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Boron Deficiency in Plants Causes, Symptoms, and Fixes

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Boron deficiency in plants is a common problem in agronomic, landscapes, urban gardens, or fruit trees. It often occurs with low calcium status and will result in stunted or slow unhealthy vegetative, roots, and reproductive growth in all development stages. Also, plants will have brittle distorted new growth, irregular or poor expansion of tissues, reduced turgor, meristem death, etc.

If not fixed, it will result in delayed maturation and poor quality/low yields in tubers, fruits, or seeds (poor fill). Also, they will have reduced tolerance to heat, drought, and Brix and be more vulnerable to diseases or pests.

Today, we will look at causes, symptoms, or signs, how to fix boron deficiency in plants, and how long it will take them to recover.

Boron deficiency in plants symptoms - Cabbage with hollow stems.
Boron deficiency in cabbage results in hollow stems: Image courtesy: Borax.com

How does boron help plants

Boron forms part of the cell wall membrane and promotes its integrity, aids in calcium absorption and movement, and increases sugar transport. Also, actively growing points (root tips, stem tips, buds, new expanding leaves) where cell division occurs need boron.

The other ways boron helps or benefits plants include supporting reproduction (flowering, fruiting, and seed growth), protein and RNA synthesis, and nitrogen-fixing in legumes.

Lastly, most plants need 20-100 ppm in their tissues and 0.5 – 2 ppm in soils, depending on tolerance/sensitivity. Providing excess will result in boron toxicity symptoms which will again affect your plants negatively.

When does deficiency occur?

Boron deficiency will occur when the soil has less than 0.5 ppm of hot water-extractable boron for plants requiring low boron and up to 1 ppm for those requiring higher amounts. However, exact amounts will depend on soil pH, texture, and organic matter content. 

On the other hand, Boron levels below 20 ppm in plant tissues indicate deficiency for plants that require low amounts, while those that need more are higher.

What causes boron deficiency?

There are many reasons why your plants may end up boron deficient, including the following:

  1. Low boron in tap water or fertilizers: Using fertilizers with less boron or tap water deficient in this nutrient may be a reason.
  2. High calcium level: Very high levels of calcium may reduce or inhibit normal boon uptake by plants. 
  3. Root chilling or cold root zones: Restricts boron uptake efficiency and utilization in shoots.
  4. Extreme pH: Increasing soil pH above 6.5 tends to decrease boron availability as it occurs in an undissociated form that plants cannot absorb. Also, very acidic soil, below a pH of 5.0, lowers its availability due to sorption to aluminon oxide or iron surfaces.
  5. Drought, densely packed or waterlogged soils – These soils make the roots inactive, affecting the normal absorption of boron.
  6. Too much rain or excess irrigation will leach most of the boron and other nutrients available in the soil, resulting in a deficiency.
  7. Coarse textured or sandy soil – Since they are well-drained, they tend to be deficient in boron as it leaches away. Also, these soils are bound to droughts.
  8. Overfarming: It will deplete this and other nutrients in the soil. 
  9. High humidity: When high humidity, plant transpiration or sweating will reduce, affecting absorption and movement of boron and other nutrients up to leaves and actively growing sites.
  10. Low organic matter: Boron deficiency is common in soils with less than 1.5%, especially in hot, dry (where decomposition is slow), and cold conditions. Organic matter helps hold boron. 
  11. Some minerals in the soil: Increase in lime, clay minerals (adsorb it), hydrous metal oxide iron, or aluminum oxides.
  12. Salinity: Salinity may impact boron toxicity; more studies show negative, few positive impacts.

Boron deficiency in plants symptoms and signs  

Boron deficiency in plants can go unnoticed in many plants for a long time. By the time signs show, it is severe. Usually, boron deficiency signs will first show on vegetative terminal growth points and reproductive sites, i.e., shoots (stem tips and new leaves or tissues), roots, flower buds, fruiting structures, and seeds.  

