Environment & care

Nutrient deficiencies

Patterned yellowing that tells you which nutrient the plant cannot get — often because of pH or roots, not because the soil is empty.

What you'd see

Nitrogen: uniform pale yellowing starting on the oldest, lowest leaves; small new leaves
Magnesium: yellow between the veins on older leaves while the veins stay green
Iron: yellow between the veins on the newest leaves, veins green
Potassium: yellow then brown scorch along the margins of older leaves
Calcium: distorted, stunted new growth and dead growing tips

Where to look

Plants in the same mix for years, plants in pure peat or coir with no feeding, and plants whose roots are damaged or whose water is very hard or very soft.

How it spreads

Not infectious.

Is it really this? Look-alikes

Root rot — Damaged roots cause deficiency symptoms with wet soil; check the roots before the fertiliser.
Natural ageing — One old leaf yellowing slowly at the bottom is normal shedding, not a deficiency.
Low light — A plant in too little light pales overall and stretches.

What's going on

Mobile nutrients (nitrogen, magnesium, potassium) can be moved by the plant from old leaves to new ones, so shortages show first at the bottom. Immobile nutrients (iron, calcium) cannot be moved, so shortages show at the top.

Very often the nutrient is present but locked: alkaline hard water raises pH and locks up iron; rotting roots cannot take up anything.

Why?

The pattern — old leaves or new, between the veins or all over — is the plant telling you which nutrient. Reading the pattern before feeding stops you adding nitrogen to a plant that needs magnesium, or feeding a plant whose real problem is its roots.

Grandmother's remedies

What people have always done — with an honest note on each.

Epsom salt drink
A teaspoon of magnesium sulfate in a litre of water, once, for interveinal yellowing on older leaves.
Verdict: Correct for magnesium deficiency specifically; useless for anything else.
Used coffee grounds
A light sprinkle worked into the surface.
Verdict: Slight nitrogen, but compacts and can grow mould. Compost them instead.
Crushed eggshells
Added to the mix for calcium.
Verdict: Breaks down far too slowly to matter in a pot. A pleasant story.
Banana peel water
Peels steeped in water.
Verdict: Trace potassium at best; more of a fungus gnat lure than a feed.

Modern remedies

What growers and extension services reach for today.

Balanced liquid feed at half strength
During active growth only.
Verdict: Fixes most general deficiencies in a few weeks.
Chelated iron
For yellow new leaves with green veins, per label.
Verdict: Effective; also check whether hard water is pushing pH up.
Repot into fresh mix
Every 1–2 years for most houseplants.
Verdict: Resets nutrients, structure and pH at once.

Honest verdict

Most 'deficiencies' in houseplants are really root or pH problems. Feeding a plant with rotting roots makes it worse. Check the soil and roots first, then read the leaf pattern, then feed.

Prevention

Repot every couple of years
Half-strength balanced feed in the growing season
Rainwater or filtered water where tap water is very hard

Plants this commonly troubles

Monstera Pothos Fiddle-leaf fig