Boron Deficiency

Problem: New Growth is Thick Twisted or Abnormal, Brown Spots

A Boron deficiency in cannabis is relatively rare. What is known of the enigmatic role of Boron as a micro-nutrient is that it is essential for healthy and normal plant growth. Boron has a narrow margin of deficiency and toxicity in plants but the signs are easy to spot and correct.

Because the biochemical Boron is naturally derived by decomposition of organic matter in nature its total soil availability is only 5%. This is why the need for a very active soil biology is necessary or a water soluble and available source of Boron is used as a supplement. Both Boron deficiency and Boron toxicity will result in reduction of crop yield and/or impairment of crop quality.

Problem: Boron deficiency, lack of Boron availability or absorption usually seen in younger leaves/newer growth. Boron toxicity, excess of Boron absorption or availability in plants usually seen in older leaves first.


Signs of toxicity can be seen as hard to root clones and older leaves causing interveinal necrosis/chlorosis. Affected leaves are usually cupped downwards, or curled under at the tip. pH issues and reactions from other essential nutrients in the soil can also adversely cause and exacerbate a Boron toxicity.


You might have a deficiency if in new growth you see signs of abnormal and twisted growth accompanied by necrotic or chlorotic spots. A deficiency can happen when a plant is underwatered/underfeed plant or in a really dry environment. If a plant is showing signs of other nutrient/pH issues as well as abnormal and twisted new or newer growth, lack of adequate Boron might be your problem. Depending on how much of the newest growth is or continues to grow abnormally dealing with a Boron can be quick. 

Boron deficiencies may also show as a result of high calcium availability or toxicity as Calcium has an adverse effect on Boron absorption. Boron uptake has been seen to decrease with increasing Calcium concentration of the medium and because high levels of Calcium and high pH also synergistic adverse effect on Boron uptake. Care must be taken when diagnosing a deficiency as lack of Boron or availability of another nutrient in a medium issue.

A Boron deficiency can be accompanied by an apparent potassium toxicity or nitrogen deficiency, as these nutrients effect absorption. High levels of K accentuate Boron deficiency and toxicity symptoms by narrowing the tolerance range. Increasing Nitrogen and decreasing Nitrogen has been shown to control excess Boron as well as decrease the severity of Boron toxicity in some plants.

Although Boron is mobile within the soil is not readily translocated from old to young plant parts, the first symptom of Boron deficiency will be in the growing points – the stem tips, root tips, new leaves and flower buds. Boron toxicity symptoms, in contrast, typically show first on older leaf tips and edges as either a yellowing, spotting or drying of leaf tissues.

 Solution for Boron Deficiency in Cannabis

Note: Sometimes a cannabis Boron deficiency (like all deficiencies) can be triggered by stressful conditions and may clear up on its own after the period of stress is over.

Growers using unfiltered or RO water to feed their plants will rarely see a deficiency since its readily available in most tap water. Lets go over ways to reduce Boron’s deficiencies and toxicities 

  1. Use Good Sources of Nutrients

It is important to use a quality water soluble nutrient with all minor and major nutrients in proper proportions for the range you are feeding at. Higher nitrogen ppm feeds will need lower Boron levels but always watch for deficiencies. More growth means more Boron is needed to sustain that healthy growth normally associated with boosted nitrogen feeds.

Green Planet Nutrients has an unrivaled 3 part nutrient system consists of a combination of primary, secondary and micronutrients in three separate formulas: Grow, Micro and Bloom.

With a complete base food formula like GP3 you can rest assure your cannabis plants will never have Boron deficiency.

Green Planet Nutrients
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2. Adjust pH to Correct Range

Boron is best absorbed at lower pH ranges making absorption difficult in certain mediums without adjustment.

In soil, Boron is best absorbed by the roots in the 6.0 – 6.5 pH range (in soil, it’s generally recommended to keep the pH between 6.0 – 7.0, but Boron specifically tends to be best absorbed below 6.5).

In hydro, Boron is best absorbed by the roots in the 5.5 – 6.2 pH range (in hydro, it’s generally recommended to keep the pH between 5.5 – 6.5, but Boron specifically tends to be best absorbed below 6.2).

  1. Give Plants Enough Moisture

A plant in a vey low humidity and or low moisture content will show sign of Boron absorption issues. proper water practices and RH levels must be maintained for optimal growth.

  1. Watch Leaves for Recovery

Correcting a Boron deficiency or a Boron toxicity is often the same treatment. By flushing your medium with the appropriate pH solution and then charging it with balanced feed you will see new healthy growth begin to show. Watching the soil pH and feeding to run-off for a week or so should correct any imbalances.


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