Bone meal is a traditional organic fertilizer made from steamed and ground animal bones. This slow-release amendment provides minerals, but its effectiveness depends on the specific needs of the plant and existing soil conditions. For dahlias, prized for their spectacular blooms, determining if bone meal is beneficial requires examining its composition and how it supports the plant’s unique growth cycle.
The Critical Role of Phosphorus for Dahlia Tubers
Bone meal is primarily composed of phosphorus (about 15%) and calcium (about 12%). This high concentration of phosphorus is why bone meal is frequently recommended for tuberous plants like dahlias. Phosphorus plays a central role in a plant’s energy transfer system, specifically in the formation of adenosine triphosphate (ATP), which stores and transports chemical energy within cells.
This energy supports strong root and tuber development. Adequate phosphorus levels are necessary for the division and growth of cells that form the dahlia’s storage tubers, ensuring they are healthy for overwintering. Phosphorus also directly encourages abundant flowering and seed production, aligning with the primary goal of most dahlia growers.
The calcium present in bone meal is also beneficial, as it is a structural component of plant cell walls. Strong cell walls help maintain the structural integrity of the plant, contributing to sturdy stems and overall plant health. Focusing on these specific nutrients is necessary because too much nitrogen can promote excessive foliage growth at the expense of flower and tuber development in dahlias.
Proper Application and Timing for Bone Meal
The correct time for applying bone meal is when the tubers are first planted in the spring, ensuring nutrients are available as the plant establishes its root system. Applying it at this time allows the slow-release fertilizer to begin breaking down. The slow-release nature of bone meal means it gradually provides phosphorus over several months, sustaining the plant throughout its long growing season.
The most effective method is to incorporate the bone meal directly into the planting hole or mix it thoroughly with the surrounding soil before planting the tuber. Use approximately one to two tablespoons of bone meal per planting hole, mixing it completely into the soil where the roots will grow. This direct incorporation prevents the bone meal from simply sitting on the soil surface, where it would be largely ineffective and could potentially attract animals.
Avoiding excessive application is important, as too much phosphorus can interfere with the plant’s ability to take up other necessary micronutrients like zinc and iron. Over-fertilization can lead to a buildup in the soil that can be detrimental over time. Once the dahlia has established, a top dressing of bone meal is typically less effective than a liquid fertilizer, and reapplication is generally not needed until the next planting season.
Soil pH and Nutrient Availability
The effectiveness of bone meal relies heavily on the soil’s acidity or alkalinity. Bone meal’s phosphorus is bound in a form that is not immediately water-soluble. Specifically, bone meal works best in soils that are slightly acidic to neutral, with a pH level below 7.0.
If the soil is alkaline (pH above 7.0), the phosphorus tends to remain in an insoluble form, making it largely unavailable for the dahlia roots to absorb. In these high-pH conditions, the nutrient becomes “locked up.” For dahlias, the ideal soil pH is generally between 6.5 and 7.0, a range where nutrient uptake is maximized.
Gardeners should conduct a soil test to determine the existing pH and phosphorus levels before applying bone meal. If the test reveals an alkaline environment, an alternative strategy is necessary, such as using a different form of phosphorus fertilizer or amending the soil with materials like peat moss or sulfur to lower the pH. Understanding this pH dependency prevents wasted effort and ensures the dahlia can utilize the phosphorus.