When your cannabis plants’ leaves begin to turn yellow, it is a sure sign that something is wrong. This is one of the most common signs that your plants are under stress, so it’s important to identify and fix the problem as soon as possible.

Plants lose their chlorophyll as they age, and this causes their leaves to discolor. This can be due to a variety of issues, so it’s important to figure out what is causing the problem before taking any action.

Light Deficiency

Cannabis plants that are receiving too much or too little light can cause the leaves to turn yellow. This can be especially a problem when growing indoors, as the lights must be just right to get the best results.

If the lights are too close to the canopy, or there is no protective glass between the lamp and the plant, this can cause a type of light burn that causes your plants’ leaves to turn yellow and die. It is most common with HPS, LED or LEC lighting systems, but can also happen with older lamps that are too powerful.

Another potential cause of this is a calcium or magnesium deficiency, which can lead to the leaves turning yellow from the outside in. You can add calcium and magnesium through a Cal-Mag supplement (iron is included), but make sure you don’t overdo it.

Nutrient deficiencies are a very common reason for marijuana leaves turning yellow, and fortunately, this is one of the easiest problems to fix. The biggest symptom is yellowing leaves, but it can also be accompanied by brown spots or even curling leaves.

Over Fertilization

The leaves of your cannabis plant may turn yellow if it is over-fertilized. This can be caused by a variety of different factors, but in most cases, it will resolve itself after a few feedings.

Over-fertilization can be dangerous for cannabis plants because of the way excess salts from the fertilizer can cause reverse osmosis, which will drain moisture away from the roots and prevent them from absorbing water. This can eventually lead to chemical burns and dehydration, which will kill your plants.

If you notice your plant’s bottom leaves turning yellow, this is probably a sign of over-fertilization. Having a balanced fertilization program at target nitrogen levels during every stage of production will help to avoid this problem.

Over-fertilization can also be a symptom of other problems, like low pH levels. In this case, flushing the soil with clean water and continuing with the feeding schedule is usually all that’s needed to correct the problem.

Temperature Issues

Cannabis plants are very sensitive to temperature changes, both highs, and lows. Occasionally, these changes can be so extreme that they cause your marijuana plants to become yellow or even die prematurely.

One of the most common problems that leads to yellow leaves on your cannabis plant is over or under watering. This can be caused by a variety of factors including the substrate you are growing your plant in, or the watering schedule you are following.

The easiest way to combat this issue is to repot your cannabis plant in a substrate that retains moisture better, and to schedule watering on a consistent basis.

Another problem that can lead to yellowing leaves on your marijuana plant is excessive light, or light burns. This can happen with grow lights of all kinds, from fluorescent to more intense HID lighting. The most obvious symptom of this issue is a yellowing or browning of the buds and leaves at the top of your plant.

Pests

When your cannabis leaves turn yellow, it can be a sign of an issue that needs to be addressed. Fortunately, most problems that cause discoloration are fairly easy to fix.

First, if you’re growing in soil or hydroponics, make sure your pH is within the right range. Ideally, your plants’ roots should be at around 6.8 for soil and 5.8 for hydroponics.

Another problem that can lead to yellow leaves is nutrient deficiency. Nutrients like phosphorus can be difficult for cannabis to absorb, so older leaves will start to turn yellow.

The most common nutrient deficiency for cannabis is nitrogen, but other nutrients can also lead to yellowing. If you suspect your plants are lacking a certain nutrient, start with the lowest levels and then increase them slowly. Once your plant is back to optimal health, it should not show the signs of a nutrient deficiency again.