The Leaves of My Cannabis Plants Are Turning Yellow. How Can I Fix This?

The leaves of your cannabis plants are a reliable indicator of their overall health. If the leaves start to turn yellow, it’s never a good sign. However, this doesn’t mean all is lost, as long as you can identify the cause of the problem. Most of the time, yellowing leaves are due to either too much or too little water, nutrient imbalances, improper sun exposure, or issues with the pH level of the water. It could also be related to pests or diseases.

When a plant’s leaves start to change color or shape, it’s a sign that something is wrong. Identifying the root cause is crucial for the plant to recover and continue growing without further issues. There are many factors that can cause a cannabis plant to wilt, but not all of them require the same solution. Therefore, the first step is always to determine the source of the problem.

The first rule of thumb is to stay calm and avoid rushing to remove all the yellow leaves. Remember, leaves are the plant’s way of collecting energy from the sun. If you remove them, you’ll be disrupting photosynthesis. And if the plant is young, this could easily lead to its demise.

However, if the plant is mature (i.e., in the final weeks of flowering), there’s no need to panic. It’s normal for leaves to turn yellow and eventually fall off during this stage. This is often related to the process of flushing the roots at the end of the flowering phase to remove residual nutrients, which can cause the leaves to wilt.

Yellow Marijuana Leaves: Overwatering or Underwatering?

Leaves typically turn yellow when the plant is either not getting enough water or is being overwatered. Overwatering is a common mistake among new growers. It’s easy to unintentionally flood young plants, especially when they’re in large pots. In this case, it’s best to water only a small area around the base of the plant until it starts to grow. Then, you can gradually increase the amount of water as the plant matures.

For a cannabis plant to thrive, it’s essential to provide the right watering schedule—neither too much nor too little. To check if your plant is getting the right amount of water, you can lift the pot when it’s dry and again after watering to feel the difference in weight.

If you don’t want to lift heavy pots, you can use a moisture meter to check the soil’s humidity. In hydroponic systems, you need to be even more careful. Make sure that all the equipment—programming systems, tanks, diffusers, and pumps—is set up correctly from the start. And, of course, everything should be checked regularly to ensure it’s functioning properly.

Yellow Leaves in Indoor Grows: Not Enough Light or Too Much?

It’s common to see yellow leaves at the base of fully grown plants. This is usually due to a lack of light, as the upper leaves can block sunlight from reaching the lower ones, causing them to turn yellow and eventually fall off.

This process is normal for outdoor plants, but if too many leaves are falling, you might need to move the plant to a spot where it can get more even sunlight. For indoor grows, the solution is simpler thanks to the variety of lighting technologies available. Proper lighting ensures that energy reaches all parts of the plant, improving overall productivity.

Yellow leaves and buds are more common in indoor grows due to excessive light intensity. In this case, the upper leaves and shoots are the ones that show symptoms first. As the problem progresses from the top down, you’ll need to adjust the distance of the lights to prevent them from burning the plants. Always follow the manufacturer’s guidelines to avoid this issue.

Yellow Leaves During Flowering: pH Imbalance?

Yellowing leaves can also be a sign of a nutrient imbalance or incorrect pH levels. If the pH is off, the plant won’t be able to absorb all the necessary nutrients from the water.

For soil-grown plants in traditional pots, the pH should be between 6 and 7. In hydroponic systems, the pH should be between 5.5 and 6.5. pH imbalances are more common in hydroponic setups because plants don’t have the buffer of soil, making them more sensitive to water quality.

It’s a good idea to have a pH meter on hand to regularly check the pH levels. There are also cannabis fertilizers that include pH-adjusting solutions.

Nutrient Deficiencies and Overfertilization

Cannabis plants need the right amount of nutrients depending on their growth stage. While fertilizer containers usually provide clear dosage instructions, it’s easy to overdo it or not add enough. The leaves will reflect these mistakes, and their appearance can tell you which nutrient the plant is lacking:

• If the leaf tips start to turn white, it’s a sign of zinc deficiency.
• Yellow spots on the upper leaves can indicate a manganese deficiency.
• Whitish edges and veins on the leaves are a clear sign of magnesium deficiency.
• A sulfur deficiency often causes parts of the leaves to turn reddish-orange.
• Grayish or dead shoots indicate a boron deficiency.
• If the leaves start to yellow and age, it could be due to a nitrogen deficiency.
• Round, yellow spots on young leaves may indicate a calcium deficiency.
• Curled, burnt-looking leaf edges are a sign of potassium deficiency.
• Dark, curved lower leaves suggest a serious phosphorus deficiency.

These deficiencies can be corrected with fertilizers rich in the missing nutrient. Before applying water-soluble solutions, it’s important to flush the roots. Keeping a calendar to track the feeding schedule is a good idea, and you should gradually increase the dosage to see how the plant responds. Remember, both under-fertilization and over-fertilization can harm your plants, with the latter potentially causing nutrient burn.

Yellow Leaves Caused by Pests and Diseases

Changes in leaf appearance can also be a sign of pests, fungi, or diseases. Pests are usually easy to spot, as you can often see them moving around the plant. Microorganisms or fungi, like downy mildew or powdery mildew, are more subtle. They typically form spots on the leaves that later turn into a white powder, usually on the upper surface.

The best way to prevent these issues is to properly isolate the growing area, whether indoors or outdoors. This is easier to do indoors, especially if you’re using grow tents. However, indoor grows also require strict hygiene practices. Outdoors, you need to be cautious with pets, as they can carry pests and insects.

In the end, any unusual changes in leaf color or appearance indicate an underlying problem. With the right knowledge and care, you can still achieve a successful harvest.