Boxwood is a popular, dense evergreen shrub highly valued in landscaping for its fine texture and ability to be shaped into formal hedges and topiaries. The defining characteristic that dictates how a boxwood is cared for is its root structure, which is uniquely shallow and highly fibrous. This architecture makes the shrub sensitive to environmental factors like soil moisture and temperature fluctuations.
Defining the Boxwood Root System
The boxwood root system is characterized by its high density and shallow profile, forming a wide, dense mat rather than a deep taproot structure. The majority of the nutrient and water-absorbing roots remain concentrated within the top six to eighteen inches of the soil surface. This dense aggregation of fine, fibrous roots allows the boxwood to efficiently capture surface moisture and nutrients.
The roots prioritize horizontal spread over vertical penetration, often extending well past the shrub’s canopy drip line. This means a mature boxwood’s root zone can be significantly wider than the plant is tall. Because the roots are not aggressive or woody, they pose no structural threat to nearby foundations, walkways, or underground pipes. Their fibrous nature also makes established boxwoods easier to transplant than many other shrubs with deep root systems.
Caring for Shallow Roots (Watering and Mulching)
The root system’s close proximity to the soil surface leaves the boxwood vulnerable to drying out and extremes in soil temperature. During hot, dry periods, moisture in the top few inches of soil evaporates quickly, immediately impacting the plant’s ability to hydrate. This requires a targeted watering strategy to ensure the roots remain consistently moist without becoming waterlogged, which can lead to root rot.
Newly planted boxwoods should receive approximately one inch of water per week, especially during the first 18 months of establishment, focusing the application directly over the root zone. Established plants require supplemental watering during periods of drought, often benefiting from a slow, deep soaking that encourages healthy root function. Using drip irrigation or a soaker hose is the most effective method, as it delivers water directly to the soil and avoids wetting the foliage, which helps prevent certain fungal diseases.
Applying an organic mulch layer manages the shallow roots effectively. A two-to-three-inch layer of shredded bark or compost helps insulate the root zone from heat stress in the summer and cold in the winter. Mulch also reduces surface evaporation, conserving soil moisture and stabilizing the temperature around the root mass. Apply the mulch widely, extending it out to the edge of the canopy, but keep it pulled back a few inches from the shrub’s main stem to prevent moisture buildup and decay at the crown.
Planting and Installation Best Practices
Because boxwood roots are prone to water stagnation, planting techniques should prioritize excellent drainage to prevent root suffocation. The recommended practice is to plant the boxwood slightly high, positioning the top of the root ball about one to two inches above the surrounding grade. This slight elevation ensures that water drains away from the crown, allowing the soil to settle without the plant sinking too deeply.
Before placing the shrub into the planting hole, which should be two to three times wider than the root ball, gently loosen the fibrous root ball. If the roots are tightly bound, teasing them out encourages them to grow horizontally into the surrounding soil rather than continuing to circle within the original container shape. Backfilling the hole with native soil and gently tamping it down removes air pockets while maintaining the elevated position of the crown. Proper drainage is the most important factor during installation; in areas with heavy clay soil, planting on a slightly raised berm can further improve water runoff and protect the root system.