Greetings, dedicated gardener. We appreciate your desire to understand our nutritional needs. To flourish and produce the magnificent blooms you so admire, we require a specific balance of elements from the soil. Here is our perspective on the best sustenance for our well-being.
From our roots' point of view, the three numbers on a fertilizer bag (the N-P-K ratio) are a menu. We need a balanced diet for overall health. Nitrogen (N) is crucial for our vibrant green leaf production, which powers our entire system through photosynthesis. Phosphorus (P) is the key to strong root development and, most importantly, bountiful and large flower blooms. Potassium (K) ensures our overall systemic health, aiding in disease resistance and the efficient use of water. A fertilizer labeled 10-10-10 or 12-4-8 provides a wonderful, balanced foundation for our growth.
For many of us, particularly the Bigleaf varieties (Hydrangea macrophylla), the conversation about fertilizer is deeply intertwined with the soil's pH. The availability of aluminum in the soil dictates our bloom color. In more acidic soils (pH below 6.0), aluminum is readily available, and our blooms will tend toward beautiful blues. In more alkaline soils (pH above 7.0), aluminum is locked away, and our blooms will be shades of pink. Therefore, the "best" fertilizer for us sometimes depends on the color you wish to see.
For general health and robust growth, a slow-release, balanced granular fertilizer formulated for shrubs and trees is ideal. It provides a steady supply of nutrients without the risk of burning our delicate roots. For those seeking to influence our bloom color, specialized formulas exist. To encourage pink blooms, a fertilizer higher in phosphorus (e.g., 15-30-15) and with added lime to raise the soil pH is beneficial. To encourage blue blooms, a fertilizer rich in potassium (e.g., 10-5-20) and containing sulfur or aluminum sulfate to lower the soil pH is what we need. Organic options like well-composted manure, compost, or bone meal are also excellent, gentle ways to feed us.
Please do not feed us year-round. The best time to provide fertilizer is in early spring as we break dormancy and begin our new growth. This gives us the energy for leaf and stem development. A second, lighter application can be made around the time our flower buds begin to form. However, you must stop fertilizing by late summer. Feeding us too late in the season encourages tender new growth that will be highly susceptible to frost damage when the cold weather arrives.
