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Boron For Plants: Deficiency, Toxicity, Sources, & More!

Boron is an essential micronutrient necessary for plant growth but is required in very small quantities. Boron's role in the plant is not fully understood.

Boron For Plants: Deficiency, Toxicity, Sources, & More!

Boron is an essential micro-nutrient necessary for optimal plant growth and development, but is required in very small quantities. Boron's role in the plant is not fully understood.

Boron is taken up through a plant’s root system from its growing medium, in both soil and hydroponic growing systems. It can also be absorbed through its leaves in foliar applications.

When a boron deficiency is detected, it becomes necessary to supplement with additional boron.

How Is Boron Used In Plants?

Boron is a micronutrient that is vital for good plant health. When it is not present, this can lead to severe problems with growth.

It’s unique from other nutrients in that you won’t notice any chlorosis (leaf yellowing) when there is a deficiency. However, symptoms of its toxicity are similar to those of other nutrients.

Boron is typically used, in close conjunction with calcium, for the process of cell wall synthesis. It is also needed to create new plant cells in a process known as cell division.

It is necessary for reproduction, aiding the plant with seed and fruit development, pollination, and more. Boron's list of applications doesn’t end there, though.

It's also necessary to help the plant transport carbohydrates and sugars, to metabolize nitrogen, and to form various proteins.

It can work to regulate hormones and transport potassium to the stomata of the plant.

While this last function doesn’t sound that important, it is - when a plant is unable to transport potassium, the plant might have trouble maintaining the balance of water in its cells.

This can ultimately cause it to weaken and die. Not only that, but boron is necessary for the transportation of sugars. Without boron, there will be fewer sugars and exudates in plant roots.

This can make it challenging for mycorrhizal fungi to colonize the roots - again, something that is often overlooked but incredibly important for healthy plant growth.

What Is A Good Source Of Boron For Plants?

You can treat a boron deficiency by using a complete micronutrient fertilizer, which is generally the preferred method of treating a deficiency.

That’s because soil and growing solutions that are deficient in boron are usually also lacking in other micronutrients as well.

However, you can also use a boron supplement. You will need to be extremely careful when doing this, though, as it’s easy to overapply a boron supplement.

Some options include boric acid and borax. Most people use a small amount (½ teaspoon per gallon of water) of boric acid as a foliar spray. Just be careful, as too much boron can also be problematic.

There are certain plants that are more prone to boron deficiency than others, too, including salvias, petunias, impatiens, and pansies.

You may want to avoid these plants if boron deficiency is a consistent problem for you.

There are other plants that aren’t necessarily prone to deficiencies, but are heavy boron users.

If you grow crops like cabbages, pears, grapes, apples, Brussels sprouts, broccoli, cauliflower, and turnips, you may want to use a light boron spray as an annual prophylactic measure.

Boron Deficiency

Boron deficiencies are very rare and are often accompanied by calcium deficiency. They occur most often when plants are under-watered.

Potassium and phosphorus nutrition is enhanced by boron. Boron plays a significant role in maintaining proper functioning and strength of plant cell walls.

It also has a positive impact on root uptake of potassium and phosphorus, two vital macro-nutrients for our plants.

Boron deficiency will still allow the plant to grow to a reasonable size, but in a weaker state. You will experience death at growing points, and flowers and buds will fail to develop.

Here are some additional symptoms you can watch for to help you identify a boron deficiency in plants.

Identifying Boron Deficiency In Plants

Leaf symptoms of boron deficiency will appear in the upper, young leaves. Slight yellowing may occur, and the tips of leaves will turn brown to black and die off.

The stems may also be affected by becoming brittle, displaying cracks along the surface of the stem, or becoming hollow.

