Updated: Dec 15, 2020
We all know that cannabis plants need to be fed nutrients throughout their life in order to survive. If you don't feed your plant enough nutrients then the plant will show signs of deficiencies. Not good. On the flip side, if you give your plant too heavy of a feeding, well, that's not good either.
The most common over-feeding problem that occurs on cannabis plants is nutrient burn (often called nute burn). What does nutrient burn look like on cannabis plants? When nutrient burn occurs on cannabis plants, the tips of the leaves on the plant will start to brown. The problem will then slowly advance up the leaf. The most notable thing about nutrient burn is that usually the rest of the leaf looks relatively healthy right up until the burn gets there. Only in late-stage nutrient burn does the whole leaf start to yellow and collapse. I usually spot it at the top of the plant first which is a indication that it is in fact nutrient burn. Potassium deficiency looks very similar to nutrient burn so growers often mistake the two. One way you can tell the difference is potassium deficiency starts at the bottom of the plant and then works its way up while nutrient burn can happen on any part of the plant.
When can nutrient burn happen? Nutrient burn can happen if you're feeding the plant nutrients or if you are growing your plant in a custom-mixed growing medium that has too much of a particular nutrient in it. You may think that the plant has a maximum amount of nutrients that it can absorb. Right? Well, that's not the case. An overabundance of nutrients in your growing medium disrupts the chemical balance in the medium. As a result of this chemical imbalance, some nutrients become unavailable for uptake while others become oversupplied. This is certainty a problem.
How do you treat nutrient burn on cannabis plants? First, flush (often called leach) your growing medium. Then, feed your plant a reduced dose of nutrients. The rule of thumb is to give the plant a 1/3 dose. While you're at it, make sure you're using nutrients that are right for cannabis. Nutrients made for tomato plants work as well. Finally, ensure you're using nutrients that are appropriate to the stage of life that your plant is in. Meaning, vegetative stage versus flowering stage.
If you follow the above steps, your nutrient burn problem should go away. The leaves that were impacted will stay burnt, but new growth shouldn't have any visible burn. Some growers are skeptical on reducing the amount of nutrients. Some say, "If I cut the nutrients then I will start seeing other problems. That's why I had to give the plant a high nutrient feeding to begin with." If you're adding so many nutrients to avoid common problems like nitrogen and magnesium deficiency then it's time to check your fundamentals.
First, what is the pH of your growing medium? Whether it's soil, water, or whatever, test it and adjust it back to where you need it. PH imbalances are often the root cause of many nutrient problems including nutrient burn. How is the temperature and humidity in your grow environment? Make sure it doesn't get too hot at midday and doesn't get too cold at night. Also, is there air movement in your grow environment? If you're growing cannabis indoors, there should be at least one exhaust fan and one oscillating fan. Finally, check to make sure that you're not over-watering or under-watering the plant. Those things can cause nutrient imbalances and problems in the growing medium as well. Knowing how to spot, treat, and prevent nutrient burn is a key piece of knowledge to have in the back of your brain so you'll be able to quickly correct the problem if it occurs.
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