How much borax should I use?

Very little — around a level teaspoon dissolved in 4–5 litres, applied once. Err low. This is not a nutrient to be generous with.

How is it different from calcium deficiency?

Both hit new growth. Boron produces brittle, corky, hollow tissue; calcium produces soft collapsing tissue such as blossom end rot.

Which crops are most affected?

Brassicas, beetroot, celery and apples are classic. Hollow or brown-hearted roots in beetroot and swede are typical signs.

Easily, and it is the main risk in treating this. Toxicity shows as scorched margins on the oldest leaves and takes far longer to resolve.

Does compost supply boron?

Generally yes, and well-composted soil rarely runs short. Deficiency is most common on sandy, heavily limed or low-organic soils.

Plant guide:🌿 Monstera 🌱 Philodendron 🌺 Anthurium 🐘 Alocasia

Back to Plant Clinic

Boron Deficiency — Deformed New Growth & Hollow Petioles — monstera plant care

⚠ Moderate

Boron deficiency disrupts meristematic cell division, producing the characteristic failure of new growth to develop normally — affected growing points abort or produce deformed, brittle tissue that tears along the midrib.

🩺

Nutrients

Boron Deficiency — Deformed New Growth & Hollow Petioles

Commonly affects: Anthurium andraeanum, Monstera deliciosa, Philodendron spp., Alocasia spp.

Emerging new leaves are stunted, thickened, or brittle — they may fail to unfurl fully, tear easily along the midrib, or develop a corky, water-soaked texture at the base. Leaf margins may be cupped or recurved. In severe cases, the growing tip aborts entirely. Boron is essential for cell wall formation, pollen viability, and the transport of sugars through phloem — its deficiency disrupts cell division in the most actively growing tissues first.

The short answer

Deformed, brittle new growth with hollow or corky stems and dying growing tips, while older leaves look fine, points to boron deficiency. Boron is immobile in the plant, so damage always shows at the newest growth — that is what separates it from the common nutrient problems. Correct it with extreme care: the gap between enough boron and toxic boron is narrower than for any other nutrient.

Confirm it before you treat it

1Look at where the damage is. Boron deficiency hits new growth and growing tips, leaving older leaves normal — the reverse of nitrogen, potassium and magnesium.
2Check the growing point. A dead or blackened tip with side shoots forced out below it is characteristic.
3Cut a stem or root vegetable across. Hollow, corky or brown internal tissue is a strong confirmation.
4Feel the new leaves. Boron-deficient tissue is thick, brittle and distorted rather than soft.
5Consider the soil. Boron leaches readily from sandy soils and becomes unavailable at high pH, so both are common backgrounds.

Potential Causes

1Boron absence in the fertiliser program — most standard NPK fertilisers do not include boron, which is required in very small (trace) quantities
2Substrate pH above 7.0 reducing boron bioavailability — boron is most available at pH 5.0–7.0
3Excessive watering or rainfall leaching boron from the substrate — it is highly mobile and easily washed out
4Very high calcium levels antagonising boron uptake — calcium-heavy hard water or calcium-rich fertilisers can competitively inhibit boron absorption

Solution Steps

1Apply a dilute borax or boric acid solution as a foliar spray: 0.2 g borax per litre of water. Use sparingly — boron toxicity occurs at relatively low concentrations and causes its own leaf damage.
2Do NOT overdose boron — the margin between deficiency and toxicity is narrow. Apply once and observe for 4 weeks before any repeat application.
3Switch to a complete micronutrient fertiliser that includes boron at a trace level (0.02–0.05% B) to provide ongoing low-level supplementation.
4Adjust substrate pH to 5.5–6.5 if it is outside this range, as boron availability declines at high pH.
5Reduce watering frequency slightly to slow boron leaching from the substrate.
6Recovery in new growth following boron correction takes 6–10 weeks — the growing tip must regenerate before normal leaf production can resume.

What else looks like this

Could be	How to tell it apart
Calcium deficiency	Also affects new growth, but produces soft collapsing tissue rather than brittle corky tissue. The two often occur together.
Herbicide damage	Twisted strap-like growth affecting several unrelated species at once, usually along one side of the garden.
Aphid or thrips damage to the growing tip	Distortion with insects present. Always check the growing point closely before diagnosing a nutrient.
Boron toxicity	Almost the opposite pattern — scorched margins on the OLDEST leaves. Caused by overcorrecting, and worth knowing before you treat.
Cold damage to new growth	Follows a specific cold event and does not recur once conditions warm.

Recovery timeline

Before treatingBe as certain as you reasonably can. Boron is toxic at concentrations barely above the useful range, and overcorrection is harder to fix than the deficiency.
Days 1–3If treating, use a very dilute borax solution — on the order of a level teaspoon per 4–5 litres, applied once. Do not repeat casually.
Week 1No change in existing damage. Deformed tissue stays deformed permanently.
Weeks 2–3New growth emerging normally is the only measure of success.
OngoingDo not reapply as routine maintenance. Address the underlying cause instead — usually high pH or organic matter that is too low to hold boron.

If you do nothing

The plant loses its growing points one after another, so it cannot extend properly and instead throws out side shoots that die in turn, producing a stunted bushy deformity. On root and stem crops the damage is internal — brown, hollow or corky centres that make the harvest inedible without any external sign. Flowering and fruit set fail because boron is directly required for pollen tube growth, so a deficient plant may flower freely and set almost nothing.

Common mistakes

Applying boron generously. This is the one nutrient where the toxic dose is close to the useful dose, and toxicity is harder to correct than deficiency.
Treating without ruling out calcium deficiency and pest damage. All three distort new growth.
Adding boron routinely as a preventative. Unnecessary applications accumulate and cause toxicity.
Ignoring soil pH. Above roughly pH 7 boron becomes unavailable regardless of how much is present — adding more does not fix availability.
Expecting damaged growth to straighten out. It cannot; only new growth reflects the correction.

Prevention Tip

Use a complete trace element supplement once per month during the growing season — these products typically contain boron, manganese, zinc, copper, and molybdenum at safe trace concentrations. This eliminates most micronutrient deficiencies, including boron, with a single product.

Questions people actually ask

How much borax should I use?: Very little — around a level teaspoon dissolved in 4–5 litres, applied once. Err low. This is not a nutrient to be generous with.
How is it different from calcium deficiency?: Both hit new growth. Boron produces brittle, corky, hollow tissue; calcium produces soft collapsing tissue such as blossom end rot.
Which crops are most affected?: Brassicas, beetroot, celery and apples are classic. Hollow or brown-hearted roots in beetroot and swede are typical signs.
Can I over-apply it?: Easily, and it is the main risk in treating this. Toxicity shows as scorched margins on the oldest leaves and takes far longer to resolve.
Does compost supply boron?: Generally yes, and well-composted soil rarely runs short. Deficiency is most common on sandy, heavily limed or low-organic soils.