Outdoor plants in a Dubai garden take leaf temperatures well above the 45C air around them in July and August. This guide explains what heat stress and sunburn are, shows the scorch pattern that tells sunburn apart from water stress, covers which plants burn and when, and sets out how to shade them without cutting the light they need.
What heat stress and sunburn are
Heat stress is the slowdown a plant goes through when leaf tissue runs too hot to work normally. Sunburn is the physical damage that follows when direct sun overwhelms a leaf's defences, bleaching and killing a patch of cells. Heat stress reverses in the evening. Sunburn does not.
A leaf in full sun can run up to 10C hotter than the air once its pores close. Water leaving through those pores is what cools it. When the air is 45C and the soil is dry, that cooling fails, and the leaf surface can pass the 50C mark at which cell proteins start to break down.
Heat stress shows as leaves that fold, roll or hang limp through the afternoon, then recover by sunset. The plant has closed its pores to save water. Repeated day after day, it stops growing but carries no permanent mark.
The scorch pattern that tells sunburn from water stress
Sunburn and water stress both leave brown, dead leaf tissue at 45C, but in different places. Sunburn marks the centre of the leaf blade on the sun facing side of the plant. Water stress starts at the leaf edges and tips, across the whole plant.
Three readings separate them:
- Where on the leaf the damage sits, centre of the blade for sunburn and edges or tips for water stress.
- Which side of the plant carries it, the south and west faces for sunburn and every side for water stress.
- Whether shaded inner leaves are affected, never for sunburn and yes for water stress.
- What the damaged patch looks like, bleached white to pale tan with a sharp edge for sunburn, and brown with a yellow margin that spreads inward for water stress.
Sunburned leaves stay firm, because the plant has water. It was the light that did the damage. Water stressed leaves feel soft or papery and the plant wilts through the heat of the day.
The quickest check is a leaf on the shaded north side of the canopy. If it's clean, the problem is light. If it carries the same brown edge as the sunny side, the problem is water, and the irrigation needs checking before any shading goes up.
Which plants burn and when
Plants burn in the UAE when they meet more sun than they were grown under. The highest risk comes in the first 3 weeks after planting a nursery raised plant into full sun, and in the first days of May when the sun angle climbs.
Nursery stock is raised under shade netting. A gardenia or a citrus tree moved from netting straight into an open bed in June burns inside a week, even with ample water. The leaves grown in shade are thinner and carry less protective pigment than leaves grown in full sun.
Bark burns too. Young citrus, mango and frangipani trunks crack and peel on the south west side where afternoon sun strikes bare bark, which is why growers here paint young trunks with diluted white water based paint.
Potted plants moved outdoors for winter and left out into May face the same risk. A terracotta pot on a south facing terrace absorbs heat through its wall, so the roots cook while the leaves burn, and the plant shows both patterns at once.
How to shade plants from summer sun
Shade plants by cutting the harshest afternoon sun rather than all light. A 30 to 40 percent shade cloth over sun loving shrubs from May to September, or a structure that blocks the sun after 1pm, stops burn while leaving enough light for growth.
For a newly planted shrub, step the exposure up over 2 weeks. Start with morning sun only, then add an hour each few days. Leaves grown during those weeks are thicker and burn less.
For a permanent answer on a west or south facing bed, fixed shade does more than seasonal cloth, and shade structures and pergolas built over a terrace or planting bed take the afternoon sun off the plants below every summer, with no cloth to fit and remove each year.
FAQ
Scorched gardens produce a short list of questions after the first heatwave in May. The three below cover what the damage looks like up close, what happens to burned leaves, and which plants hold up to full UAE sun.
What does sun scorch look like on leaves?
Sun scorch looks like a bleached, white to pale tan patch in the middle of the leaf, with a sharp edge between dead and green tissue. It appears on the upper, outer leaves facing south or west, and the leaf around it stays firm.
Will sunburned leaves turn green again?
No, sunburned tissue is dead and stays pale or brown. Keep the burned leaves attached through summer, because they shade the growth beneath them. Trim them in October once new leaves have formed and the risk of fresh burn has passed.
Which outdoor plants handle full UAE sun?
Four plants from hot, dry regions handle it well: bougainvillea, oleander, desert rose and date palm, all tolerant of full exposure once established. Heat tolerant species for an exposed bed can be compared in the outdoor plants collection before anything goes into the ground.