Cannabis growers love to see lush, healthy, green leaves on their plants. Unfortunately, yellowing leaves is not an uncommon issue that growers face, and there could be a myriad of reasons why this may occur. While sometimes yellow leaves may simply be part of the growing cycle, other times they could result from a particular problem that should be dealt with promptly to ensure optimal plant growth.
Improper Water Levels
The most common reason why cannabis leaves turn yellow is inadequate watering. Perhaps there may not be enough water applied to the roots of the plant. In this case, you may notice the leaves of the plant looking thin, weak, and discolored.
On the other end, you may be watering too much. In this case, the leaves may also show signs of discoloration and swelling. If watering is identified as the problem, it’s important to make adjustments to reduce or increase the amount of water applied.
Lack of Nitrogen in Cannabis
Plant roots require the right amount of nutrients to thrive. If the plant is deficient in proper nutrients or receives nutrients in the wrong ratios, the plant will suffer. Insufficient nitrogen, in particular, may be the cause of yellowing cannabis plant leaves. [1]
Plants need nitrogen to grow, particularly when it comes to the growth of new leaves. Without adequate nitrogen levels, the leaves on the upper regions may start taking nitrogen from leaves on the lower part of the plant. In turn, the leaves will start turning yellow as they lose nitrogen. To resolve this issue, slowly increase the amount of nitrogen being fed to the plant until the leaves appear to be turning a healthy green color.
Extreme Temperatures
Plants that are grown in environments that are either too hot or too cold will not grow properly. On the one hand, excessive temperatures can stunt photosynthesis, which can lead to yellow leaves. On the other hand, low temperatures can also cause plant leaves to turn yellow and wilt.
Ideally, cannabis plants should be grown in an environment with a temperature between the range of 25°C to 30°C. [2]
Inadequate Lighting
Lighting is a key factor in the process of photosynthesis. Without adequate lighting, photosynthesis will slow down and negatively impact the growth of cannabis plants, including the yellowing of the leaves. If there is too much light, the plant leaves are at risk of burning, which can also cause the leaves to turn yellow.
The obvious solution is to place the lamps at an optimal distance from the plants. You can refer to the manufacturer’s instructions on where to hang your grow lights for optimal lighting.
Pest Infestation in Cannabis
Like any other type of vegetation, cannabis plants are vulnerable to pests. This can quickly destroy crops when not properly managed. Whether the pests involved attack the roots or the leaves, the presence of these critters can negatively impact the health of cannabis plants. It leads to weak, yellowing leaves.
Sometimes, an overly moist environment may be the culprit, particularly when fungal flies are involved. In this case, it’s helpful to reduce the amount of water and ensure the plant is not being overwatered. On the other hand, insecticides may be required to hedge against other types of pests making their way to the plant. It may also help to plant both predatory and companion species into the garden to ward off these pests.
Not all yellowing of leaves is necessarily a bad thing, particularly when plants naturally shed older leaves to save energy for new leaves and flowers. However, yellowing in other cases may be a sign of a problem. Take the time to assess various aspects of your crop to help you identify where the problem lies. Make the necessary corrections to ensure a healthy garden.
References:
1. Lu, L., et al, “Physiological and Transcriptomic Responses to Nitrogen Deficiency in Neolamarckia cadamba“, Front Plant Sci., November 2021; 12: 747121. Time Cited: 2, Journal Impact Factor: 6.627.
2. Chandra, S., Lata, H., & ElSohly, M.A., “Propagation of Cannabis for Clinical Research: An Approach Towards a Modern Herbal Medicinal Products Development“, Front Plant Sci. June 2020; 11: 958. Times Cited: 31, Journal Impact Factor: 6.627.
