Blossom End Rot
Calcium deficiency (physiological disorder, not pathogenic)
Overview
Blossom end rot is a calcium-related physiological disorder - not a pathogen - common on tomatoes, peppers, squash, and melons. Irregular watering and root damage limit calcium delivery to expanding fruit, leaving a dark leathery patch on the blossom end. Blossom End Rot is managed first with cultural controls suited to permaculture systems: sanitation, spacing, irrigation style, and resistant planting stock. Causal agent: Calcium deficiency (physiological disorder, not pathogenic). In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Water-soaked spot at the fruit bottom that enlarges into a dark, sunken, leathery lesion. First clusters are hit hardest. Secondary molds may colonize dead tissue but are not the primary cause. Compare several plants and note whether symptoms spread after rain, insect feeding, or wet foliage. Photograph undersides of leaves and cut stems when wilt is present to refine the diagnosis. Rule out simple drought, fertilizer burn, and herbicide drift before assuming a pathogen - abiotic injury often mimics disease.
Environmental Conditions
Hot
Prevention
Build soil organic matter and steady irrigation before fruit set. Avoid cultivating close to roots. Maintain pH in the range that keeps calcium available. Choose less-sensitive cultivars if blossom end rot is chronic on your site. Mulch to reduce splash, clear season-end debris, and avoid working plants when wet. Design beds for airflow and diverse plantings that support beneficial insects without creating permanent humid pockets around susceptible crops.
Management
Water deeply and evenly; mulch to buffer moisture swings. Ease off excess nitrogen that pushes soft growth. Lime acidic soils with low calcium. Remove affected fruit so plants redirect energy. Foliar calcium sprays help only marginally compared with soil moisture management. Prefer drip irrigation, morning watering, and open spacing so leaves dry quickly. Disinfect pruners between cuts on woody plants. Use copper, sulfur, or biological products only as labeled protectants when pressure is high - they rarely reverse advanced infections alone. Destroy (do not casually compost) highly infectious debris.