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Cannabis growers, especially beginners, are going to face pests and problems with their marijuana plants over the course of their grow. It’s just part of the deal and is something you can minimize as you get better at growing.
Luckily, cannabis plants are extremely resilient and can withstand a harsh environment or an invader for some time. This is convenient because it gives you time to figure out what the issue is and treat it before your plant is completely ruined.
Don’t freak out if something does start to happen to one of your plants, as it’s not the end! The best course of action is to view the signs and symptoms on your plant and then compare them to the symptoms listed below. Once you find the right match, continue your research and follow the instructions for how to cure it and within a few days you should see signs of recovery!
Underwatering and overwatering are the two most common problems among beginner growers and are also very easy to fix. If you are underwatering a cannabis plant, you will notice the leaves start to droop and they will seem as if they are hanging. Growth will also slow down.
If you notice these signs on your plants, all you’ll need to do is water them more frequently and give them more per watering. If your leaves are drooping, give them a quick watering and within 30 minutes they will be standing right back up nice and perky!
When you are overwatering the plant, it will cause the leaves to curl downwards and they will seem very rigid in tight because they are so full of water. Growth will also slow down tremendously and if you don’t fix it quickly, it can lead to root rot.
When overwatering occurs, it means you’ll want to water less frequently. The best method for deciding when to water is by checking how dry the soil is. If it is dry all the way around and inch deep, then it is ready to water.
If not, you still need to wait. With an overwatered plant, let it dry out for a few days and then resume a more appropriate watering schedule.
Nutrient burn is another common issue beginners and even expert growers often face, as they tend to get overzealous with feeding their plants. When it comes to nutrients, less is always more!
Nutrient burn is essentially what happens to your plants when you’ve been feeding them too strong of a nutrient mix, and/or too frequently. The edges of your leaves will begin to brown and look crispy like they were burned, and growth will slow down drastically.
The burning always starts at the very tip of the leaves, so look out for that subtle clue. If your plant begins to show signs of burn, hold off on feeding nutrients for a week or two and then you can resume. This will allow the plant to flush out the high quantity of nutes.
Whenever the tops of your plants are too close to the grow lights above, it will cause the leaves to yellow and burn. The easiest way to spot this problem is to look out for the leaves that are closest to the light; they will begin turning yellow first and then it will spread to other areas to the plant.
As soon as you spot this issue, raise your lights 6 inches to 1 foot higher. How close your lights should be is always determined by their strength and the stage the plants are in. Be sure to look at the manual your light came with as it will always explain the ideal distances for that specific light.
Growing at the wrong pH level is actually one of the most common reasons for why people experience issues with their cannabis plants. It is extremely important to mix your nutrients and waterings at the right pH as it affects how your plant absorbs those inputs.
If in the wrong pH range, it can cause your plant to go into a nutrient lockout, which means it is essentially in shock and no longer absorbing nutrients for the time being.
This is the first thing I always check for when someone is having an issue with their plants as it is almost always the answer. So before you assume you are having a nutrient deficiency, be sure you are using the proper pH levels for the growing medium you are using.
Nitrogen is one of the three main macronutrients cannabis plants survive on, so its presence is important when providing nutrients. When you look on the front of most nutrient bottles, you will see three numbers listed next to each other with dash marks. Those are the N-P-K Ratios, which are the symbols for the three main macronutrients: Nitrogen, Phosphorus, and Potassium.
When there is not enough potassium in the plants system, the leaves will begin to turn a bright yellow and will die. This is easily fixed by first checking to make sure you’re using the correct pH. If you are, then you’ll want to add a nutrient into the mix that is high in N.
Nitrogen toxicity, on the other hand, is caused by feeding too much nitrogen to your plants and is often referred to as "The Claw." This is because one of the symptoms is the ends of your leaves will curl or claw downwards. They will also turn dark green, which is another sign of N toxicity. To fix this issue, just lighten up on the amount of nitrogen mixed into the nutrient feedings.
