Plant care guide

Indoor Citrus Sunburn: Leaf Scorch After Moving Outdoors

Updated

Why does my Indoor citrus have sunburn?

Bleached, papery or brown patches on the sunny side of an indoor citrus usually mean sunburn: leaves or bark grown indoors were suddenly exposed to full outdoor sun, or branches were opened up by pruning. Dry roots make it worse.

What to do first

Move the tree to shade or part shade, water the root ball thoroughly, and reintroduce direct sun over 10 to 14 days. Shade or whitewash bark that pruning has newly exposed.

Citrus love sun, so it is a shock when a lemon tree carried out onto the patio in spring comes back with bleached, papery leaves. The cause is usually the speed of the change, not the sun itself. Leaves that grew behind glass are not ready for full outdoor light on day one.

Your job is to stop new damage and let the next flush of leaves grow in the right conditions. Judge the tree by that new growth, not by the scorched leaves.

Confirm it is sunburn

UC IPM’s sunburn guide describes sunburned broadleaf foliage as glazed, silvery or reddish brown. The damage can progress to dead tissue starting at leaf tips, margins and between veins.

Clues that point to sunburn:

  • The damage appeared within days of moving the tree outdoors, or after a hard prune.
  • It is on the leaves facing the sun, often the south and west sides and the top of the canopy.
  • Shaded inner leaves look normal.

UC IPM notes that injury is usually worst, or only present, on the south and west sides of plants and on the upper side of unshaded branches. It also warns that water deficit and some other disorders can look similar.

Why it happens to indoor citrus

The light jump is huge. Iowa State University Extension explains in Moving Indoor Plants Outside for the Summer that even the brightest indoor location gives only a fraction of the light of a shady spot outdoors. It warns never to move houseplants from indoors straight into full sun, because leaf burn, discoloration and drop can follow.

Dry or restricted roots add to it. UC IPM links sunburn to warm weather and insufficient soil moisture. It names restricted soil volume and anything that stops roots taking up water as contributing factors. A container citrus dries out fast. Clemson HGIC notes in its container citrus factsheet that potted trees may need water almost daily in hot, dry periods.

Pruning exposes bark. UC IPM notes that older trees can be damaged when bark is newly exposed to the sun by pruning or leaf drop. Its cultural tips for citrus advise protecting branches exposed by pruning from sunburn with a 50:50 mix of white interior latex paint and water. The same page notes that underwatered citrus produce small fruit that tends to sunburn.

University of Arizona Cooperative Extension notes in its sunscald factsheet that young trees are more susceptible because of thinner bark, especially when moved from a protected nursery to a new site without gradual hardening-off.

What to do now

  1. Move the tree to shade or part shade for now. UC IPM says foliage sunburn can often be remedied by adding shade or shelter, if the leaves have not already been killed.
  2. Water the root ball thoroughly and check it daily in warm weather. Clemson advises feeling the top 5–7.5 cm (2–3 in) of mix before watering and never letting the root ball dry out completely, but not leaving it saturated either.
  3. Keep the canopy that shades the bark. UC IPM advises retaining branches that shade the trunk, so do not strip damaged leaves that still cover bark.
  4. Protect exposed bark. If pruning or leaf drop has opened up the trunk or branches, shade them or apply the diluted white interior latex paint UC IPM recommends.
  5. Wait for new growth before judging recovery.

Reintroduce full sun gradually

Iowa State’s method for houseplants is to start in full shade outdoors, then introduce more light over 10 to 14 days. Use shade cloth if no shady spot is available. Watch for burning or discoloration as you go.

Citrus differ from most houseplants in one way. Iowa State’s advice assumes tropical understory plants that should stay in shade or part shade. Citrus are sun plants. Clemson says citrus prefer full sun outdoors and need at least 8 hours of sunlight for best growth. So use the same gradual steps, but finish in full sun.

RHS gives the same advice in its citrus growing guide: introduce citrus to outdoor conditions gradually by hardening off, so they do not suffer damage or a check in growth. It also advises waiting until night temperatures are reliably warm enough before moving them out.

Avoid sunburn after pruning

  • Prune lightly. UC IPM advises avoiding summer pruning and removing no more than about 20% of the canopy in any one year.
  • UC IPM suggests pruning citrus just before bloom or just after fruit set, and avoiding late-season pruning.
  • Whitewash any bark that pruning leaves exposed to strong sun.
  • Do not combine a hard prune with a sudden move into full sun.

If your citrus dropped leaves after repotting rather than after a move outdoors, see our indoor citrus transplant shock guide.

Other indoor citrus problems we cover: honeydew residue, removing thorns from citrus tree.

References

How this guide was put together: UC IPM, Iowa State University Extension, RHS, Clemson HGIC and University of Arizona Cooperative Extension guidance.

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Knowledge record: pg-indoor-citrus--sunburn