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Salt and fertilizer burn

Also known as Fertiliser burn, Soluble salt injury, Fertilizer toxicity

DiseaseHarmful
Fertilizer burn on a cannabis leaf: scorched tips and margins Photo: Fenrisulfir · CC BY-SA 3.0

In short

Salt and fertilizer burn happens when dissolved salts from fertiliser or hard water build up in the potting mix. High salt levels make it harder for roots to take up water, killing root tips and scorching leaf tips and edges. Flushing the mix with plenty of clean water, or repotting, usually fixes it.

How it looks

Leaf tips and margins turn brown and die back, often starting on older leaves; lower leaves may drop and growth slows. Plants can wilt even when the mix is moist because root tips are damaged. A white to grey or tan crust often forms on the surface of the mix, on the pot rim or on the outside of clay pots. Roots may show dieback and decay.

Signs

Brown, scorched leaf tips and edges; white crusty deposits on the mix or pot; wilting with moist mix; lower leaf drop; stunting; in severe cases stem collapse at the crust line.

What favours it

Feeding too often or too strongly, mixing concentrate incorrectly, never watering enough to drain through the pot, pots standing in saucers of drainage water (salts wick back up), and hard or mineral-rich water.

Prevention

  • Use fertiliser at the rate and frequency on the product label; feed less when growth slows.
  • Water thoroughly so some water drains out each time, and empty saucers.
  • Leach pots periodically by running several pot-volumes of clean water through the mix.
  • Where tap water is hard, room-temperature rainwater can be used instead.

Treatment

Start with the first step and move down only if the problem persists.

  1. Scrape off any salt crust from the surface of the mix first.
  2. Leach: water with clean water, let it drain, and repeat so that a total of at least about three pot-volumes passes through the mix.
  3. For small pots or badly contaminated mix, repot into fresh mix in a clean container instead.
  4. Trim fully brown tips if desired and hold off fertilising until new growth appears.

Pros and cons

Cons

  • Burnt tips and margins do not recover.
  • Salt-damaged roots are more easily attacked by root rots.

Look-alikes

Underwatering
Drought browning comes with a light, dry pot and no white crust.
Low humidity damage
Dry air browns tips too, but without crust on the mix and without a recent feeding history.
Nutrient deficiency
Deficiency yellows leaves in patterns; salt burn browns tips and margins after heavy feeding.

Affected plants

All container plants, particularly those fed often or watered with hard water.

Sources

  1. Fertilizer Toxicity or High Soluble Salts in Indoor Plants — University of Maryland Extension
  2. Diagnose Indoor Plant Problems — University of Maryland Extension
  3. Houseplant Diseases & Disorders — Clemson HGIC
  4. Houseplant Problems — UC Statewide IPM Program
  5. How to help a poorly houseplant — RHS

Written in our own words from these sources. Check a product label before using any treatment.