Understanding and Preventing Blossom-End Rot in Tomatoes

What Is Blossom-End Rot?

If your tomato or pepper fruits develop a black, sunken lesion at the blossom end—especially when the fruit is only about an inch long—you’re likely seeing blossom-end rot. This common disorder isn’t caused by a pathogen but by a calcium deficiency in the developing fruit, often triggered by inconsistent watering.

Why Does It Happen?

Calcium moves through the plant via water uptake. When watering is erratic—either too shallow or too excessive—roots can’t absorb calcium efficiently. Shallow watering encourages roots to stay near the surface, where they’re vulnerable to drying out. Overwatering displaces oxygen in the soil, impairing root function and nutrient uptake. Most U.S. soils are naturally low in calcium, compounding the problem.

Practical Solutions

• Water deeply and consistently. Aim for 1.5 inches of water per week, delivered in one or two deep soakings rather than daily light sprinklings. This encourages deep root growth where nutrients are more available.
• Mulch heavily. Use straw or dried grass clippings to conserve soil moisture and reduce temperature fluctuations.
• Add calcium sources. Crushed eggshells worked into the soil provide a slow-release calcium supply. Alternatively, a foliar spray of 1 tablespoon Epsom salts (magnesium sulfate) per gallon of water can enhance the plant’s ability to take up calcium and other nutrients.
• Incorporate Epsom salts at planting. Adding 1–2 tablespoons per planting hole in spring has been shown to reduce blossom-end rot incidence.

Quick Checklist for Healthy Fruit

1. Test soil pH; aim for 6.0–6.8.
2. Water deeply 1–2 times weekly.
3. Mulch 2–3 inches thick.
4. Apply calcium amendments early.
5. Avoid high-nitrogen fertilizers that promote foliage over fruit.

With consistent moisture and adequate calcium, your tomatoes and peppers should develop firm, healthy fruit all season.