While not as common as the previous issues, this pest is definitely one of the most damaging and difficult to deal with. If you don’t catch these guys early on, there is a good chance you won’t be able to get rid of them. That is why it is so important to always monitor your plants and to comb through them every couple of days so you can spot pests and other issues as early on as possible.
Spider mites, and most other pests, hide on the undersides of your fan leaves so always check that part of the plant as well.
It will be hard to see this best with the naked eye so I recommend using the same tool you use for looking at trichomes as that will be perfect for zooming in on them. The mites will look like similar to spiders and will be crawling around nibbling on your leaves.
The early signs of spider mites includes lots of tiny and light-colored spots on your leaves. It will look like speckles as the dots are so small and close together.
If not taken care of, you will see webs that look similar to spider webs, and they will be covering your leaves and plants. Usually at this point it is too late, but if you do catch them early on you have some options.
The best and most organic option is to use live ladybugs. You can buy them for under $10 at the gardening store and they will eat up all the mites quickly. The big issue with spider mites is they reproduce at an extremely rapid rate, so you need to make sure you kill every last one of them or they will continue to come back.
Similar to spider mites, aphids hang out on the undersides of the fan leaves, but they are green and have long legs almost like a grasshopper. They are pretty tiny as well so I also recommend using the trichome scope for looking at aphids on your leaves. You will see them crawling around and what aphids do is suck the nutrients and water out of your fan leaves, which causes them to wilt and die.
Luckily, ladybugs love eating aphids so all you have to do is add them to your plant and they will do the rest. Be sure to take care of this issue ASAP as the aphids will take out a lot of fan leaves very quickly, which will lead to smaller yields.
Also, most people recommend spraying a neem oil mix onto your plants to eliminate these bugs, but I am not a big fan of that. Reason being, if you are in flower, you don’t want to be spraying your buds with anything as it can lead to mold and rot. The other reason is the spray leaves a lasting foreign smell on the plants that is unpleasant and something I don’t want in their system.
One of the more common types of fungi you will encounter as a cannabis grower, white powdery mildew is often a result of too high a humidity in the grow room, coupled with low or no airflow. Eventually this powdery substance forms on your plants and continues to spread and make more mildew while eating up your cannabis plants.
In order to kill the mildew, it is best to mist it with a mildew eliminating spray. Also, lowering humidity and increasing airflow in the grow room is enough to stop it from coming back.
Another issue caused by high humidity and low airflow is bud rot. Overwatering can also cause this to happen, and essentially the results are the rotting of your cannabis buds. It will start from the inside and will slowly turn them brown and moldy until the whole bud is ruined.
The best way to stop the rot from spreading is by first increasing airflow and lowering the humidity in the grow room. Next, you’ll want to cut off all the buds that are infected. Mentally, it is hard to do, but if they have any amount of rot on them, the bud is useless and can make you sick if smoked.
Once you have cut off all the rot, keep a close eye on the buds for more and make sure the conditions stay where they are and you will be fine.
This is the final problem on the list and is a very important one to monitor for. Just as the name suggests, heat stress is a form of stress on your plants caused by too high of a temperature in the grow room.
The temp should be as close to 75F at all times, and once it reaches the low 80s, plant growth begins to slow down. As the temp gets hotter, the fingers of the fan leaves will begin to taco or fold up longways.
This is the easiest way to tell if your plant is experiencing heat stress and all you have to do to fix it is lower the temp to the appropriate levels.
Final Thoughts
So there you have the 10 of the most common problems cannabis growers face, as well as all the solutions to fix them before your plants are too far gone!
Also remember that with most of the nutrient deficiency and leaf problems, the issue is pH levels. So always be sure to check that first before trying to increase any particular nutrient.
Besides that, always make sure your temperature and humidity levels are correct and you aren’t tracking in any pests to the grow room. If you follow these steps, you’ll minimize most issues right off the bat.
Source: Maximum Yield,"10 Common Marijuana Leaf Problems and How to Fix Them",7/11/2019,https://www.maximumyield.com/top-10-cannabis-leaf-problems-and-how-to-fix-them/2/5054
