Sunburn
Also known as Leaf scorch, Sunscald, Excess light damage
In short
Sunburn is damage from more light than a leaf is adapted to, usually after a plant is moved abruptly into stronger sun. The light breaks down chlorophyll, leaving bleached patches that later turn brown and brittle. It is not infectious and is prevented by gradual acclimatisation.
How it looks
Pale, bleached, whitish or washed-out patches appear on the parts of leaves facing the light, often in the middle of the leaf blade. They later dry into brown or grey-brown, papery, brittle areas. Damage is limited to the uppermost or most exposed leaves; leaves shaded underneath stay green.
Signs
Bleached or faded patches on exposed leaves; brown, crisp scorch patches; damage appearing within days of a move to a brighter spot, outdoors or to a south- or west-facing window; worse when the mix is dry.
What favours it
Moving plants from a nursery, shop or indoor spot into direct sun without transition; shade-loving plants in strong direct sun; strong sun combined with dry soil or heat.
Prevention
- Match each plant to its light needs (low, medium or high) and place it accordingly.
- When moving plants outdoors or into brighter light, acclimatise gradually: start with about two hours of direct sun a day and increase the time step by step.
- Keep the potting mix adequately moist during sunny, hot spells.
- Keep low-light plants back from south-facing windows with strong direct sun.
Treatment
Start with the first step and move down only if the problem persists.
- Move the plant to a less intense position or provide shade straight away.
- Check the mix and water if dry.
- Scorched tissue will not recover; trim badly damaged leaves once new growth appears, keeping any that are still mostly green.
- Reintroduce brighter light gradually if the plant needs it.
Pros and cons
Cons
- Damaged patches are permanent.
- Heavy scorch removes leaf area and slows growth.
Look-alikes
- Underwatering
- Drought browns tips and edges across the plant and causes wilting, not bleached patches only on the sunny side.
- Fungal leaf spot
- Fungal spots form on shaded as well as exposed leaves and often have rings or dark margins.
- Cold damage
- Chilling causes water-soaked or blackened areas after cold exposure, not bleaching after bright sun.
- Etiolation
- The opposite problem: too little light produces pale, stretched growth.
Affected plants
Shade-loving or low-to-medium-light plants placed in strong direct sun, and any plant — including herbs and vegetables — moved suddenly from lower to higher light, such as from a shop or indoors to outdoors.
Related
Sources
- Excess Light on Indoor Plants — University of Maryland Extension
- Diagnose Indoor Plant Problems — University of Maryland Extension
- How to help a poorly houseplant — RHS
- Houseplant Problems — UC Statewide IPM Program
Written in our own words from these sources. Check a product label before using any treatment.