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Boron Deficiency

Diagnosing and Treating a Boron Deficiency in a Cannabis Crop

Boron is a crucial nutrient that boosts calcium metabolism in cannabis plants. It also helps with pollen germination, weed seed production, maturation, cell division, protein formation, and leaf coloration. Boron also serves to help keep plants’ stalks, stems, and branches strong.

When boron levels are insufficient or plants don’t have ready access to it, a deficiency is said to exist. It’s quite rare for a boron deficiency to exist without the presence of other problems. Most of the time, these shortfalls come from pH imbalances and are accompanied by low levels of other nutrients.

Though boron deficiencies are more common in Western soil, they’re still quite rare. These deficiencies aren’t mobile, which means that only new growth is affected. Read on to learn more about diagnosing and treating low boron levels in cannabis plants.

The Role of Boron in Cannabis Cultivation

Like silicon and calcium, boron has a key structural role in the growth and development of marijuana plants. Up to 90% of a plant’s total boron content is found in its cell walls. Boron assists in the linking of polysaccharides (complex carbohydrates) that make up cell walls.

Among its roles, boron helps to provide the structural support and rigidity cell walls need, making plants stronger overall. Although boron has other roles, cell wall strengthening is its most important function.

Symptoms of Low Boron Levels

When cannabis plants don’t get enough boron, you may start to notice that the leaves are growing slowly and abnormally. The leaves’ tips may not grow right; they may look twisted or begin to die off. New growth may be curled or wrinkled.

In the event of a boron shortfall, a plant’s roots will grow slowly and unhealthily. Stems, including main stems and leaf stems, could begin to roughen and hollow. Boron deficiencies often occur when plants are under-watered or when there’s not enough humidity in the growing environment.

Because boron helps cannabis plants use calcium, the signs may resemble those of a calcium deficiency. You’ll notice the most changes in new growth. Often, boron deficiencies are accompanied by low levels of nitrogen and potassium, because plants need these nutrients to use boron.

When a marijuana plant’s growing tips start to die or look brown, it’s likely due to a boron deficiency. As these tips die, the lateral shoots will begin to grow, and they may look green and gnarled. However, with insufficient boron, these new growths will die as well.

The plant’s leaves will start to develop dead and brown spots, and surrounding tissues will also look sickly. These signs are how growers distinguish a boron deficiency from a lack of calcium. Spots are smaller when there’s not enough boron.

If boron deficiencies are left untreated, root growth will eventually stop, and secondary roots may become swollen. Because the plants’ roots are fragile, they’re more susceptible to bacterial or fungal infections. Unless the problem is resolved, a boron deficiency will eventually lead to plant death.

A List of Cannabis Plant Symptoms

Leaf coloration:

Pale leaves

Darkened or purple hues

Dark brown spots

Leaf symptoms:

Burnt or browned leaf edges

Plant symptoms:

Thicker growth at the tips

Stunted growth

Abnormal and twisted growth

Boron is abundant in tap water, which means you’re more likely to have problems when using reverse osmosis or filtered water. If the plants get tap water and they seem to be deficient in boron, try to rule out other conditions first.

Issues of Deficiency and Toxicity

Boron accumulates within leaf margins. Therefore, an excess will lead to discoloration and leaf death. Look for blackening or browning of the leaf tips and margins as an indication of excess boron.

In boron-mobile plants, the death of young growth and new leaves is a sign of boron toxicity. Deficiencies and toxicities will both reduce or stop growth in cannabis plants. The roots’ response to a lack of boron, especially in hydroponic gardens, can be quite sudden. Stunted root growth can happen within less than three hours when boron is taken away, and growth will stop completely within a day. This will not bode well for your crop of auto seeds or blueberry auto strain plants, but read on to find out how to treat this problem before it gets out of hand.

The situation can be quickly rectified with the addition of boron to the plants’ root zone, and improvement can be seen in as little as 12 hours. Because boron can be leached away, don’t over-water the plants. Foliar supplementation may be necessary.

Like several other important nutrients, the range between a boron deficiency and toxicity is rather narrow. At a concentration of less than 0.2 ppm, you’re likely to see symptoms of a deficiency; at 2 ppm and above, signs of toxicity may be present.

