Is Tomato Blossom-End Rot a Calcium Deficiency?
Dark sunken tissue at the blossom end often reflects disrupted calcium transport caused by moisture, roots or salinity—not simply low soil calcium.
Recognize the typical symptom
Blossom-end rot begins as water-soaked tissue at the flower end, then becomes dark, sunken and leathery. Secondary organisms may colonize it, so distinguish the disorder from infectious fruit diseases and sunscald.
Available calcium may not reach fruit
Calcium moves mainly with water flow. Dry-wet swings, root injury, salinity and excessive nitrogen or potassium can restrict delivery to rapidly expanding fruit, even when the root zone contains calcium.
Stabilize moisture and salinity first
Use smaller, even irrigations and avoid fully drying the root zone before saturation. Monitor drainage and electrical conductivity under cover; mulch can reduce outdoor temperature and moisture swings.
Prevent nutrient competition
High ammonium, potassium or magnesium can compete with calcium uptake. Match formulas to crop stage, avoid concentrated fertilizer pulses and maintain suitable root-zone pH.
Judge recovery on new fruit
Damaged fruit will not heal and may be removed early. Improvement should be assessed on new fruit; repeated symptoms justify testing water, substrate or soil.
