If you have reached this post because the leaves of your cannabis plants are turning yellow, let me tell you that it is quite common and that most of the time there is a solution. In our grow shop we explain the possible causes and how to solve it.

Yellow leaves on cannabis plants, why and how to fix it?

Leaves are an indicator of plant health, and the fact that leaves turn yellow is a sign that something is wrong, so let’s take a look at the possible causes of why cannabis leaves turn yellow.

Possible causes of yellowing of cannabis leaves

• Lack of nutrients
• Excess fertiliser
• Failure to regulate pH
• Crop temperature
• Over or under irrigation
• Pests or diseases

What to do when leaves turn yellow?

The first thing to do is to detect why the leaves turn yellow, a little further down you will find possible causes, but what you should NOT do in any case is to start removing yellow leaves, the leaves are responsible for absorbing the sun’s energy and photosynthesis. If you remove the yellow leaves, there will be no solution to the problem.

Lack of fertiliser

Not using the right amount of fertiliser can cause leaves to turn yellow. When cannabis plants suffer from fertiliser deficiencies, the colour of the leaves tends to become lighter and lighter green, and if these deficiencies are not covered, the leaves will eventually turn yellow.

But this can occur at various stages of the crop, one of the most common causes being a lack of nitrogen during the growth phase. When the plant suffers from a nitrogen deficiency, all the leaves start to yellow, but we will start to see it on the lower leaves of the plant (yellow lower leaves in growth, it is almost 100% likely to be a nitrogen deficiency).

How to correct a fertiliser or nitrogen deficiency

To correct this type of deficiency we must increase the doses of growth fertiliser, cannabis plants in the growth phase need high nitrogen inputs. But be careful, an excess of fertiliser can burn your plants, follow the instructions of the brand of fertiliser you use.

Excess fertiliser

Excess fertiliser can also cause some leaves to turn yellow, but this is easy to distinguish. When the plant suffers from an excess of fertiliser the leaves burn, so the leaves become bright yellow, crunchy and curl up.

How to deal with over-fertilisation

The main solution to this problem is to lower the doses of fertiliser, both in quantity per litre and in times per week. However, to avoid root blockage and to solve the problem more quickly, it is advisable to clean the roots.

Failure to regulate pH

Not regulating the pH of the irrigation water will cause your plants to not assimilate nutrients properly, when plants are not able to assimilate nutrients and we keep adding fertiliser to them, this eventually creates a blockage in the roots. When this happens, the leaves will automatically turn yellow. This error occurs more easily in coco or hydroponic systems.

Solution: To prevent this from happening, you will need to regulate the pH of the water, for this you will need to buy a pH meter. In our blog we tell you how and why to regulate the pH.

To release a root blockage, we must wash the roots, and once the roots have been washed, we must water again with fertiliser, but this time adjusting the pH of the water.

Crop temperature

Excessive temperature in the growing area can cause the plants to suffer stress and the leaves to wilt or yellow. If you grow indoors, the temperature should not exceed 26ºC, if the temperature exceeds these parameters, you should turn on the air conditioning and increase the power of the extractors.

Indoor cultivation focus burns

Be careful with the distance between the spotlight and the plants, if we do not leave an adequate space we can burn the leaves. When this happens the leaves will look burnt, yellow and brown.

Solution: To solve or prevent this from happening, leave a distance of at least 30 cm between the lamps and the tops of the plants. You can also use a thermo-hygrometer, the temperature between the light and the main crown of the plant should never exceed 26ºC in indoor growing.

Heat waves

When we grow outdoors we cannot control the temperature, but a strong heat wave can burn the leaves of our plants, this makes the leaves look yellow and dry.

Solution: In these cases it is not something that depends on us, so the only thing we can do is to cover our plants, if we grow in pots we can shelter our plants from the sun, if we grow directly in soil, we can build a structure that allows us to cover it during the days of the heat wave.

Excessive irrigation

When we water our plants we must be very careful with the amount of water we give them, as overwatering will cause all the nutrients in the substrate to be lost. This is especially true when growing in pots, as all the excess water that comes out from underneath the pots takes a large amount of nutrients with it, which will cause a nutrient deficiency.

Lack of irrigation

When we do not water our plants enough, they dry out, it is easy to see, as the leaves become limp. This is easy to see, as the leaves become limp. This can be solved quickly, we water our plants and they become well again and the leaves regain their usual shape. But be careful, every time this happens, you can be sure that more than one leaf will dry out and turn yellow.

Pests and diseases

Insect pests can cause your plants to become weaker, and many insects will even eat the leaves. This will cause some leaves to look yellow, pecked or with holes in them.

Solution: Make sure to use preventive products or insecticides to keep your crop free of insect pests.
Diseases

Cannabis plants can suffer from many diseases, and this also affects the colour of the leaves. A fungal disease like septoria will make the leaves look yellow, but with lots of little brown spots.
Solution: To solve any fungal disease, the only way is spraying fungicides, you can see the natural fungicides we have in the shop.

When should we not be concerned about yellow cannabis leaves?

Root washing: When the roots are washed during growth, it is normal for the colour of the leaves to become lighter, but when the necessary fertiliser is applied again, they will recover the correct shade.

End of flowering: Cannabis plants at the end of flowering no longer consume nitrogen, it is normal for the leaves to turn yellow at this stage of the crop. You don’t have to worry!