Why Are My Cannabis Leaves Curling Up

Cannabis leaves can curl up for a list of reasons, and it is often not one single culprit but a combination of multiple ones. That means we are talking about the whole picture. But if you are able to identify underlying causes clearly, you can fix cannabis leaves curling up more effectively. 

Regardless of which leaf curl you are faced with, here are the most common causes of cannabis plant leaves curling up:

Light Stress & Heat Stress 

When growing cannabis indoors, you are using grow lights - whether it’s an HPS or LED grow light, right? When the PPFD levels are excessively high for your cannabis scale or the lights are placed too close above the canopy, they create light stress. As a result, the leaves being exposed to strong light intensity get curled up to protect themselves. 

Along with the excessive light intensity comes the heat, particularly when you are running old-fashioned cannabis grow lights. The excessive heat emission burns your marijuana and causes cannabis leaves to curl inwards, especially the ones on the edges because they are generally closer to the light source.

Too High/Low VPD 

To introduce VPD (Vapour Pressure Deficit) in an understandable way, VPD impacts how well your cannabis is breathing and absorbing the nutrients. When the VPD is too high, the air is too dry, causing the plant to lose water rapidly. This rapid water loss forces the plant to curl its leaves upwards in an attempt to reduce the surface area and minimize water loss. 

Conversely, when the VPD is too low, the air is too humid, hindering the plant's ability to transpire effectively. This can lead to a buildup of moisture in the leaves, causing them to curl as well. How much VPD does the cannabis require? Use our online VPD calculator for precise control. 

Pest Infestations 

Cannabis plants can attract a wide range of pests such as spider mites, aphids, thrips, and whiteflies, which all feed on the plant's sap. These insects lay eggs and then accommodate on leaves, particularly on the underside of cannabis leaves. After sucking the sap from your leaves, these pests leave behind yellow spots on the leaves and a variety of symptoms.

For example, broad mites feeding on the cannabis plant often result in twisted leaves with a very shiny appearance. Other mite species may cause small yellow spots on the topsides of the leaves and even lead to brown and dying leaf matter. Although it can be hard to distinguish which mites cause the problem unless you catch them on the scene, all pests damage your cannabis leaves and stunt the growth of the plant for sure.

Nutrient Deficiencies

Cannabis plants require a wealthy niche of nutrients to grow and thrive, say, nitrogen, 

phosphorus, potassium (K), magnesium, calcium (Ca), etc. Deficiencies in any of these nutrients can cause the cannabis not to grow the way you expect. For example, a nitrogen deficiency can cause the leaves to turn yellow and end up curling up as they die, while a potassium deficiency can cause the leaves to appear burned and curled up at the edges. Notably, a cal-mag deficiency in vegging and flowering hurts the cannabis and causes the plant leaves to curl up or downward.

Nutrient Burn

In contrast to nutrient deficiency, overfeeding can also be a problem. Over-fertilized roots with excessive mineral content make it hard for your cannabis to remain optimized plant biochemistry, particularly during the flowering stage. To name one example, if your cannabis is given excessive nitrogen-rich veg nutrients, the leaves will turn dark and present a claw-like structure.

Incorrect pH Level

As a vital factor that affects the availability and uptake of nutrients by the plant, the soil pH level can easily affect your cannabis growth. If your plants are experiencing a low pH level, you can spot yellow-to-brown splotches on the upper leaves at first and finally curling up leaves at the end. For a high pH level, you may notice brown splotches taking over the whole leave.

Overwatering 

Overwatering is a common mistake that beginners make when growing plants. Excessive watering swells the cell, making it impossible for the plants to absorb enough water (completely the opposite way) and leading to drooping leaves that start to claw slightly. Additionally, the roots are suffering from inadequate aeration, which can negatively impact their health and overall growth.

For proper cannabis watering techniques, you may check this post: Ultimate Guide on Watering Cannabis: Best Time & How to

Extreme Temperatures

Cannabis plants are sensitive to temperature fluctuations, and extreme temperatures can cause the leaves to wrinkle and become crispy. High temperatures in the grow room (above 86 °F/30 °C) can cause the leaves to wilt, while cold conditions (under 55 °F/12 °C) can cause upward curling on the leaf tips, which happens particularly in outdoor growing.

Improper Humidity Level

Cannabis requires a specific range of humidity levels (somewhere between 40% - 60%, depending on the stage of weed growth) to grow and thrive. High humidity levels can cause the leaves to curl up and create an environment for moldy weed, while low humidity levels can cause the leaves to droop, with the leaf tips pointing down.

Wrong Soil 

If you prefer soil growing over hydroponics, the choice of soil matters. When choosing the ground for your cannabis, pay attention to the drainage, water retention, nitrogen content, and texture. For instance, soil that has bad drainage could result in waterlogging, which can lead to root rot, and therefore damage your cannabis growth.

