Bone meal is a slow-release organic fertilizer created by grinding steamed animal bones, typically from cattle or fish. This powder is a natural source of multiple minerals that enhances soil fertility. Bone meal does contribute calcium to the soil. However, it is most valued for its high concentration of phosphorus, which determines its primary use in gardening.
Bone Meal’s Primary Function as a Phosphorus Source
The main reason bone meal is utilized is its high percentage of phosphorus, the “P” in fertilizer N-P-K ratios. Commercial bone meal often features a high middle number, such as 3-15-0, signifying its richness in phosphorus compared to nitrogen and potassium. Phosphorus is crucial for below-ground and reproductive growth. It stimulates the early formation of robust root systems and promotes the development of root hairs. An adequate supply supports the transition from vegetative growth to flowering and fruiting, ensuring a more abundant harvest. Since the phosphorus in bone meal is not immediately water-soluble, it breaks down slowly over several months, providing a steady, long-term supply.
The Role of Calcium in Bone Meal
Bone meal is a concentrated source of calcium, typically containing between 20% and 25% calcium by weight. This mineral plays a structural role in plants, helping to form strong and rigid cell walls. Sufficient calcium is important for preventing physiological disorders in developing fruit, such as blossom end rot in tomatoes and peppers. This issue occurs when a localized calcium deficiency prevents cell walls from forming properly.
Despite its high calcium percentage, bone meal is not the fastest or most efficient way to correct a severe calcium deficiency. The calcium is primarily bound up as calcium phosphate, which is highly insoluble in water. This means it dissolves and becomes available to plants very slowly. For a quick calcium boost or to rapidly adjust soil pH, amendments like agricultural lime or gypsum are preferred due to their higher solubility.
Maximizing Nutrient Release Through Proper Application
To ensure plants can access the phosphorus and calcium within bone meal, proper application is essential. Since the nutrients are not water-soluble, sprinkling the powder on the soil surface is ineffective and can attract pests. For the best results, bone meal must be thoroughly mixed into the soil when preparing planting holes or beds. This allows soil microbes and acids to break down the particles.
The effectiveness of bone meal relies heavily on the soil’s acidity, performing best in slightly acidic to neutral soil (pH 6.0 to 7.0). In highly alkaline soil (pH above 7.0), the compounds become more insoluble, locking up the phosphorus and calcium. Conversely, in very acidic soil, soluble phosphorus can bind with elements like aluminum and iron, reducing its availability. Therefore, a soil test to confirm the pH level is necessary before application.