Whether your leaves are curling up, down, or inwards, we’ve got the most common causes of curling leaves, and how to solve them in both soil and hydroponic setups.
Healthy vs. Unhealthy Cannabis Leaves
The first thing you want to learn is how to identify healthy cannabis leaves vs not healthy cannabis leaves. A healthy cannabis plant will have vibrant green leaves that have no discoloration or splotches of yellow or brown on them. Healthy cannabis leaves can be various shades of green, from a medium green to a deeper green, depending on the strain. Below is an image of healthy cannabis leaves.
Unhealthy cannabis leaves may be yellow or brown in color, either a solid color or splotches/ streaks of discoloration. The leaves may also curl and become crisp to the touch.
If you notice several leaves on your plant taking on these traits, it’s time to do some research and try to resolve what's causing your plant to have damaged leaves. Your plant is trying to tell you something is wrong and it needs your help. Keep reading to discover what could be causing your plant to be unhealthy, and learn how to resolve these issues in both a soil or hydroponic setup.
What’s The Function of Leaves On A Cannabis Plant?
There are two different types of cannabis leaves, both having slightly different functions:
Want to see us make a cannabis fan leaf smoothie? Check out this video!
Want to see what you can make with sugar leaves? Check out our video on how to make Cannabis honey oil!
Top Reasons For Why Your Cannabis Leaves Are Curling
Certain pests such as spider mites may cause your leaves to curl. Spider mites feed on the juices inside the leaves. They pierce the surface of the leaf and feed on the liquid in the cells. Damage will first look like tiny yellow, brown or white spots on the leaf, and rather quickly it can spread into full leaves of yellow/ brown. Make sure to look out for webbing on your plant, as this is a common sign of spider mites.
Treatment in both a hydroponic setup and soil will be fairly similar. Spider mites hate water. One of the first things you can do to slow them down is to wet the leaves of your plant. You can do this by spraying it down with your garden hose, or placing it in the shower. Next, you need something stronger to kill them off. You can purchase a general insecticide from your local gardening store, or on Amazon. If you have cats or fish in your home, make sure to do this process outside or with the room door closed, and keep the door closed for at least 48 hours. Pyrethrin, the active ingredient in most insecticides is very toxic to them.
When growing indoors you’re much less likely to get pests. Since Grobo has a closed door with a high-quality door seal, it’s extremely unlikely you will get pests on your plant as the only way they can get in is when the door is open.
Overwatering/ Root Rot
Overwatering causes too much water to be in the soil, which results in the soil being clogged and oxygen is unable to reach the plant’s roots. When the soil and roots cannot receive any oxygen, it becomes the perfect environment for harmful fungi and bacteria to grow. That harmful bacteria and fungi cause root rot, which is literally the roots rotting in the soil or water. One of the most common pathogens that causes root rot is called Pythium. It was formerly classified as a fungus, but it is now considered a parasitic oomycete, in the algae family.
If the plant’s roots are rotting, they're unable to properly function. A common mistake new growers make is watering a plant with wet soil when the plant is drooping. The plant is acting like it’s dehydrated and needs water because it does! The roots are unable to uptake water due to the damage caused by root rot, so the stem and leaves will look like they need water. Below is an example of what a plant with root rot may look like:
If you notice your plant’s soil is still wet, yet the plant looks dehydrated, it’s time to pull that plant out of the soil and check its roots. If the roots are brown, mushy, or smell rotten, your plant has root rot. If your plant has root rot, you need to take action, it will not go away on its own, and if it gets severe enough your plant may die from it.
To cure root rot in soil, the first thing you want to do is remove all the damaged roots. Any roots that are not firm and white should be removed. These damaged roots will often slide right off the root bundle. Next, you want to use hydrogen peroxide to clean the roots. Hydrogen peroxide will bring oxygen back to the roots, killing off the bad bacteria/ fungi. After that, you should be left with a clean root ball that is ready to be planted again. Don’t reuse any of the soil your plant was previously potted in as it’s filled with harmful bacteria. Make sure to also sanitize the pot you’re using to ensure it’s also clean. You first want to rinse the pot out with water to remove any remaining soil particles, then spray it down with rubbing alcohol or hydrogen peroxide. Once that’s all done, repot your plant in fresh soil. We recommend using chunkier soil as it will help with drainage, preventing root rot.
If you’re growing hydroponically, it’s a very similar process. Follow the same instructions as above for cleaning and sanitizing the roots. Cleaning the hydroponic water tank will also be almost the same, make sure to rinse it out with water first to remove any contaminated water, then sanitize with either rubbing alcohol or hydrogen peroxide. Once that’s all done, fill your tank back up with fresh water, and make sure to keep an eye on your plant to ensure the root rot doesn’t reappear.
It’s always best to simply prevent root rot, as your plant won’t go through the stress of being sick. Keeping your plant happy and healthy through its entire grow will result in larger, higher-quality harvests.
In a soil setup, you want a pot that has good drainage, so excess water can drain out the bottom. A pot with at least 5 holes is ideal. You also want to use a chunkier soil mix, so that it's less likely to get compacted and prevent oxygen from reaching the roots. Adding Perlite or Orchid bark to your soil mix would help make it chunkier. You could also purchase a higher quality soil that is already mixed to be chunky, such as FoxFarm
In a hydroponic setup, you first need to ensure there’s adequate water movement. Using an air pump and air stone is the best way to keep water moving, which adds oxygen to the water. Next, you want to ensure the water is cool enough. Warm water doesn’t allow for as much dissolved oxygen to be in the water, and harmful bacteria/ fungi thrive in warmer waters. The ideal temperature for the water in your hydroponic setup is between 69-70F (20.5-21C). For many people, if they don’t live in a warm climate their water will be around this range. If the water is over 73F (23C), this is when you may see some issues. Those living in warm climates, or trying to grow indoors in the summer may need to get a water chiller to ensure their plant is happy and healthy.
