Boxwoods (Buxus species) are popular, long-lived evergreens valued for their dense, fine-textured foliage and structural presence in the landscape. Maintaining their characteristic deep green color and compact form depends on proper care, including correct fertilization. Fertilization provides the necessary nutrients to support healthy growth and resilience. Understanding when and how to feed these shrubs promotes a vibrant, well-maintained boxwood planting.
Assessing When Boxwoods Require Feeding
Boxwoods generally do not require heavy fertilization, but visual cues can signal a nutritional deficiency. The most common sign is chlorosis, or the yellowing of leaves, which often indicates a lack of nitrogen, an element vital for chlorophyll production. This yellowing may appear uniformly across older foliage before progressing to the rest of the plant, especially if the deficiency is severe.
Another indicator of nutrient stress is sparse, weak new growth or an overall lack of vigor. Boxwoods may exhibit a natural bronzing or reddish-orange tint during winter due to cold stress, but this color should fade in spring. If discoloration persists into the active growing season, it often suggests the plant is low on nitrogen or experiencing drought stress. A professional soil test provides the most accurate assessment of nutrient levels and soil pH before applying any amendments.
Optimal Seasonal Timing for Fertilization
The best time to fertilize boxwoods coincides with their natural growth cycle. The primary window for feeding is early spring, just before the new growth flush begins, typically in March or early April, depending on the climate. Applying fertilizer at this time ensures that nutrients are available as the plant emerges from dormancy and begins its most active period of growth.
A second, optional application can occur in mid-to-late spring, after the initial burst of new growth has fully expanded. This timing helps replenish the soil’s nitrogen supply, which is quickly depleted by the heavy demands of spring growth. Focusing fertilization efforts in the spring supports the development of dense, vibrant foliage and strengthens the shrub for the coming summer. Boxwood roots are most active when soil temperatures are moderate, making spring an ideal time for nutrient uptake.
Choosing the Best Fertilizer and Application Method
Boxwoods generally benefit from a complete, slow-release granular fertilizer, which provides a steady supply of nutrients over several months. These evergreens utilize nitrogen to maintain their deep green color and density. A balanced NPK ratio, such as 10-10-10, is a common choice, though a formula slightly higher in nitrogen, like 10-6-4, is often recommended.
The shallow, wide root system of a boxwood is susceptible to burning from concentrated fertilizer applications. Granular fertilizer should be broadcast evenly around the shrub’s drip line—the area beneath the outermost branches—and not directly against the trunk. If the boxwood is mulched, the fertilizer should be applied on top of the mulch layer to prevent burning the sensitive surface roots. Following application, the area must be thoroughly watered to help dissolve the granules and move the nutrients down into the root zone.
Why Late-Season Fertilizing Must Be Avoided
Fertilizing too late in the growing season can severely harm the boxwood by disrupting its natural hardening-off process. This practice should be avoided from mid-summer onward, with a general cutoff date around July. Applying nitrogen-rich fertilizer in late summer or early fall encourages a flush of tender, new vegetative growth.
This late-season growth does not have sufficient time to mature and develop the necessary cellular structure to survive cold temperatures. When the first hard frost arrives, this soft tissue is easily damaged, leading to severe winter injury, dieback, and browning. Stopping fertilization in mid-summer prevents this vulnerable growth and ensures the plant enters dormancy in a resilient state.