Some of the most often noted symptoms are:

  • Stunted growth, death of growth tips or terminal buds, i.e., death of meristem. Also, internodes will shorten, resulting in distorted and stubby new growth from side nodes, making the plant appear bushy or rosette.
  • New upper leaves will grow slowly and abnormally, including thickened, hardened, curled, wrinkled, or twisted leaf tips. Also, they will be susceptible to sun damage – scorch or burn – since they will have less ability to use light absorbed in photosynthesis.
  • Unhealthy and slow/stunted root growth that may be short, stubby, and have few roots hairs may occur. Also, since boron helps in sugar transport, expect reduced root colonization by mycorrhizal fungi. Why? Because the roots no longer have exudates and sugars.
  • Reduced flowering (per plant), fertility, and fruiting with distorted fruits or sometimes flowers fail to set seeds. Also, expect decreased or empty pollen production, poor pollen vitality, underdeveloped calyxes that may have brown spots, and compromised development of male and female flower parts.
  • Stems may be hollow, brittle, corky, or rough.
  • While chlorosis is not a typical symptom, the tips of lower leaves can turn yellow. Also, the younger leaves will exhibit chlorotic mottling (scattered yellowing) and, in some cases, a bronzed appearance and necrotic.

Lastly, some boron deficiency symptoms or signs may vary from plant to plant. See boron deficiency signs on various plants, including pepper, tomatoes, banana, chili, weed (cannabis or marijuana), etc.

What do boron deficiency symptoms resemble?

Boron deficiency may resemble the following:

  • Brown spots caused by calcium deficiency
  • Twisted leaves caused by tobacco mosaic virus in tobacco plants

Testing for deficiency

Signs and symptoms alone cannot confirm a deficiency. It would help if you had both soil and tissue tests. For soil, an amount less than 0.5 ppm hot water extractable boron represents a deficiency, and no less than 20 ppm for leaves. However, the actual levels to cause deficiency may vary according to plant needs.

To test for deficiency, use newly expanding leaves as older ones will not reveal true status, especially where boron is immobile.

How to fix boron deficiency in plants

Don’t wait until these signs appear. Instead, always submit plant tissue and soil sample for tests to reveal status. If results indicate deficiencies, here are some strategies to fix boron deficiencies:

a). Use boron or micronutrient fertilizers

Use premium quality boron fertilizers with foliar recommended where the soil pH is high. Alternatively, you can go for a complete micronutrient fertilizer. How much fertilizer you will use depends on what tests indicate, soil type, application method, and plant sensitivity.

Usually, plants with a high requirement will need up to 3 lb. per acre, those with moderate up to 2 lb., while those with very low 0.5 lb.

b). Amend soil pH

Since boron absorption is optimal at pH levels less than 6.2, amend soil pH to 6.0-6.5 with values of 5.5-6.5 ok. Elemental sulfur, sulfuric acid, or aluminum sulfate may help lower the soil pH.

c). Amend soil salinity

If tests show that your soil is saline, flush or leach the excess salts, and have a desalting plant. Also, capture and treat salty water and mulch crops to reduce the water needed for irrigation, among other strategies.

d). Switch from filtered to tap water

If you use reverse osmosis or filtered water, switch to tap water which has enough boron for most plants. However, don’t use well or underground water unless you test its boron level, as it may result in toxicity.

e). Minimize stressors

Stressors will only worsen deficiency symptoms. Ways to minimize them include:

  • Raising humidity to at least 25% using a humidifier
  • Properly watering your plant. Avoid drought, and don’t overwater or waterlog
  • Maintaining optimum temperature, i.e., extreme temperature (hot or cold), will only worsen things.

f). Add organic matter

Organic matter will help improve soil texture and structure, avoid quick drying, and hold on to boron. 

Frequently asked questions

1. How soon will plants recover from boron deficiency?

Plants will take days to several weeks to heal or recover from boron deficiency. i.e., for symptoms to disappear once you put corrective measures in place. However, some severely affected plants may not fully recover, while others may die.