Hydrangeas are popular garden plants known for their abundant blooms and diverse colors. Understanding proper fertilizer ratios is important for their health and flowering. This guide explains how to select and apply the correct nutrient blends.
Understanding Fertilizer Numbers
Fertilizer labels display three numbers, such as 10-10-10, representing the percentage by weight of Nitrogen (N), Phosphorus (P), and Potassium (K). These N-P-K numbers are always presented in this order. The remaining percentage consists of minor nutrients or fillers.
Nitrogen supports leafy growth and green color. Phosphorus is important for root development and blooming. Potassium enhances overall plant health, aiding in disease resistance, water regulation, and stress tolerance.
Selecting the Right Ratio for General Hydrangea Health
For general hydrangea health and robust growth, a balanced fertilizer ratio like 10-10-10 NPK is suitable. This formula provides equal proportions of nitrogen, phosphorus, and potassium, ensuring necessary nutrients for healthy development.
To encourage abundant blooms, a fertilizer with higher phosphorus is beneficial. Too much nitrogen leads to excessive leafy growth at the expense of flower production. If your hydrangeas have lush foliage but few flowers, reducing nitrogen may be helpful.
Adjusting Ratios for Hydrangea Color
The flower color of Hydrangea macrophylla and Hydrangea serrata is influenced by soil pH. In acidic soil (pH below 6.0), blooms tend to be blue. This blue coloration occurs when aluminum, naturally present in most soils, becomes available for absorption.
To achieve blue flowers, add amendments like aluminum sulfate to lower the soil pH. Fertilizers low in phosphorus and high in potassium, such as a 12-4-8 ratio, also encourage blue blooms by increasing aluminum availability. Conversely, in alkaline soil (pH above 6.5), hydrangea flowers turn pink.
To promote pink blooms, apply garden lime to raise the soil pH. This adjustment reduces aluminum availability, favoring pink coloration. White hydrangeas do not change color regardless of soil pH. Achieving a desired color takes time and consistent application of amendments, often over several weeks or months.
Timing and Applying Hydrangea Fertilizer
The optimal time to fertilize hydrangeas is early spring, as new growth emerges and after the last frost. For reblooming varieties, a second application in early summer supports continued flowering. Avoid fertilizing after mid-July or early August, as late-season fertilization stimulates tender new growth vulnerable to winter damage.
When applying granular fertilizer, sprinkle it evenly around the plant’s drip line, the area beneath the outer edge of its branches. Avoid direct contact with stems or leaves, as this can cause fertilizer burn. Always water thoroughly before and after applying fertilizer to distribute nutrients and prevent root damage.
Troubleshooting Common Fertilization Problems
Incorrect fertilization practices can lead to several issues for hydrangeas. One common problem is fertilizer burn, which results from over-application of nutrients. Symptoms include scorched or browned leaves.
Another frequent issue is a lack of blooms, often due to excessive nitrogen. Too much nitrogen promotes lush foliage growth at the expense of flower development. If this occurs, consider skipping fertilization for a season or using a product with a lower nitrogen content. Nutrient deficiencies can also arise from under-fertilization or incorrect nutrient ratios, impacting overall plant health and vigor.