The Japanese Boxwood (Buxus microphylla japonica) is a dense evergreen shrub recognized for its small, glossy leaves and structural versatility in the landscape. It is often selected for formal hedges or maintained as a specimen plant. Successfully incorporating Japanese Boxwood depends on correct initial planting distances. Planting too close leads to health issues, while planting too far apart delays the desired aesthetic outcome.
Understanding Mature Size and Growth Rate
Determining the appropriate spacing begins with understanding the plant’s ultimate size and how quickly it reaches it. Japanese Boxwood typically matures to 4 to 6 feet tall and equally wide, though specific cultivars may be smaller or larger. This potential mature spread dictates the minimum distance required for the long-term health of an individual plant.
The growth rate of Buxus microphylla japonica is slow to moderate, making it one of the faster-growing varieties within the Boxwood genus. It usually reaches a functional size for hedging within three to five years. Since the shrub is relatively slow to fill in gaps, precision at planting time is necessary, as mistakes can take several years to correct.
Even if constantly pruned, the root system and base will expand toward the mature width. Planting must allow enough physical space for the root zone to develop unhindered. Failing to account for this width leads to competition for nutrients and moisture, weakening the plants over time.
Specific Spacing Calculations for Different Goals
The distance between Japanese Boxwood plants must be tailored to the specific design goal, whether that is a continuous, formal hedge or a standalone shrub. Spacing is measured from the center of one plant to the center of the next. The core principle involves planting at a fraction of the mature width to achieve the desired density and speed of closure.
For creating a dense, formal hedge, plants must be spaced so their canopies grow together quickly, forming a solid green wall. Space the shrubs at approximately one-half to two-thirds of their mature width. For instance, if the selected variety has a mature spread of 4 feet, planting the centers 2 to 2.5 feet apart will cause them to knit together into a continuous hedge within a few seasons.
A specimen planting requires wider spacing to allow the plant to achieve its natural, rounded shape. Plants should be spaced at or near their full mature width, typically 4 to 6 feet apart. This wider spacing ensures adequate air circulation around the shrub, which helps prevent fungal issues.
For an extra-dense screen, planting in two staggered rows offers a solution. Space the plants in the first row according to the dense hedge formula. The second row is planted at the same spacing, but the plants are offset by half the distance, creating a triangular pattern for maximum density.
Preparation and Planting Techniques
Once the correct spacing has been calculated, preparation of the planting site is the next practical step. Japanese Boxwood requires well-drained soil and will struggle in areas where water pools. Amending heavy clay soils with organic matter like compost improves drainage and structure before planting.
The planting hole should be dug two to three times wider than the root ball, but no deeper. Digging wide holes encourages the roots to spread horizontally into the surrounding native soil, promoting robust establishment. A hole that is too deep can cause the plant to settle too low, leading to poor root development.
When placing the shrub, ensure the top of the root ball remains slightly above the surrounding soil level, with the root flare visible. This prevents the stem from being buried, which can lead to rot and plant decline. Backfill the hole with the excavated soil, tamping gently to remove air pockets, and water thoroughly immediately after planting to settle the soil around the roots.
Pruning and Maintenance for Density
Ongoing maintenance, particularly pruning, plays a significant role in realizing the aesthetic goal of the chosen spacing. After planting, a light tip pruning of the outer branches encourages new growth and heavier branching, accelerating density and canopy closure. This initial shaping helps plants start knitting together at the correct height and width.
The method of pruning must align with the planting goal: formal hedges are maintained by shearing, which keeps a sharp, formal shape and is necessary for uniform, closely spaced hedges. Specimen plants benefit from selective pruning, or thinning, which involves removing individual branches to help the plant maintain a natural, rounded form.
Even in dense hedge plantings, it is important to occasionally thin the interior branches to improve air circulation and light penetration. Boxwood foliage is often so thick that it shades out the interior, leading to dead patches if not thinned. Maintaining a slightly wider base than the top, known as a wedge shape, ensures sunlight reaches the lower leaves, keeping the foliage dense to the ground.