lights. You can rectify this problem by applying training methods like LST so the plant does not get too close to the light. Or you can pull the lights slightly far away to prevent issues. 

If your plant still experiences a light burn, check the intensity of the lights and choose appropriate ones according to the size of your grow room.

Make sure your lighting equipment is suitable for your grow room. For instance, you can use a 250w HPS light for about 2 plants whereas a 120w LED light is suitable for one plant. 

An average of 100-120w per plant will do. Although you don't have to stick to a specific number when it comes to wattage, you can maintain a range so the plants receive enough light and are happy. Suffice it to say that you need to calculate light requirements according to your grow room before buying the lights.

6. Prevent Pests

You can always expect pests to come in search of cannabis plants. Various pesticides on the market can be used to get rid of aphids and spider mites easily. You can also prevent this problem by spraying neem oil, soap, and water solution so the insects stay away. 

If the plant is affected during the flowering stage, gently remove the affected parts and spray with Spinosad or any other pesticide that does the job well.

7. Genetics

Always buy seeds from reputed seedbanks or breeders to avoid growing plants with genetic abnormalities. In addition, check out the reviews from various users so you get an idea of how the plant performs.

Most seedbanks will provide all the information regarding the plant. Sure, they won't announce "hey, these seeds have genetic issues" but the users will usually point them out. Trustworthy breeders test their seeds numerous times to ensure their customers are happy. Also, such seeds are usually removed from their catalogs to prevent problems.

If you intend to clone plants, always check if the mother plant is healthy. Naturally, if the mother plant has a history of abnormalities, don't bother cloning it. Even if you're purchasing or getting a clone from a dispensary or a generous friend, ask if the plant has any problems.

8. Prevent Hot and Cold Temperatures

Cannabis is a hardy plant but likes cool temperatures — not too hot and neither too cold. High temperatures can not only harm the plants, but they decrease the yields to a great extent too.

Cannabis pretty well between 68°F to 77°F (20°C to 25°C) during the vegetative stage and 65°F to 85°F (18°C to 29°C) during the flowering stage. 

You'll face problems if the temperature exceeds 86°F or goes below 59°F. When the temperatures are normal, the leaves appear healthy and green. However, they will lose their sheen, become dull and begin to curl if the temperatures are not in the right range.

To prevent heat stress, maintain the temperatures. You can use air coolers or air conditioners to regulate the temperature. If you're growing outdoors, however, read about the optimal time to sow and grow seedlings and follow the calendar. You can also use green shades to protect the plants from stress.

Therefore, use an air conditioner or even a cooler if the temperatures are too high. The cooler, however, will increase humidity so keep that in mind.

Indoor growers can regulate their grow room temperatures to avoid extreme cold. You can add a heater inside the grow tent or use an air conditioner to increase the temps. Adding extra grow lights will also raise the temps.

If you're growing outdoors, try relocating the plants at night if the temperatures dip below 50°F or 10°C. Or, you can again follow the growing calendar to figure out when the temperatures are optimal for growing cannabis.

9. Use a Good Medium

Always prepare your soil beforehand when planting cannabis plants. Bad soil can lead to water clogging and the plant may also develop root rot or bud rot.

Good soil is something that doesn't drain too much of the water and doesn't retain too much either. It should be in between.

If the soil is very bad, it's best to transplant the plant into another container with fresh soil. Make sure the new soil is loose. You can also add perlite to increase aeration.

Always test the soil for its water retention capabilities by pouring some water on it beforehand. If it drains well, you're good to go; however, if the soil struggles to drain water, and you see the water pooling around the top for a while, you may need to replace it or aerate it more. Good soil helps the plants retain as much water as possible, but it won't suffocate the roots and reduce oxygen levels.

Conclusion 

Weed leaves curling down or up can upset you as a new grower but there are various ways to prevent them, as discussed in this article. It's also common to see your cannabis leaves clawing. 

In addition, ensure that the pH is in range before looking at other possible issues. 

Most importantly, use good soil with lots of organic matter. If you're growing in hydroponics, follow the other tips we have mentioned. Cannabis leaves curl up when they are under stress, but they perk back up when things get back to normal. The key is to understand the problem and decide your course of action. 

FAQ 

Why is my weed leaf curling up?

Weed leaves curl up due to a variety of reasons including high/cold temperatures, nitrogen toxicity, stress, light burn, and more. 

Why do weed leaves curl down?

Weed leaves usually curl down when there's overwatering/underwatering, overfertilization, and heat stress.  

Why are my weed leaves folding like a taco?

Typically, cannabis leaves fold like a taco when there's either a calcium or magnesium deficiency, humidity and heat stress. 

Why are my plant leaves curling down?

The cannabis plant leaves could be curling down due to overwatering and underwatering. 

Can weed plants get too hot?

Yes, weed plants can get too hot if the temperatures in the grow room exceed recommended temperatures. 

Can the curled leaves go back to normal?

Yes, fortunately, leaf curling is curable and the plant will resume its normal state once you've identified and corrected the problem.