Sunburn

📖 Overview

Sunburn on plants is a straightforward but often misdiagnosed problem: direct sun exposure literally scorches leaf tissue, creating papery, bleached patches that cannot heal. Unlike fungal or bacterial diseases, sunburn leaves no ring of yellowing and causes no spread—it's pure damage from ultraviolet radiation and heat stress concentrated on the sun-facing side of the leaf or fruit. It matters most to gardeners who move indoor plants outdoors abruptly, grow sun-sensitive crops like cucumber and pepper in intense mid-summer conditions, or have tender ornamentals such as young maples and birches exposed to unfiltered afternoon rays. The window of danger runs from late May through August in temperate climates, with peak risk in June and July when day length and solar intensity peak, especially after a cloudy spell when plants have weakened sun acclimation.

The first sign you'll notice is crisp, bone-dry patches appearing overnight or over a few days on the leaf surface or on developing fruit, always on the side facing the strongest sun. These patches are sharply bordered, paper-thin, and often tan or bleached white—never surrounded by a halo of yellow or soft tissue, which would suggest fungal disease. A key way to tell sunburn from a disease is its one-sided distribution: if only the south or west-facing leaves are affected and the plant's shadowed side looks healthy, you've almost certainly got sunburn, not a pathogen spreading through the plant.