Chlorosis is a common problem for general gardeners and cannabis growers alike. Chlorosis refers to a lack of chlorophyll. This deficiency results in leaves turning from green to yellow. The good news is that this problem is easy to solve once you can diagnose the cause of your cannabis leaves turning yellow.
Some of the most common causes of yellow cannabis leaves are:
We unpack each of these common causes to help you diagnose the problem with your cannabis plant. To accurately diagnose the cause of your cannabis leaves turning yellow, you must understand each possible scenario.
Yellow marijuana leaves can signal a lack of nutrients in cannabis plants, but most cases point to underfeeding. Nutrient lockout must always be considered when your cannabis leaves turn yellow. Nutrient lockout happens when the environmental conditions prevent the plant’s roots from absorbing minerals from the soil or other growing medium.
Nutrient lockout commonly occurs when the soil pH falls outside of the ideal range. The list below outlines the optimum pH range.
Recommended pH Levels for Growing Cannabis:
- Soil – pH of 6.0 – 7.0
- Hydroponic – pH 5.5 – 6.5
Big changes in acidity reduce the availability of nutrients such as nitrogen. It is important to manage the pH first before adding more feed, otherwise, the plants will not develop as they should, and the plant feed will have no effect regardless of how much you add.
To maintain optimum pH levels use a pH meter to measure the pH and use a bottle of either a pH Up or pH Down solution to balance the pH level according to the type of growing medium.
Yellow leaves may also point toward nutrient deficiency. Nitrogen deficiency is a common reason for yellow cannabis leaves. A lack of nitrogen in the soil can cause cannabis leaves to turn yellow around the edges with chlorosis eventually spreading to the middle stem.
Brown spots indicate either a potassium or calcium deficiency, and iron or magnesium deficiencies will also cause cannabis leaves to turn yellow.
Don’t forget it is crucial to feed your crop with the correct quantities of nutrients too. Be careful of overdoing it with nutrients because using too much can also cause nutrient burn.
Some cannabis strains are known to change colour when grown in colder temperatures during the flowering stage, however, growers need to use strict temperature control systems to keep the environment well balanced. Temperatures colder than 10 ºC or warmer than 28 ºC can cause green leaves to turn yellow.
When growing indoors you will need to have some control over the room temperature and outdoor growers will need to make their plants more comfortable with some extra TLC for the THC. Greenhouses are recommended to protect your plants from both warm and cold temperatures and will help to avoid stunted growth.
Firstly, watering too much can sometimes cause cannabis leaves to turn yellow. This essentially suffocates the cannabis plant’s roots causing less oxygen to be absorbed.
Secondly, always use filtered water to maintain a good pH balance. Remember, Nutrient Lockout occurs when there is a pH imbalances in the soil which also leads to cannabis leaves turning yellow.
Overwatering may also present other issues like root rot, especially if your cannabis plant doesn’t have good drainage. Waterlogged soil can fast become a breading pool for fungi and bacteria. When fungi and bacteria are present they attack the cannabis plant’s root system. With root rot setting in the cannabis plant will show unhealthy characteristics like droopines and yellow cannabis leaves.
To prevent root rot of your cannabis plant ensure your soil or growing medium has good drainage and air circulation.
There are many pests that are drawn to the cannabis plant but when it comes to cannabis leaves turning yellow these are the pests you need to be aware of.
Spider mites feast on cannabis leaves and are extremely damaging to the overall plant and harvest. Spider mites tend to cause the remaining cannabis leaves to turn yellow and also nest in the bud foliage. They can be killed with aromatic oils like cinnamon oil but if the damage is too severe, particularly where nesting occurs, then your only option is to prune the affected foliage.
Fungus gnats can also cause cannabis leaves to turn yellow and are common pest that like to hatch their larvae in wet soil. To eliminate fungus gnats hold off on watering for a few days until the soil dries out. This will prevent the larvae from hatching and the fungus gnats will move to find a better host.
Lighting is more specific to grow room environments, so it is crucial to get the setup right to avoid cannabis leaves turning yellow. When using a grow room or tent, keep grow lights at a reasonable height above the cannabis plant. Find the Goldilocks zone that is just right.
Hang lights too low will cause heat stress and burn the tops of your cannabis plants. This causes the upper leaves of your cannabis plant to turn yellow or brown. However, hanging lights too high may not deliver enough photons to the lower cannabis leaves. Without enough light your cannabis plant will start to look flat and droop.
Don’t Ignore Cannabis Chlorosis
Chlorosis is a clear indication of an underlying issue with your plants. Look at your growing environmental and its conditions to help you accurately diagnose the problem. Keep it clean and keep it green, good luck.