Boxwoods are popular evergreen shrubs valued for their dense, year-round foliage and adaptability to shaping. They are generally considered low-maintenance regarding nutrient requirements. While established boxwoods often thrive without annual feeding, fertilization is beneficial when soil quality is poor or when promoting vigorous new growth is the goal. The decision to fertilize should be guided by the plant’s appearance and growing environment.
Assessing When Fertilization is Necessary
Healthy boxwoods display a vibrant, deep green color and maintain dense foliage without signs of stress. Conversely, a plant needing nutrients will show distinct symptoms. The most common indicator is general yellowing, or chlorosis, particularly on older, lower leaves, often pointing to a nitrogen deficiency.
If the leaves appear thinner, smaller than normal, or develop yellow edges, this signals a lack of adequate nutrition. Nutrient-deficient plants may also be more susceptible to bronzing, a discoloration of the foliage, during winter months. Performing a soil test is the most accurate way to confirm specific nutrient imbalances or pH issues before applying any product.
Boxwoods in well-draining, sandy soils are more likely to require supplemental feeding because these soils do not retain nutrients effectively. Newly transplanted shrubs or those in high-stress environments, such as containers, may also benefit from a light application to help them establish or recover. For established, vigorous boxwoods, annual fertilization is unnecessary, as over-fertilization can damage their shallow root systems.
Choosing the Correct Fertilizer Composition
Fertilizer formulas are identified by their N-P-K ratio, representing the percentage by weight of Nitrogen (N), Phosphorus (P), and Potassium (K). Boxwoods benefit from formulas with a higher percentage of nitrogen to support green foliage production. A ratio such as 10-6-4 is often recommended, though a balanced formula like 10-10-10 may be suitable if a soil test indicates adequate nitrogen levels.
Nitrogen is quickly depleted from the soil, especially in sandy conditions, making it the most frequent deficiency. Boxwoods perform best when soil pH is maintained in a slightly neutral to slightly alkaline range, ideally between 6.5 and 7.5. Since nitrogen-rich fertilizers can gradually increase soil acidity, regular soil testing helps maintain the proper pH level for optimal nutrient availability.
Slow-release granular products are preferred because they deliver nutrients steadily over a longer period, minimizing the risk of root burn to the shallow root structure. Products containing micronutrients, such as magnesium, can help enhance the deep green color of the foliage. Organic options, like aged manure or composts, are alternatives that also provide a slow, gentle nutrient release.
Proper Timing and Application Techniques
The most effective time to apply fertilizer is in early spring, just before the shrub begins its new flush of growth. This timing ensures nutrients are available when the plant is actively growing and requires the most energy. Applying fertilizer in late fall can also be beneficial, as it supports root development during cooler months when the roots are still active.
Avoid fertilizing in late summer or early fall, as this stimulates tender new growth that lacks time to harden off before the first frost. This soft, late-season growth is highly susceptible to winter damage and can weaken the entire plant. When applying granular fertilizer, broadcast it evenly across the soil surface, extending out to the shrub’s drip line where the most active feeder roots are located.
The fertilizer should never be placed directly against the trunk or in a thick layer, as this causes stem and root tissue damage. After spreading the granules, thoroughly water the area to dissolve the product and move the nutrients down into the root zone. This step is important for nutrient absorption and preventing the fertilizer from burning the shallow roots.