Why are my acer's leaves going brown and crispy at the edges?

Wind and sun scorch is almost always the answer on Japanese maples, and the position matters far more than anything you feed or spray.

Difficulty: beginner
Time: 20 min
Read: 3 min

Short answer

Crisp brown edges on a Japanese maple are scorch — from drying wind, hot afternoon sun, or the compost drying out. It is not a disease. Move the plant into a sheltered position with morning sun and afternoon shade, and keep the compost evenly moist.

Acers evolved as woodland understorey plants in a humid climate. Their leaves are thin and lose water fast, and a UK east wind in May or a west-facing patio in August is exactly what they cannot handle.

Step by step

Rule out disease first.Scorch affects the leaf margins and tips, is worst on the exposed side of the plant, and does not spread to new growth once conditions improve. Spots with yellow halos, or wilting whole branches, are different problems.
Assess the position.Acers want shelter from wind, morning sun and shade from about midday. A windy corner or an open west-facing patio will scorch even a well-watered plant.
Check the compost moisture.Acers in pots dry fast and are very unforgiving of it. Lift the pot to judge weight, and feel below the surface rather than on top.
Move the pot rather than treating the plant.For a container-grown acer this is usually the entire fix, and it takes five minutes. Against a sheltered wall, under the shade of a taller shrub, or on a north or east aspect.
Mulch the surface.A 25mm layer of bark or gravel on the compost surface cuts evaporation substantially and evens out the moisture cycle.
Water with rainwater where possible.Acers prefer slightly acid conditions and hard tap water gradually raises the pH of the compost. It is not the main cause of scorch but it contributes to a struggling plant.
Do not cut off the damaged leaves.They still photosynthesise, and a scorched plant needs the leaf area it has left. They will drop naturally in autumn.
Prune only in late autumn or midwinter.Acers bleed sap heavily if cut in spring. Any pruning is done when fully dormant, and they need very little in any case.
Check for verticillium wilt if whole branches die.Sudden wilting and death of an entire branch, with dark staining under the bark, is verticillium wilt rather than scorch. There is no cure; remove affected wood and do not replant acers in the same soil.
Repot every few years.A pot-bound acer holds far less water and scorches much more readily. Pot on one size, or root-prune and refresh the compost in late winter.

Tips

Nine times out of ten the answer is to move the pot, not to treat the plant.
Morning sun and afternoon shade, out of the wind, is the specification.
Do not cut damaged leaves off — the plant needs the leaf area it has left.

Common mistakes

Feeding a scorched acer to help it recover — Feeding drives new soft growth that scorches just as easily, on a plant that already cannot supply the leaves it has. Change the position and the watering instead.
Pruning an acer in spring — They bleed sap heavily from spring cuts, which weakens the plant. Prune only when fully dormant, and only when genuinely necessary.

If it doesn't work

Crisp brown leaf margins, worst on one side

Cause: Wind or sun scorch — Fix: Move to a sheltered position with afternoon shade, mulch and water consistently.

Whole plant crisped after a dry spell

Cause: Compost dried out — Fix: Soak the pot from below, mulch, and water more often. New growth the following year tells you whether it worked.

One whole branch wilts and dies

Cause: Verticillium wilt — Fix: Cut out affected wood well below the staining, disinfect tools, and do not replant an acer in the same soil.

Leaves scorched every spring on new growth

Cause: Cold drying east wind on soft young leaves — Fix: Shelter with a temporary screen in spring, or move the plant permanently.

Questions people ask

Is leaf scorch on an acer serious?

Not usually. It is unsightly and it costs the plant some leaf area, but a plant moved into shelter recovers and comes out clean the following spring.

Should I cut the damaged leaves off?

No. They still work, and a scorched plant needs all the leaf area it has. They will fall naturally in autumn.

Where should I put a Japanese maple?

Sheltered from wind, with morning sun and shade from midday onwards. A courtyard, a north or east-facing spot, or under the light shade of a larger tree all suit them.