  • Young leaves will experience tip burn
  • Young leaves will curl and wrinkle
  • Growing tips die
  • Root tips will swell and stop growing

Examples Of Boron Deficiency On Leaves

Boron nutrient deficiency for plants

Crop Specific Symptoms Of Boron Deficiency

  • Apples—interacting with calcium, may display as "water core", internal areas appearing frozen
  • Beetroot—rough, cankered patches on roots, internal brown rot.
  • Cabbage—distorted leaves, hollow areas in stems.
  • Cauliflower—poor development of curds, and brown patches. Stems, leafstalks and midribs roughened.
  • Celery—leaf stalks develop cracks on the upper surface, inner tissue is reddish brown.
  • Celeriac—causes brown heart rot
  • Pears—new shoots die back in spring, fruits develop hard brown flecks in the skin.
  • Strawberries—Stunted growth, foliage small, yellow and puckered at tips. Fruits are small and pale.
  • Rutabagas / Turnips—brown or gray concentric rings develop inside the roots.
  • Palm Trees—brown spots on fronds & lower productivity.

How To Correct Boron Deficiency

One of the first things to take a look at is pH balance, in both soil and hydroponic growing systems. A pH imbalance will block nutrient uptake through the plant’s roots.

It is important to regularly check the pH and to be sure to keep the pH within the appropriate range for soil or hydroponics. The optimal pH range for most plants is between 5.5 and 6.5.

In this range, the nutrients present in the soil or water are soluble and are easily taken up through the plant’s root system.

When the pH level is outside of this range, even when appropriate levels of micro and macronutrients are present, they are not able to reach the plant.

Alternative methods for correcting boron deficiencies

Another great approach to correcting a boron deficiency is through supplementation. A nutrient supplement that contains kelp will give plants a much need boost of boron, along with the added benefit of calcium and magnesium.

Another method a lot of gardeners and growers like to apply is with the use of borax or boric acid. This simple supplementation method can be used in soils, soilless growing, hydroponic systems, and as a foliar spray.

Caution: The leaves of many types of plants are damaged by the application of boron so it is best to apply it to the soil or hydroponic solution.

Household borax should be applied at a rate of ½ tsp. of borax with 1 gallon water. If you suspect a boron deficiency problem with your plants, a dose of borax will do the job.

Boron can quickly become toxic if applied in excess. Keep concentrations below 20 ppm under normal growing conditions for optimal results. Boron is sometimes a component of insecticide so it is best to avoid excessive amounts of boric acid-based products.

Now that you know the benefits of monitoring the boron content in your soil and hydroponic growing systems, and what to do when you spot a deficiency, you can be sure to have the necessary tools on hand to keep your plants at their best.

Boron Toxicity In Plants

The signs of boron toxicity are quite similar to those of other nutrients. Sometimes a few older leaves of the plant will begin to show a slight tip chlorosis, but this is more common with other nutritional deficiencies than it is with boron.

Boron toxicity often sets in quickly, leading to the full death of a leaf and complete defoliation of the plant. It will rapidly affect lower leaves, too. Toxicity is much more common during dry seasons or when you apply too much compost to the soil.

It is difficult to avoid the toxicity of boron when you are treating a deficiency, because the line between “too much” and “too little” is incredibly thin. It is often easier to prevent toxicity by monitoring the growing medium’s pH (as well as the pH of your water) and nutrient levels.

Boron toxicity is more likely to concur if the growing medium has a pH lower than 5.5-6.0 or if there is has been too much boron applied with fertilizer.

It isn’t likely to occur on its own or due to natural causes. If you find that your plants are suffering from a boron toxicity (b sure to conduct a thorough soil test to make sure this is the culprit and not something else), you should leach the solution to flush and rinse out any extra boron.

Then, apply a fertilizer containing calcium, as calcium will render boron unusable by your plants.When irrigating your plants, test the water first.

Many irrigation water sources contain plenty of boron (0.3 to 0.5 ppm) so you don’t need to supply extra boron with a fertilizer.

If you need to fertilize for other nutrient deficiencies, use a boron-free fertilizer to prevent toxicity.

Final Thoughts On Boron For Plants

If you just grab a complete nutrient package, and follow your feeding chart properly, you likely won't ever have to deal with a boron deficiency.

This is a vital nutrient, despite the fact that it's not as prominent as some other micronutrients you hear of in gardening.

Nevertheless, your plants need boron - so make sure to feed properly, and watch for symptoms of deficiency or toxicity! Read our entire nutrient deficiency series as well to learn about other vital plant nutrients.

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