What Causes Blossom End Rot (and How to Stop It)
Blossom end rot is caused by a temporary shortage of calcium reaching developing fruit, most often because soil moisture fluctuates or roots are stressed. The practical fix is steady watering, healthy roots, and avoiding unnecessary fertilizer or soil amendments.
The disorder begins as a small, water-soaked area at the blossom end, opposite the stem, then becomes dark, dry, and sunken. It is most common on the first fruits of tomatoes, peppers, squash, and eggplant. It is not contagious and does not spread from one fruit to another.
Even when soil contains adequate calcium, a plant may not move enough of it into rapidly growing fruit during drought, flooding, root disturbance, or uneven watering. Water deeply at the root zone and prevent severe dry-downs. A mulch layer helps make moisture conditions more stable.
Do not assume the solution is to add calcium. Extra amendments may be unnecessary or may disrupt soil balance, especially when calcium is already adequate. A soil test through a local Cooperative Extension program can identify pH and nutrient conditions before you add lime, gypsum, or fertilizer.
Protect roots. Avoid cultivating deeply near plants, planting into poorly drained soil, or allowing containers to become root-bound and repeatedly dry out. In containers, use a sufficiently large pot with drainage holes and a consistent watering routine, since potting media dry much faster than garden soil.
Excess nitrogen, high salt levels, and very rapid vegetative growth can contribute to the conditions that favor blossom end rot. Follow soil-test guidance, avoid overfertilizing, and use fertilizer according to its label. If you suspect a fertilizer or irrigation-water issue, local Cooperative Extension can help interpret a soil or water test.
Affected fruit will not heal, so remove it once the diagnosis is clear. Keep the plant growing steadily, because later fruit often develops normally after moisture management improves. If the problem continues despite consistent watering, investigate root disease, poor drainage, or soil-test results.
Frequently asked questions
Can I save a tomato that already has blossom end rot?
No. The damaged area will not recover. Remove the affected fruit so the plant can direct resources to healthy new fruit.
Does blossom end rot mean my soil has no calcium?
Usually not. The more common issue is inconsistent calcium movement within the plant because of fluctuating moisture or root stress.
Should I spray calcium on the leaves or fruit?
Foliar applications are not a dependable correction for blossom end rot. Focus first on consistent soil moisture, root health, and soil-test-based nutrient management.
General guidance for US home gardens. Conditions vary by region and season; check with your local Cooperative Extension office for site-specific advice. Page updated Aug 4, 2026.