3 Reasons why Cannabis leaves turn yellow

3 Reasons why Cannabis leaves turn yellow

Leaves that turn yellow may freak out amateur growers as it is perceived as a clear sign that something goes completely wrong. Fortunately, it is not always true, at the late stage of blooming it is simply a natural response of the plant getting ready for the harvest. Yellow leaves during the vegetative stage however may truly indicate that there are troubles. Understanding what your plant is attempting to say about its health is essential if you are aiming at getting a big and potent yield.

Once you find yellow leaves on your plant, the first action to be taken is not to start searching for the causes of it immediately but to assess whether those leaves can still be saved. If you spot that besides being yellow leaves also look droopy and weak, the best idea will be simply to remove them right away. By doing so you will help the plant to manage its energy dedicated to growth, as it won’t need to waste it on limbs that are going to die anyway.

After diagnosing which leaves shall go and which can be saved, it is important to find the root of the problem. Let’s go over the typical reasons why Cannabis leaves may turn yellow and which actions are able to fix it.


Overwatering naturally means that a plant absorbs more water than it is able to digest and release back into the air. While one of two mistakes with the water amount can’t do much harm, consistent overwatering can drastically change the environment in the grow box and cause nutrient deficiency.

Another reason might be not the actual excess of water, but the poor drainage capabilities of your growing container. Make sure that there are big enough holes at the bottom of the pot or container. There should be some water under the pot after every watering, if there is not - it is a clear sign that the soil is too rigid or the holes aren’t big enough.

Swollen and droopy leaves are the best indicators of overwatering. If you see that the leaves start drooping almost immediately after watering, call no Sherlock, this is a sure sign the plant is too saturated with water.


Overwatered Cannabis example


Solution - simply water your plant less. If all the vivid symptoms are there, the best idea is to stop giving any water until the plant starts to slightly droop. While it may seem harmful, it is actually extremely useful for Cannabis to stay on a diet for a short period. This short stress exercise will make it stronger and even increase future yields. 


In general Cannabis plants are extremely unpretentious and can do well in pretty much all summer conditions. However, strong heat at times can give

the plants too much stress and force their leaves to curl and turn yellow. That is why a responsible grower should always have a thermometer in his growing environment and constantly monitor the temperature. The ideal condition for weed is anywhere between 20 and 25 Celsius. 


Heat stress example


Solution - if you diagnosed that the temperature is too high there are 2 quick ways to adjust it. You should either increase the speed or the number of fans that generate air circulation or reduce the light intensity.


Nutrient imbalance is so far the most common cause of yellow leaves. The good news is that it is easily fixable just like the first 2 reasons. However, you would need to determine which exact nutrient is missing. It may sound complex, but don’t let it throw you off. There are clear clues that help to determine what exactly is missing.

  • Nitrogen

  • Nitrogen is the most common nutrient deficiency for yellowing leaves because it is directly responsible for chlorophyll production, which gives the leaves that healthy green color. In case of nitrogen deficiency, yellowing typically starts from the bottom of the plant and slowly creeps all the way to the top of it. Therefore, once in a while have a closer look at the bottom part of your plant

  • Potassium

  • The deficiency of potassium normally starts with curling leaves and notable brown spots, that rapidly grow until the entire leaf turns yellow

  • Magnesium

  • Magnesium is also vital for chlorophyll production. A lack of that element causes curling and blood veins on the leaf to turn yellow. Unlike with the other 2 nutrients, the consequences of the deficiency appear only 3-4 weeks after its start, which makes diagnosing it more tricky. 


    For easy diagnosing, I recommend using the memo below. It vividly represents which visual symptoms indicate the lack of particular nutrient.

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