Do you notice how all or some of your cannabis leaves are turning yellow? The yellow leaves in cannabis may appear for several reasons, and it can be difficult to find out. But do not worry! In this article, you will learn to detect what causes this problem that we all want to avoid in our cultivation. 

Yellowing Cannabis Leaves

Many factors can cause the problem of yellow cannabis leaves from a bad pH level to nutritional deficiencies. This problem is a clear sign that something is wrong with our crop. In other words, it is how the plant warns us that something is wrong with it. To alleviate this problem, we will have to identify what is causing it. For this, we will have to carefully analyze our cultivation and observe which of the following problems may be occurring.

Don’t worry, because most cases of yellow leaves in cannabis can be cured with little effect on the final yield of your harvest. Here are some common reasons why your cannabis leaves turn yellow. 

Unbalanced pH levels 

Whether we are growing in soil, coconut or hydroponics, probably the most common reason for yellow leaves in cannabis is that the pH near the roots is too high or too low. Cannabis plants have difficulties absorbing nutrients when the pH is not correct. It results in nutritional deficiencies, even though the nutrients are present near the roots. 

The clearest symptoms of these incorrect pH levels are yellow and brown spots on the leaves and burned leaf edges. 

Growers who do not take care of the pH levels of their cultivation are often at risk of finding nutritional deficiencies in cannabis. Optimal pH levels are: 

  • Soil: 6-7 pH points. 
  • Coco/Hydro: 5.5 – 6.5 pH points. 

If we want to measure the pH levels in the water that we will use to irrigate the crop, we can use a digital pH meter. It will provide us with the necessary information in a few seconds. If we find that the levels are incorrect, we can correct them with products to lower the pH of hard water. On the other hand, if we need to raise the pH level, we must use products designed for this. 

image credit: Grow Weed Easy

Bad Watering Habits 

Overwatering is much more common, but it produces the same symptoms as underwatering. In both cases, we must learn how to provide plants with the right amount of water at the right time. 

Overwatering is more common in young plants, as their roots are weaker, and we tend to provide more water than necessary. In the same way, improperly oxygenated bad soil with poor drainage can cause the same feeling of excess water on plants.

Not paying enough attention to the plants can lead to risk problems for the crop, which often results in the loss of leaves and yellow leaves in cannabis. Some of the symptoms of poor cannabis irrigation are: 

  • Fallen plants: Although it is normal for the plants to fall slightly when the lights are turned off, we have to observe that this type of falls does not occur at the beginning of the light cycle. 
  • Leaves Swollen from Excess Watering: it especially happens if we grow a small plant in a large pot, and increasing the risk of overdoing it. 
  • Pale and thin leaves due to the lack of water inside: The chronic lack of water leads the plant to acquire yellowing of its leaves. 

On the other hand

The lack of irrigation, although more unusual, is also a problem that leads to yellow leaves in cannabis. It is difficult to detect this problem as it can be confused with nutritional deficiencies. Our main clue is that we notice that the plants come to life every time they are watered. 

To solve the problems of yellow leaves in cannabis caused by bad watering, we must: 

  • Start the cultivation with a quality substrate. 
  • Make sure the plants are in the proper size container. 
  • If the plants begin to lose firmness, immediately after being watered, you are over-watering them. 
  • If you notice how they cheer up when you water them, you are not giving them enough water. 

Nitrogen deficiency 

A lack of nitrogen often produces yellow leaves of cannabis. The main symptom is that yellow spots tend to appear on the underside of the plant. These leaves have a smooth texture and tear easily. In this way, if we observe a yellow leaf with a dry texture that is difficult to tear off, it rules out nitrogen deficiency. 

This problem usually appears when the plants have depleted the nitrogen reserves of the soil. It is something that usually happens when the cannabis has been in the same pot for too long without having been properly nourished. It is unlikely to experience this problem if we have provided the recommended amount of nutrients to our cannabis through the water. 

The good news is that it is an easy-to-solve problem: 

  • We will have to give the plants a nitrogen-based plant nutrient which will provide the plants with the correct dose of this nutrient. 
  • Transplant the cannabis to another container with fresh and oxygenated soil. 

Several other deficiencies can turn cannabis leaves yellow. Let’s look into some of the most importan ones. 

image credit: Dr. Cannabis

Phosphorus (P):

Slowed, stunted growth, possibly red leaf stems and lower leaves that turn yellow and fall off are symptoms of a phosphorus deficiency. What can you do? Simply water the cannabis plants with a fertilizer containing phosphorus. Affected leaves will not be cured. However, the cannabis plant will grow faster again, and new leaves should not show any of the above symptoms. 

Potassium (K): 

Affected hemp plants are often the best-looking and largest, but one shouldn’t be deceived. Red stems, necrotic areas (dead tissue), or pale/yellow leaves can be used to identify whether there is a potassium deficiency. Just as with the previous deficiency symptoms, a fertilizer containing potassium helps. 

Calcium (Ca):

 If there is not enough calcium in the soil, it becomes too acidic. A teaspoon of lime per liter of water helps against a too high pH value. Lime is relatively inexpensive, and you don’t have to use chemicals on top of that. 

Sulfur (S): 

A symptom of sulfur deficiency is the yellowing of small young cannabis leaves/shoots. You can combat this problem with a teaspoon of Epsom salt (sulfuric acid salt) per 4 liters of water (or a quarter of a teaspoon per liter). 

Magnesium (Mg): 

The lower cannabis leaves turn yellow, but the veins retain their green color. Leaves die and curl up. The best results are achieved by spraying an Epsom salt solution (approx. 2-3%). 

Iron (Fe):

Fresh sprouts turn yellow, but the veins on the leaves retain a lively green. Iron deficiency often occurs due to pH fluctuations. A fertilizer that contains iron can help. 

Manganese (Mn): 

Necrotic and yellowed spots appear on the top cannabis leaves. A manganese deficiency in the soil occurs due to excessive amounts of magnesium in the soil. 

Boron (B): 

Due to a lack of boron, the young sprouts of your hemp plant turn gray and die. A teaspoon of boric acid (sold as an eyewash/eye rinse) is diluted to approximately 4 liters of a boric acid solution with water. 

Molybdenum (Mo): 

A molybdenum deficiency usually causes the central cannabis leaves to turn yellow. Fertilizer containing molybdenum helps again. 

Zinc (Zn): 

The leaves get white spots at the tips and along the veins. Use zinc fertilizers or dig galvanized nails into the earth. According to some, this method works better than fertilizing with zinc.  

Not sure exactly what’s causing your plant to yellow? Use our Plant Stress Identifier to figure out why your Cannabis plant is showing signs of stress.

About the Author

Gavin D.

Gavin is a second-generation grower learning from his father before him, now stepping out into the world of LED growing and experiencing his first LED grow, also learning to grow in a hotter more humid climate after moving away from his home country over 5 years ago. Gavin is also an active member of the CLtv & 420 Growers Club community.



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