The Grobo Water Chiller is perfect for maintaining cool, consistent water temperature in a Grobo or other hydroponic environment. It’s user-friendly, runs quietly, and has high-quality 304 stainless steel rods, meaning it will last a long time and won't corrode. It even comes with a protective carrying case, so you can transport it without worrying about damaging it.
Over-fertilizing is a common problem amongst new growers. Many feel that the more nutrients you give the plant, the more it will grow, but that is not the case. If a plant receives too many nutrients, it’ll become a toxic level which would kill the plant. Think about it the same as vitamins for humans, there’s a recommended dose, and if you consume the whole bottle you may end up taking a trip to the hospital.
Generally speaking, less is more when it comes to nutrients. The plant will use what it needs, and hopefully, minimal amounts of the nutrients remain in the soil. If you’re nervous or a new grower, it may be best to use slightly under the recommended amount just to ensure you don’t give the plant too much.
To cure over-fertilization in soil, you need to rinse out the soil. You will want to heavily water the plant, and have lots of water coming out the bottom of the pot. This will ensure the excess nutrients are washed away with the water. If your plant is indoors, you could pop it into the shower for a few minutes to really flush out its soil. You could also repot the plant if you want to be extra- safe, however, that may cause extra stress. Doing a heavy flush of the soil should do the trick! Be sure to not give the plant any nutrients for at least a few weeks so it has a chance to recover.
In a hydroponic setup, you will want to fully replace the water. In a hydroponic setup, it’s much easier to get the nutrients out. Simply replace the water with fresh water, and let the plant recover before giving it more nutrients.
To prevent over-fertilization, always follow the instructions on the package. Almost every single brand of nutrients will have guidelines of how much to give your plant. Remember, you don’t need to give the plant the full amount of nutrients the bottle suggests. Give the plant a little bit, see how it reacts, and slowly increase the dose.
If you want to make feeding your plant super simple, you should go with Grobo. Grobo automatically doses the perfect amount of each nutrient to your plant its entire life. Grobo has 3000+ seed recipes, all specifically designed to fit the needs of that exact species/ strain. That way, you never need to think about nutrients, and your plant is always well-fed
Too High of Temperatures.
Cannabis plants love sun, but when it gets too warm they are unable to properly photosynthesize. Cannabis plants can generally photosynthesize and be happy in temperatures up to 82.4F (28C). Beyond that, you may notice the leaves curling, and the plant not thriving. Often the leaves will “canoe” which essentially means they take on a canoe shape, as the leaf margins curl inward.
To cure this issue, it’s the same in both soil and hydroponics. You need to get the plant into a cooler environment. If growing outdoors, move the plant into a shadier spot so it's cooler, and you can always spray the leaves with cool water when it's the hottest point of the day to keep it slightly cooler. If growing indoors, turn on your AC if you have it, or work on improving the ventilation in your grow tent if that’s what you’re using. Certain types of grow lights get very hot, and need adequate ventilation to ensure the tent doesn't overheat. Check out this blog if you would like to learn more about all the tools needed for the perfect grow tent.
Grobo offers a super cool product called Co2+. This product is designed to increase the size of yields, as it allows the plant to photosynthesize faster than normal. It’s all-natural, and simple to use. An added bonus is when a cannabis plant is exposed to higher concentrations of Co2, they’re actually able to withstand higher temperatures. To use Co2+, all you need to do is fill the bottle with water, give it a quick shake, snap the cap open, and place it in your grow area. Co2+ will last a few weeks at a time, and we carry refill sachets so you can save money and reduce your use of plastics. Win-win!
Too Cold of Temperatures
Crazy enough, if your plant is exposed to too cold of temperatures, that can also cause its leaves to curl. You want your plant to be in temperatures above (15C) below 15, your plant may get cold stressed if it’s exposed to these temperatures for extended periods.
The remedy is simple, for both soil and hydroponic setups alike. Simply move the plant out of the cold environment, or warm up the environment. This is harder to do with an outdoor grow since you can’t really warm the space. If your plant is in a pot, you can move it to a location with less wind so it’s less exposed. You could also put a tarp over your plant on cold nights to help protect it. Generally speaking, it doesn’t get too cold indoors but if it does just turn on the heat in your home or get a portable room heater.
It’s tough or impossible to grow year-round depending on your location. If you live in a climate that gets cold during the winter months, you may want to consider growing indoors. Are you unsure what kind of setup you would like indoors? Check out this blog of ours that covers the best ways to grow indoors.
At the end of the day, many growers experience curling leaves at least once in their growing career. It always helps to get educated on the topic, so you’re ready for when it happens. Luckily, you’re most likely pretty educated on the topic by now since you made it this far!
If you're looking to learn more about curling cannabis leaves, or growing cannabis in general; you should check out our cannabis growing forum AllGrowers.grobo.io AllGrowers is filled with experienced growers using Grobos, grow tents, or simply growing outdoors! It’s free to join, and we are certain you will learn a thing or two in the discussions.
Grobo just recently launched Generation 2 of the Grobo Grow Box. The new grow box is:
- More scent resistant
- Easier to clean and maintain
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So what are you waiting for? It’s time to start growing stress-free. Come learn more about the Gen 2 Grobo!