To say that boron is important to plants would be the height of understatement. To put it more plainly, plants simply would not exist without boron.
The reason boron is so crucial to plant health is that it is involved in ion exchange and the movement of other nutrients across cell membranes. Without boron, plants would be unable to take up phosphorus, potassium, or calcium, and would not be able to move sugars throughout the cells or regulate cellular water balance.
Boron plays a key role at the level of the roots, as well. It promotes healthy communities of the microorganisms that support proper root function. Boron ensures that plant roots are colonized with beneficial fungi and that legume roots form nodules and fix nitrogen with the aid of bacteria.
Boron is of particular importance when it comes to flowering and seed development. Besides regulating the hormones plants use to move through their life cycle, boron appears to increase the nectar production of flowers, thus attracting pollinators. Boron also ensures that pollen grains will germinate.
Most sources of organic matter contain boron. When extra supplementation is needed, many gardeners turn to the borax mined for laundry purposes.
Boron deficiency is among the most common micronutrient deficiencies found in plants across the world. It is highly susceptible to leaching, particularly in sandy soils and those with insufficient organic matter.
However, boron deficiency often results from conditions that reduce its availability and transport, of which there are many:
- High air humidity.
- Low soil temperature.
- Insufficient soil moisture.
- Severe nitrogen deficiency.
- Excess calcium.
- Weak microbe community.
Signs of boron deficiency are most common in dicots on the verge of flowering, particularly alfalfa, apples, pears, grapes, and walnuts.
Symptoms of boron deficiency appear first in new plant tissues, but may go on to affect the whole plant. They include:
- Stunted growth.
- Cracks on upper surfaces of celery stalks.
- Reddish-brown interior of celery stalks.
- Hollow stems in brassicas.
- Rough stems, stalks, and midribs on cauliflower.
- Bushy alfalfa tops.
- Death of terminal growth points.
- Pale or reddish new leaves with wrinkles and dead spots.
- Internal cabbage breakdown.
- Irregularly shaped old leaves.
- Leaf death.
- Stunted roots.
- Rough, cankered patches on beets.
- Brown or gray concentric rings inside turnips and rutabagas.
- Hollow or internally rotting beets.
- Reduced flower production.
- Brown patches on cauliflower heads.
- Failure to set fruit.
- Stunted, cracked fruits with corky areas.
- Pale, lumpy strawberries.
- Watercore in apples.
- Deformed beans.
- Incompletely pollinated corn.
- Hollow hearts in peanuts.
Once symptoms of boron deficiency appear, it is too late to prevent yield loss. However, the cause of the deficiency should be determined and addressed to prevent its recurrence.
Boron toxicity is not a problem in most parts of the world. It can occur in areas where there is an underground borax deposit in contact with water or volcanic gases. Excess boron can also build up in the soil in arid regions and in fields or gardens irrigated with contaminated water.
Plants vary widely in their susceptibility to boron toxicity. Acid-loving plants, like azaleas and peaches, tend to be adversely affected by even small amounts of boron in the soil, while cucumbers and conifers seem to be all but impervious to boron toxicity.
Symptoms of boron toxicity include:
- Stunted growth.
- Gummosis of trees.
- Pale leaf margins.
- Dead, blackened patches between leaf veins.
- Reduced fruit yields.
If boron toxicity emerges, flushing the excess from the soil with uncontaminated water is recommended. Bringing in fresh soil can also help.