Blossom End Rot
Disease · Commonly affects: Tomato, Pepper, Eggplant, Summer squash, Watermelon, Cucumber
Blossom end rot is a physiological disorder, not an infection caused by a fungus, bacterium, or insect, so it does not spread from plant to plant. It matters to home gardeners because it ruins the fruit just as it begins to size up and ripen, often on the first and most anticipated harvest of the season.
How to identify it
Look for a small water-soaked spot at the blossom end of the fruit, meaning the bottom opposite the stem, that enlarges into a sunken, leathery patch turning tan to dark brown or black. On tomatoes the lesion is usually flat and dark, while on peppers it tends to be a lighter tan sunken area. The spot may later be colonized by dark surface molds that move in on the already damaged tissue, but those molds are secondary and not the cause.
Damage
The disorder ruins the affected fruit, making the blossom end inedible even though the rest of the plant looks healthy and keeps growing. It reflects a shortage of calcium reaching the developing fruit, which is usually driven by uneven soil moisture rather than a true lack of calcium in the soil, and it can affect a large share of a picking during hot, dry, or erratically watered stretches.
Prevention
Keep soil moisture even by watering deeply and consistently and mulching with straw, shredded leaves, or grass clippings to buffer swings between wet and dry. Test your soil and adjust pH into the roughly 6.5 range so existing calcium stays available, and avoid heavy applications of high-nitrogen fertilizer that push fast leafy growth at the fruit's expense. Space plants for good airflow and drainage, harden off transplants, and avoid setting them out into cold soil, since chilled or stressed early roots take up calcium poorly.
How to manage it
Because this is a moisture and nutrient disorder rather than a pest, control is cultural: pick off and discard affected fruit so the plant redirects its energy to sound fruit, and correct the underlying watering pattern with deep, regular irrigation. Cultivate shallowly and stay well away from the root zone, since cutting feeder roots interrupts calcium uptake, and maintain a steady mulch layer to hold moisture even. Plants often recover on their own and set clean fruit later in the season once soil moisture stabilizes and the weather steadies.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.