Every grower knows exactly how costly cannabis leaf problems can become if you aren’t careful. Whether you cultivate outdoors, indoors, or some combination of the two, it takes time to determine exactly what works best for your plants.
From nutrient deficiencies and mildew to the constant struggle for optimal airflow and hydration, there are plenty of mistakes to be made when growing. But like most plants, cannabis does a pretty good job of showing you when something is going wrong. All you have to do is make sure you and your team know how to respond when someone spots a potential problem in the grow room.
8 Cannabis Leaf Problems to Keep an Eye on
Most hemp and cannabis leaf problems begin as a sign that can evolve into something quite destructive if left untreated. In fact, a failure to treat issues quickly will likely lower the plant’s immune system and leave it susceptible to more severe plant diseases. Fortunately, these plants are quite resilient, and if you know how to identify key cannabis leaf symptoms and resolve them quickly, you won’t have too much to worry about. We’ve highlighted some of the most common cannabis leaf problems growers come across along with the best remedies for each type.
Underwatering and Overwatering
Sometimes, excess is just as harmful as restraint, and in the case of water and your plants, that is absolutely the case. Underwatering and overwatering are two of the most common problems growers come across, especially when testing new cultivars or environments. Thankfully, your marijuana plants’ leaf surfaces are prepared to show you what’s going wrong.
In the case of a plant that’s underwatered, you’ll be able to notice drooping leaves and eventually stunted growth. If you start to notice limp and lifeless leaves, it’s time to switch up your watering schedule, allowing for more frequent watering, more water per session, or some combination of the two to perk your leaves back up so they can help fuel the growth cycle.
If your plant is being given too much water, the leaves will curl downward and appear very rigid and tight. This means it’s time to slow down the watering frequency or amount. A good rule of thumb is to wait to water until the top soil is dry while making sure there’s still some moisture about one inch deep, or roughly the length of the first thumb joint.
Nutrient burn can be quite common for newer growers, it occurs when a plant is receiving too much of any number of required nutrients. Whether you’re feeding your plant a nutrient mix that’s too strong, feeding too frequently, or both, your leaves will develop brown spots at the edge, giving a “burnt” illusion that inspired the name. Below the soil, root rot may be forming as well if the plant can’t get rid of excess nutrients.
Nutrient burn can be resolved easily by holding off on nutrient feeds for a week or two while monitoring the leaves closely until the damaged plant returns to its healthy state.
A nutrient deficiency can be just as harmful as a nutrient burn, and there are quite a few ways your plant might be affected. But whether it’s a nitrogen deficiency, calcium deficiency, potassium bicarbonate deficiency, or manganese deficiency, your leaves will show you what they’re missing.
Have your leaves started to turn yellow and curl? Boost your potassium feed. A calcium deficiency will look like small brown spots circled with dark green, stunted growth, or distorted leaves. Manganese deficient leaves will turn mottled brown and yellow, and nitrogen-deficient leaves will claw downward and turn a darker shade of green.
In severe cases of nutrient burn, your plant can suffer a “nutrient lockout,” meaning it’s entirely incapable of taking in any more nutrients. This can also occur as a result of an improper pH balance — which we’ll cover shortly — but as long as you ensure you aren’t overdoing the feeding schedule, you likely won’t have to deal with nutrient lockout.
In general, it’s a good idea to err on the side of less when it comes to nutrient mixes because a sickly cannabis plant that needs more nutrients is a much easier problem to address.
If you grow plants indoors, you’re at risk of light burn, which most often occurs when cannabis plants are placed or grow too close to the overhead light source. Overexposure to light and heat will cause your leaves to turn yellow and eventually burn. As soon as you notice this happening, raise your lights about six inches to one foot and monitor your plants closely to ensure your light source is set properly.
Improper pH Balance
Proper pH balance is vital for healthy cannabis plants — and one of the hardest things for growers to master given how frequently the pH in a public water source can change. The ideal pH for growing cannabis is 5.8 to 6.8, or just slightly toward the acidic side of neutral. Anything too far out of that range and your plants will struggle to absorb the nutrients they need to survive and thrive.
This is achieved by mixing nutrients at the right pH, which ultimately affects how your plant will absorb both inputs. Visual plant signs are a poor indicator of pH balance, which is why growers should regularly use testing strips, liquid test kits, and pH meters to ensure accurate results on a daily basis.
White powdery mildew is another common marijuana leaf problem. Indoor cultivators can expect to encounter this type of fungi with high humidity levels accompanied by a lack of adequate airflow in the grow room. You can increase airflow by removing some large and older leaves. However, if overcoming high humidity proves to be an impossible task, consider searching for mold-resistant varieties of cannabis including Blue Dream with a smaller, fluffier bud that’s less inclined to trap moisture.
You can take control of the infected plant by misting it with a mildew-eliminating spray. You can prevent it from returning by some combination of lowering your room’s humidity and increasing air circulation. If left untreated, powdery mildew will spread quickly and damage many plants along the way.
Pests are a regular problem for all kinds of plants, including cannabis. Cultivators must battle aphids feeding on plant juices, spider mites gorging on the chlorophyll of leaves, and unwanted insects that can leave “sooty mold” — a black mold produced from bugs that excrete sticky honeydew.
To resolve this issue, you’ll first need to eradicate the insect attack, using either natural options like predatory mites or harsher solutions, depending on the severity of the problem. Adult ladybugs can eat as many as 75 to 100 spider mites a day, making them a popular solution for many farms.
However, if you have sooty mold to address, one option is to use biodegradable plant-safe soap in a sprayer and wipe the sooty mold from your plant’s leaves. It will be a long and tedious process, but well worth it for the overall health of your crop.