Why Is My Watermelon Getting White or Bleached Patches on the Skin?

Developing watermelons that show white, bleached or pale yellow patches on the side of the fruit exposed to direct sunlight are suffering from sunscald — essentially sunburn on the fruit skin. The affected tissue is cooked by intense direct sun, the skin cells die and turn white or papery, and the patch is a permanent cosmetic damage to that fruit. In severe cases the affected skin may crack and allow secondary rot to enter. Understanding how to prevent sunscald is straightforward once you know what causes it.

Exposed fruit after defoliation

Watermelon fruits that are tucked under the canopy of leaves are naturally shaded from the most intense midday sun. When disease or insect damage removes large areas of foliage — or when you prune too aggressively — fruits become exposed to direct overhead sun. In hot climates with very intense summer sunshine, even a few hours of direct exposure during the hottest part of the day is enough to scald the skin. Keep plants as healthy and leafy as possible throughout the growing season to maintain natural canopy shade.

Protecting exposed fruits

If a fruit is already exposed and you are in a hot sunny climate, you can shade it by draping a broad leaf over it, laying a piece of agricultural fleece loosely over the fruit, or using a cardboard shade. The goal is to interrupt the direct beam of the midday sun on the fruit's surface while still allowing airflow around it. Avoid wrapping tightly — trapped heat is also damaging.

Moving fruits on the vine

Watermelon fruits often rest on the soil. If they have settled in a position with the green-striped side up and the pale resting spot on the bottom, they are correctly positioned for natural shading. Do not move fruits unnecessarily — the skin on the formerly shaded side is more sensitive than the side that has been gradually exposed to sun, and rapid relocation can cause worse sunscald than leaving the fruit in place.

Using straw mulch under fruits

Fruits resting directly on bare soil in hot weather can be scorched on the bottom from heat radiating up from the soil. Placing a small pad of straw or a tile under each developing fruit protects it from soil heat and also prevents surface rot where the fruit contacts the soil.