Blossom End Rot

Blossom end rot is not a pathogen. It is a calcium-uptake disorder that develops when fruit tissue at the blossom end (opposite the stem) is starved of calcium during rapid cell division early in fruit development. Calcium is abundant in most garden soils; the problem is translocation, not supply. Water carries calcium from roots into actively growing tissue. When soil moisture fluctuates sharply, the plant prioritizes vegetative growth, and expanding leaves outcompete young fruit for available calcium. The result is localized cell death at the blossom end that turns tissue brown, leathery, and sunken.

Tomatoes are the most frequently affected crop, but the same mechanism damages peppers, watermelons, summer and winter squash, and melons. First fruits of the season carry the highest risk because the plant is in rapid early growth and irrigation habits are still being established. A stretch of dry weather followed by a heavy watering event is a classic trigger. High nitrogen fertility compounds the problem by pushing vegetative growth faster than calcium can be translocated to fruit.

Calcium sprays are widely sold as a remedy, but extension research from land-grant universities consistently shows that foliar calcium applications provide little benefit when the underlying cause is irrigation inconsistency. The most cost-effective control is also the most direct: stable soil moisture throughout the growing season. Mulching to moderate soil temperature swings, combined with drip irrigation on a timer, eliminates the disorder in most home garden situations. Affected early fruits should be removed; later fruits produced under consistent moisture will be normal. No varieties with documented resistance to this disorder are currently listed.