K Deficiency

Potassium (K) deficiency is common on light (sandy) soils, leached substrates, or where nitrogen has been applied heavily without matching potassium. Potassium regulates water balance and nutrient translocation within the plant. The characteristic symptom is marginal leaf scorch — leaf edges turn brown and dry, with the necrosis advancing inward from the margin. Because K is a mobile nutrient, symptoms appear first on the older leaves.

Potassium is critical for maintaining the structural integrity and turgor of plant cell walls. A deficiency weakens these walls, diminishing the leaf's ability to retain water and making it highly susceptible to marginal scorching, especially under environmental stress.

When older leaves show scorched margins (as if burned) or flower buds are small and fade quickly, potassium needs to be replenished promptly:

• Pruning: Remove leaves with severe scorch — they will not recover — so the plant can direct its resources into new shoots.
• Foliar feeding: This is the fastest route to uptake. Apply a foliar spray containing potassium (KNO₃ at 0.3–0.5% or potassium sulphate K₂SO₄) directly to the leaves.
• Root drench: Drench the root zone with soluble potassium sulphate alongside the foliar spray.
• pH correction: Test the soil pH. If the soil is too acidic (pH < 5.5), potassium uptake will be impaired no matter how much you apply. Add agricultural lime or well-rotted chicken manure to bring the pH back into balance.

Recommended products

Below are three widely available and effective options:

1. Potassium sulphate (K₂SO₄) — "white potash" (fast-dissolving crystals)

• Description: Deepens flower colour, thickens petals, and improves disease resistance. Chloride-free, so it will not burn the roots.
• Dosage: Mix K₂SO₄ at the label rate — typically a small amount per large spray tank.
• Application: Spray evenly over the foliage or drench the root zone in the early morning or late afternoon.
• Frequency: Repeat at the label interval until new growth comes back healthy and green.

2. Foliar NPK with a high potassium ratio (e.g. NPK 6-30-30 or similar)

• Description: A compound foliar fertiliser used to push flowering and rapidly raise potassium levels in stressed plants.
• Dosage: Mix at the rate stated on the label.
• Application: Spray directly across the whole canopy.
• Frequency: As stated on the label.

3. Humic banana extract (an organic alternative)

• Description: Provides organic potassium naturally derived from banana, combined with humic acids that strengthen roots and improve nutrient uptake.
• Dosage: Dilute the banana extract as directed by the manufacturer.
• Application: Water directly into the root zone.
• Frequency: Apply at the recommended interval — excellent for sustained recovery.

Note: Always moisten the root zone with plain water before fertilising so the plant does not suffer fertiliser shock.

• Avoid heavy nitrogen feeding without proportional potassium.
• Test the soil regularly.