Blossom End Rot

• Dark, sunken, leathery patch on the bottom (blossom end) of fruit — typically first fruit of the season
• Affected area starts as a small pale spot, then expands and turns brown to black
• The rest of the fruit may ripen normally while the end rots
• Most common on the first flush of tomatoes, peppers, or squash in a season
• Secondary mold often colonizes the damaged tissue

Blossom end rot is a physiological disorder, not a disease or pest. It results from insufficient calcium reaching developing fruit tissue. The calcium is usually present in the soil — the issue is the plant's ability to move it. Irregular watering (alternating dry and wet soil) disrupts calcium uptake. Root damage from deep cultivation, excessive ammonium nitrogen, and soil that swings from dry to saturated all contribute.

1. 01Water consistently and deeply — irregular moisture is the most common cause
2. 02Mulch around plants to maintain even soil moisture between waterings
3. 03Avoid deep cultivation around plant roots — root damage impairs calcium uptake
4. 04Test soil before adding calcium amendments — most garden soils have adequate calcium
5. 05If soil calcium is genuinely low (below 1000 ppm), add ground limestone (calcitic lime) or gypsum
6. 06Foliar calcium sprays may reduce BER incidence when applied at fruit set, though results vary
7. 07Remove affected fruit — the plant can direct resources to subsequent fruit

If blossom end rot recurs heavily despite consistent watering and mulching, a soil test from your local extension lab can confirm whether calcium or pH is actually the issue — and many extension offices offer testing at low cost.

• Blossom End Rot of Tomatoes and Peppers— University of Minnesota Extension
• Blossom End Rot— Clemson Cooperative Extension