boron deficiency marijuana

Boron Deficiency In Cannabis Plants

Modern cannabis nutrients perform very well for pretty much everyone. If things do go wrong and your marijuana looks sick, it could be a boron deficiency. Find out the basics about deficiencies in the cannabis plant from the pros at RQS.


Boron is an essential micronutrient in all plants. It supplies structural integrity for cell walls, helps maintain the plasma membrane and promotes the health of other metabolic pathways. Insoluble boron plays a major role in plant integrity. Soluble boron is more likely the culprit for overdoses; however, soluble boron is the source for insoluble boron used in plant cells.

Boron is fixed once it is taken up by the plant, so a boron deficiency only occurs in new growth. Nitrogen, calcium and other essential plant nutrients work in concert with boron to ensure plant health. Plants may display a number of deficiency symptoms if there is a lack of boron. For example, grey or brown dry spots may occur that look similar to signs of a calcium deficiency, only the spots are larger. Similarly, purple stems can be a symptom of cold, nitrogen toxicity or boron deficiency. Only with boron, stems become much more soft.

A boron deficiency can drastically affect the quality of your plants. The follow may result from such an occurrence:

  • Inhibits turgor. Plants will lose their lushness. This is easily observed in marijuana as the plant is universally admired for vibrant growth.
  • Reduces fertility. Less pollen is produced, which also encourages sterility. Calyxes become underdeveloped and bracts, which are modified leaves, will show symptoms such as small, dead, brown spots.
  • Affects vegetative and reproductive growth. Overall growth at all stages can be affected. Vegetation is stunted and growth is slowed. Flower development, both male and female, is severely compromised.
  • Can kill the meristems. These are plant tissues which contain undifferentiated cells that are essential for plant growth.


Boron deficiencies usually occur when a plant is underwatered or subjected to low humidity. Boron deficiencies can mimic calcium deficiencies as both elements rely on each other to maintain overall plant health.

The following are symptoms of boron deficiencies:

  • New vegetative growth that is twisted and burnt unfolds and expands more slowly. New growth eventually dies and falls off, effectively topping the plant. New side shoots lack vigour, curl and turn grey or brown.
  • New growth is thick and the tips seem clustered, rather than expanding and growing taller. The primary tip leaf cluster may be vivid green.
  • Sugar leaves will no longer “reach for the light.” Because boron is essential for cell strength, the whole plant will eventually droop and collapse instead of fall over.
  • Leaf stems and branches appear soft and lacklustre and may even turn purple. Essential metabolic functions are interrupted with a boron deficiency and the whole plant suffers.
  • Slowed root growth. Eventually, main roots will die off and secondary roots will be stunted and swollen. This makes them prone to bacterial infections and rot.
  • Small brown spots surrounded by dried tissue expand across the whole leaf. Eventually, the leaf will crumble away.
  • Main stalks and branches appear rough and brittle and can become hollow.


To help prevent a boron deficiency:

  • Make sure plants do not dry out too often.
  • Don’t over-fertilise! This will cause nutrient lockout.
  • Make sure the humidity is above 25%. A humidifier or dehumidifier is always a good idea when growing indoors.
  • Always use cannabis-specific nutrients with the necessary cross-section of elements.
  • Soil growers should use a comprehensive, well drained soil.


In the unlikely event of a boron deficiency:

  • Apply a mix of 1 teaspoon boric acid to 4 litres of water to the affected plants. Results will be noticeable overnight.
  • When plants show positive reactions, flush with clean water or a commercial marijuana tonic and begin normal nutrient routine.

Boron is found in most tap water, so those growers using very filtered or RO water are most at risk. With all deficiencies, make sure you have tested the basics first. That means water quality. Test the pH. Depending on how you measure dissolved solids, check the EC or ppm. These two primary water conditions can imitate many deficiencies in the cannabis plant. Once you are satisfied with your water, it is time to start hunting for the real culprits.

Although rare, a boron deficiency can severely compromise your marijuana plants. This is how to identify and treat a boron deficiency in cannabis.

How To Know If Your Cannabis Plants Are Suffering From A Boron Deficiency

Published : Aug 29, 2017
Categories : Cannabis cultivation

A boron deficiency has the possibility to harm or reduce your harvest. Since every grower wants to have the biggest yield their plants can possibly produce, spotting deficiencies early can make a huge difference.

Plants use boron to transport sugars, metabolise nitrogen and form proteins. But most importantly, it is used with calcium to create new plant cells and generate healthy new growth. Especially with flowering cannabis, plants have a greater need for boron because it is also used in fruit and seed development, and for pollination.

Boron deficiencies appear mostly in cannabis plants that have not been watered adequately or that are growing in a very arid environment with very low humidity.

A boron deficiency is a relatively rare occasion, but it can lead to stunted growth in leaves as well as the root system. If left untreated, it can really hurt your final harvest.

Even though the signs may be quite apparent, it is very easy to confuse a boron deficiency with a calcium deficiency, as plants need boron to properly use calcium at all. Very often, a deficiency of boron is combined with a deficiency of nitrogen or potassium, as plants in turn need potassium and nitrogen to properly process boron (to then process the calcium).


The first visible signs of a boron deficiency will likely be slowed or abnormal growth in the upper leaves of your cannabis plants. The tips of new leaves may display twisted growth, wrinkle, curl, or even die off. The abnormal growth is usually accompanied by yellowing of the leaves and the appearance of brown spots.

A boron deficiency does not only affect the growth of new leaves, it also affects the plant’s root system, albeit with less visible symptoms. A deficiency can stunt the growth of new roots or cause abnormal growth with hairs on the roots. Stems of the plant can also be affected, becoming hollow or weak.


The first thing to pay attention to when battling a boron deficiency is to make sure that you are using the right nutrients. This is easier than you might imagine since most tap water contains boron by default. You would have to use something special, such as water that has been filtered with a reversed osmosis filter, to deprive your plants of boron. Most high-quality soils also contain high enough levels of boron for your cannabis plants to never experience a boron deficiency.


Moving on from the nutrients, we arrive at the issue of the pH levels and growing mediums. If the pH levels are not right, the roots cannot absorb the nutrients they need and thus, a deficiency can occur. Concerning deficiencies, boron seems to be most efficiently absorbed by plant roots at pH levels between 6.0 and 6.5. Even though most growers keep their cannabis plants at pH levels between 6.0 and 7.0, boron seems to be best absorbed below 6.5. In hydro cultures, growers keep their plants at pH levels between 5.5 and 6.5, but at pH levels below 6.2, the plants roots most efficiently absorb boron.

When your plants have the nutrients they need and the correct pH levels to absorb them, there is only the issue of under-watering that is left. Watering the plants more regularly (but not too much) should be an adequate solution. However, if humidity levels stay too low, you could add an air humidifier. The levels should not drop below 25% humidity in your growing space.


When all the above conditions are met, your plant should be able to recover within a few days to weeks, depending on how serious the damage from the boron deficiency was. The growth that is already abnormal will not recover, but new growth should appear regular again and without abnormalities. If the problem persists, you can always flush your cannabis plants with pH-balanced water and the correct nutrients.

Even though we describe the conditions in which a boron deficiency might occur, a deficiency can also be caused by temporary but stressful conditions and may disappear when the plant’s growing conditions return to normal.

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Click here to find out how you can spot an early boron deficiency in your cannabis plants and how to solve it before it hurts your harvest.