Genetic Natures

It’s not always your fault. As breeders continuously produce new cannabis strains, some of the new species come with different manifestations that include a curled leave. So, if you are planting any new cannabis mutations, perhaps one of their signatures is the clawing leaf and it’s actually not a big deal. 

How to Cure Cannabis Leaves Curling Up [5 Key Methods]

Reading so far, you know what causes cannabis leaves to curl up, the question now becomes how to fix cannabis leaves curling up or down? In the following content, 5 major methods are included to help you regain flat, open, and vibrant cannabis leaves. Read on to find out how. 

Provide Proper Lighting

As mentioned earlier, if you spot fan leaves curling up on the edges, it’s likely the intensive lighting is harming your weed. Compared with traditional HPS bulbs, LED grow lights can produce less heat, adjust light intensity, and are more energy efficient. To provide proper lighting for indoor marijuana growing, LED grow lights are better investments. 

The position of your grow lights is also worth thinking about - how far should LED grow lights be from plants? Generally speaking, it’s a good idea to place the grow light at around 12 to 30 inches from your cannabis, however, bear in mind that as your plants grow, the height should be adjusted as well. 

Grow Room Temperature & Humidity Control

To control the grow room temp: 

Use a digital or analog thermometer to examine the grow temp and make sure the temperature for growing weed stays between 68 - 78°F (20 - 25°C). If the meter goes beyond or below that, you can control the temp with a clip fan or air conditioner if available. 

To control the grow room humidity:

The humidity level is suggested to stay between 40 - 60%. For a low humidity level, you can raise the humidity in a grow tent in multiple ways. For budget-efficient growers, use a professional plant humidifier such as Spider Farmer Cool Mist Humidifier for Plants. If you are more into ways without a humidifier, you can place wet towels and sponges to increase the humidity.

If the grow room gets too moist, you should decrease the humidity then. You can explore our comprehensive guide on grow room temp and humidity levels for detailed help. 

However, if you are growing outdoors, the temperature and humidity can be more difficult to manage. Some growers just stop planting ween during the hottest days of the year to avoid extreme conditions. 

Maintain the Right Soil Moisture

There are various means to cure overwatered cannabis and avoid cannabis plant leaves curling up in the future. 

• If you think the soil is already excessively watered, simply let it dry out for a few days. Then you can test the moisture level by pressing your fingers in the dirt. 
• For less experienced cannabis growers, it’s better to underwater the seedlings rather than overwater them. Just be aware that it’s OK to leave the plants unwatered for a day or two.   
• You can go for drip irrigation or use sprinklers with timers to better control the water amount. 
• Use a soil moisture meter to make sure that the soil is moist but not waterlogged. 
• Switch to a highly aerated growing container that allows more oxygen to penetrate the root mass. In this case, your cannabis root is less likely to be suffocated by overwatering. 

Adjust Nutrient Levels

For already overfertilized plants, you can rinse the roots with water to clear out excessive nutrients. Then, follow the common principles for adjusting nutrient levels in your cannabis to the optimal outcome, no matter whether it’s nutrient deficiency or overfertilization. 

• It’s best to take organic nutrients such as soil or coco fiber instead of artificial ones. Although organic mediums release nutrients in a slower way, they can deliver the exact right amount that’s required by your plants and therefore prevent overfeeding or underfeeding. 
• Slowly and gradually add nutrients to your cannabis as it matures. It’s not suggested to use strong nutrients at first just to shorten the growth process. 

Eliminate Bugs

Inspect your cannabis plants for signs of any pests. If you find pests, you can control the situation by spraying the plants with a solution of neem oil, insecticidal soap, or using an organic pesticide to eliminate them. 

Verdict on Cannabis Curling Up 

Why do cannabis leaves curl up? Too much light, overwatering, overfeeding, unsuitable temperature and humidity, and bugs can all be the reason. Regardless of which situation you are in, this post covers 5 working solutions to help you effectively fix cannabis leaves curling up. Don’t hesitate to leave a comment below if you have any questions or thoughts! 

FAQs about Cannabis Leaves Curling Up

• Why are my cannabis leaves crispy and curling up?

The most common reason for cannabis leaves being crispy and curling up is heat stress. Whether it’s the heat emission from the grow lights or the high temperatures, excessive heat can cause the leaves to dry out and curl.

• Why are my cannabis leaves curling like tacos?

Heat stress and calcium/magnesium deficiency are two main factors that cause cannabis leaves to curl up like a taco. High temperatures can cause the leaves to curl up and turn yellow or brown at the edges, while a deficiency in calcium or magnesium can cause the leaves to become brittle and curl upwards like a taco.

• How do you fix curling leaves?

It’s best to spot the reason for your curling leaves before hands-on fixing them. Overwatered cannabis is one common cause, so you can stop watering for a few days to let the soil drain out extra moisture. Then you can resume watering with drip irrigation to avoid overwatering again.