Calcium for Plants: Preventing Blossom End Rot & Building Strong Cell Walls

Beyond N-P-K, calcium is essential for plant cell division, root development, and preventing disorders like blossom end rot (common in tomatoes, peppers, squash). Deficiency shows as yellowing leaves, poor roots, brown spots, and small, malformed fruit.

Organic Calcium Sources

Regular composting (burying scraps, leaf mold, grass clippings) usually supplies ample calcium. For targeted supplementation:

• Calcitic lime – raises pH while adding calcium.
• Gypsum (calcium sulfate) – adds calcium without altering pH.
• Bone meal – bonus: supplies phosphorus too.
• Soft rock phosphate – slow-release calcium and phosphorus.
• Wood ash – calcium + potassium. Never use charcoal ash—toxic.

Testing & Application

Use a home soil test kit (under $10) to measure calcium and pH. Follow product rates precisely. Bone meal is a cost-effective two-for-one. Compost remains the foundation—feed the soil, and the soil feeds your plants.