Cannabis: Yellow leaves

Yellow leaves on cannabis plants are a common problem that can be due to a number of causes. They are often a sign that something is wrong with the plant and can range from nutrient deficiencies to environmental influences. Here you can find out the main causes and what solutions are available to get your plant back on track.

The pH value of the soil is decisive for how well the plant can absorb nutrients. If the pH value is outside the optimum range (between 6.0 and 7.0), nutrient blockages can occur. In this case, the nutrients are present but the plant cannot absorb them, which can also lead to yellow leaves.

Solution: Check the pH value of the soil regularly. If this is not in the optimum range, you can adjust the pH value with appropriate products to ensure that the plant can absorb the nutrients.

Cannabis plants need plenty of light to grow healthily. A lack of light can cause the leaves to turn yellow, as the plant cannot produce enough energy through photosynthesis. Other environmental influences such as extreme temperatures or excessive humidity can also lead to stress, which manifests itself in yellow leaves.

Solution: Make sure your plants get enough light, especially during the flowering phase. Also pay attention to the temperature and humidity levels in your grow room to ensure optimal growing conditions.

Removing yellow leaves from cannabis plants is not always necessary immediately. It depends on how badly the leaves are damaged and what stage your plant is in. Yellow leaves can stress the plant and reduce the energy it needs to produce flowers. But there are a few things to consider before you reach for the shears.

When should you remove yellow leaves?

If the leaves are completely yellow and no longer have any green areas, they have lost their function and no longer contribute to the plant's energy production. In this case, it makes sense to remove them to relieve the plant and improve the air flow between the leaves, which can prevent mold and fungal infestation.

Solution: Carefully cut off yellow leaves with clean scissors or a knife so that the plant can concentrate on the healthy parts.

When should yellow leaves not be removed?

However, slightly yellow or partially yellowed leaves may still contain nutrients that the plant can use. Especially during the growth phase, it is advisable to leave the leaves on the plant for the time being while there is still some green. They can still contribute to photosynthesis and provide the plant with energy.

Yellow leaves in the flowering phase

In the flowering phase, it is normal for some older leaves to turn yellow as the plant concentrates its energy on flower formation. In this phase, you can regularly remove yellow leaves to focus on flower production and keep the plant healthy.

If cannabis develops yellow leaves shortly before harvest, this is often a completely natural process and no cause for concern. In the final phase of growth, the plant concentrates its energy on the flowers, which means that it transports fewer nutrients to the leaves. This causes the leaves to turn yellow, especially the older, lower leaves.

Why do the leaves turn yellow?

During the last weeks before harvest, the plant stops receiving most of its nutrients. It begins to use the nutrients stored in the leaves to feed the flowers. This process of nutrient displacement causes the leaves to lose their green color and turn yellow. It is a sign that the plant has reached its ripening phase and the harvest is near.

Do you need to do anything?

In most cases, you don't need to intervene if your cannabis plant turns yellow just before harvest. It is a natural part of the ripening process. However, removing the yellow leaves can improve airflow around the flowers and prevent mold, especially if you are growing in a humid environment.

Cause: Potassium deficiency

A common reason for brown spots on yellow leaves is a lack of potassium. Potassium is an important nutrient that is responsible for regulating the plant's water balance and nutrient uptake. A potassium deficiency often causes the leaf edges to turn yellow and brown, dry spots to form.

Solution: Use a fertilizer with a high potassium content to compensate for the deficiency. Also make sure that the pH value of the soil is in the optimum range (6.0-7.0 for soil) so that the plant can absorb the potassium.

Cause: pH problems

Sometimes the required nutrients are present in the soil, but the plant cannot absorb them due to an incorrect pH value. Soil that is too acidic or alkaline blocks the absorption of potassium and other nutrients, resulting in yellow leaves with brown spots.

Solution: Check the pH of your soil and make sure it is in the optimal range. If necessary, you can adjust the pH value to improve nutrient uptake.

Cause: Over-fertilization

Another possible problem is over-fertilization. Too much fertilizer can damage the roots and lead to salt accumulation, which in turn hinders nutrient uptake. This can cause yellow leaves and burnt brown spots.

Solution: Rinse your plants with clear water to remove excess salts from the soil. Reduce the amount of fertilizer and only use as much as the plant actually needs.

Pests as the cause

Spider mites or other pests can also leave brown spots on the leaves. These small insects suck the plant sap from the leaves and leave behind yellow to brown spots that become larger over time.

Solution: Check your plant thoroughly for pests. In case of infestation, you should take immediate action, e.g. by using biological pesticides or natural enemies such as ladybugs.