Resolving Boron Deficiencies in Cannabis Crops

Sometimes, cannabis boron deficiencies are triggered by external stressors and may clear up on their own. Here are a few ways to fix a boron deficiency.

Use reliable nutrient sources. Most growers don’t need to add boron to their plants, as tap water contains plenty of the nutrient. If you are using cannabis-specific nutrients and quality soil, boron supplementation is unnecessary. Deficiencies are more common when growers use filtered or reverse osmosis water.

Make sure the pH is within the right range. Many growers see deficiencies because boron is more readily absorbed at a lower pH. When the pH is too high, plants may exhibit symptoms of deficiency even if there’s boron in the roots. In soil gardens, boron is well absorbed when the pH is at 6.0-6.5. In hydroponic gardens, the pH should be kept at 5.5-6.2 for optimal absorption. Give the sativa or indica plants enough moisture. Boron isn’t well absorbed when there’s a lack of moisture, for example, if plants are under-watered or if the grow room’s humidity is low. Good watering methods will reduce the risk, and humidifiers can be used in dry grow rooms.

Watch for recovery. If a boron deficiency is suspected in growing cannabis plants, flush the system with clean, pH-balanced water that contains a healthy dose of cannabis-specific nutrients. Old growth may not recover if it’s already been damaged. Watch the plants over the next several days to ensure that the problem doesn’t spread.

When these steps are taken, you’ll see results within days or even hours in some cases.

The Advantages of Boron Supplementation in Cannabis Plants

Aside from its advantages for established plants, boron may also improve the health of clone cuttings. In a study using sunflower cuttings, there were positive responses. During the study, 1.1 ppm boron led to the formation of roots in non-traditional areas. Though the study didn’t form a definitive link between boron and root formation, scientists believed that the nutrient may encourage auxin production.

Additionally, because boron plays such a crucial role in the structural enhancement, foliar supplementation may diminish leaf drop-off in cuttings. Your experience may vary, and results may not be uniform in all cannabis plants.

When doing calculations, keep in mind that boron only makes up 17.7% of boric acid’s weight. Start with a low dose and gradually increase it until the boron deficiency has been resolved and the high yielding marijuana plants start to grow normally. Get the water source tested before use in hydroponic gardens, as boron levels shouldn’t exceed one part per million.

Though boron isn’t discussed as often as nitrogen, phosphorus, or potassium, it’s a crucial micronutrient that’s still being investigated to this day. Depending on the strain you’ve chosen, your plants’ need for and sensitivity to boron may vary widely. Some plants flourish with constant supplies and will respond quickly when boron is removed, while other plants are far more tolerant and have delayed responses. Check out our easy to grow weed seeds that may be the most forgiving for first-time growers.

In hydroponic cannabis gardens, it’s best to maintain an optimal boron level as the plants’ responses and subsequent declines are typically quick. The difference between boron toxicity and deficiency is quite small, so be sure not to overdo it!

Your Plants Need Boron to Survive and Thrive

Though boron is a trace nutrient, it still plays a critical role in cannabis plants’ overall health and development. It helps to maintain the balance between starches and sugars in the plants’ cells, and it moves them throughout plants as needed. Boron builds carbohydrates and sugars in the leaves after photosynthesis and it moves them down to the plant’s roots. It’s also involved in protein formation and nitrogen metabolism. Boron plays a key role in the building of cell walls and cell division. With proper boron levels, water is more effectively managed within plants. Your cannabis plants regulate the loss of water by closing and opening certain cells within the stomata in their leaves. As potassium is pushed into these cells, they open; as it’s pulled out, they close.

Boron helps plants pull water through their roots. That’s why, in many cases, signs of a boron deficiency are mistaken for those of under-watering. When you see your 3kings og or cherry pie strain plants beginning to wilt before the soil runs dry, think about having your soil mix tested to see that all the necessary micro nutrients are present in adequate levels.  With enough boron and other nutrients, your plants will grow lush, green, and healthy leaves.

The Bottom Line

Though boron is crucial to the healthy growth of cannabis plants, it’s not the only requirement. Plants with good genes are less likely to suffer from a boron deficiency. With quality seeds from a reliable seed bank like, you’ll be off to a great start.