Boron is an extremely important nutrient that helps marijuana plants use calcium. It helps with maturation, pollen germination, seed production, cell division, the formulation of proteins, keeping the leaves a healthy color, and plant structure formation. It also keeps your plant’s stems, stalks, and branches at a healthy level of strength.

When there isn’t enough boron or your plant has restricted access to it, it most likely will have a boron deficiency. It is rare that a boron deficiency will be the only problem that your marijuana plant has if you do notice it has this condition. It can come from an unbalanced pH level and might come with other nutrient problems.

Boron deficiencies are most common in western soils, although even in western soils they are quite rare. A lack of boron is not mobile, which means that it will only affect new growth.

Signs of a boron deficiency

Signs of boron deficiency weed

You will start to notice your marijuana plants’ uppermost leaves growing abnormally or more slowly than usual. The tips of growths won’t grow quite right, i.e. they may appear twisted and start to die. New leaves may be wrinkled or curled.

When there’s a boron deficiency, the roots of your plants will grow unhealthily or slowly. Stems, including leaf stems and the main stem, could start to hollow and roughen. Boron deficiencies are most likely to occur when your plant hasn’t been receiving enough water, or when the humidity in the air is extremely low.

Since boron helps with your plants’ use of calcium, the symptoms can appear similar to calcium deficiencies. New growths are the parts that you will notice the biggest changes. Oftentimes a boron deficiency also comes with a lack of potassium or nitrogen, since a plant requires these nutrients in order to utilize boron.

Download my free marijuana grow guide at this link for more growing tips

When the growing tips on your marijuana plant begin looking brown or gray and eventually die, it is safe to assume that a boron deficiency is the problem. After these growing tips die, lateral shoots will start to grow, but without enough boron this growth will soon lead to death. Before they die, these shoots will appear sunburnt and gnarled, and will be a vibrant green in color.

The leaves will start developing spots on it that are brown and dead, and the surrounding tissue will clearly be dying as well. These spots are how you distinguish a lack of boron from a calcium deficiency: the spots are smaller with the boron problem.

If a boron deficiency is left untreated, it will eventually bring root growth to a halt, and will make the secondary roots shorten and swell. Because the roots are more fragile in this state, there is an added risk of fungal or bacterial infections. Unless stopped, a lack of boron will cause all the leaves on your plant to fall off, and the plant itself will eventually die.

Not sure if your plants have a boron deficiency? Read the article Nutrient deficiencies in marijuana plants for a list with pictures of all deficiencies.

How to fix a boron deficiency

How to fix boron deficiency cannabis

Most of the time a boron deficiency comes from the grower over-fertilizing their plants. Make sure to avoid this so that you don’t end up with a boron deficiency in the first place. You could use something like Marijuana Booster from the beginning to avoid a boron problem.

If you do find yourself with boron-deficient plants, you have a few options for courses of treatment. You can treat your water solution with boric acid (wiki)- one teaspoon of boric acid per gallon of water. You can use Marijuana Booster for treatment as well, as borax, compost, or compost teas.

Download my free marijuana grow guide at this link for more growing tips

Boron deficiency sometimes comes from the pH level being too high or low. In soil, roots can absorb boron the best if the pH level is between 6.0 and 6.5. In a hydroponic system, absorption of boron happens best between 5.5 and 6.2. Flush the entire system with water of the proper pH as well as nutrients mixed in. You should see new growth starting to come in normally within a few days.

A boron deficiency also might be due to a lack of potassium and nitrogen, in which case you should water your plants regularly with these nutrients. If your grow room is quite dry, you can use a humidifier to help lessen the symptoms of boron deficiency.

List of marijuana plant symptoms

Leaf Color:
– Pale leaf color
– Purple or darkened leaf color
– Dark brown spots on leaves

Leaf Symptoms:
– Browning or burnt leaf edges

Plant Symptoms:
– Thicker growth tips
– Slowed growth
– Twisted or abnormal growth

Boron is found in most tap water, so unless you are using extremely filtered or reverse osmosis water, you should not encounter a boron problem. If you are watering your plants with tap water and it appears they have a boron deficiency, first check out conditions with similar symptoms to see if boron is really the issue.

Remember that plants with strong genetics have less change of getting sick. Make sure you buy cannabis seeds from a trusted seedbank.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible


The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]


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  1. By les wilkerson ,03 Nov 2014
    I have found your articles very informative. I have printed off many. I have been growing for awhile and always wanting to learn more. I grow hydro and this article on boron is interesting I have seen this in my […]Read More
  2. By Symptom Checker – Identify Marijuana Plant Problems ,20 Jul 2015
    […] Boron deficiency […]
  3. By What Do Marijuana Plants Need? ,18 Sep 2015
    […] amounts, especially when compare to the macronutrients. Micronutrients include zinc, copper, iron, boron, manganese, and molybdenum. We’ll go into greater detail on exact nutrient requirements later […]
  4. By lilchange ,04 Oct 2017
    I just finished my first grow gave myself a c+ grade it turned out to be worse than that. On my second grow now this article as well as the rest of them has been very helpful. Thanks!!!
  5. By Anthony ,13 Apr 2018
    I have a purpleish brown color coming out on the new growth of My 3 week old marijuana plants and I was wondering if you could give Me some insight as to what it may be? They also stopped growing.
  6. By Okie2 ,05 Apr 2020
    Very helpful in learning what to look for this is my first time growing in a grow tent
    1. By Okie2 ,05 Apr 2020
      Very helpful in learning what to look for this is my first time growing in a grow tent
  7. By Reynolds ,14 Sep 2020
    So it’s one teaspoon of borax to one gallon of water

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