Calgary Boxwood (Buxus ‘Calgary’) is a popular evergreen shrub, valued for its hardiness and structure. It offers year-round visual interest and is a choice for various landscape designs. Understanding its characteristics, planting, care, and common issues ensures successful growth.
Characteristics of Calgary Boxwood
Calgary Boxwood, also known as Korean Boxwood, is a broad-leaved evergreen shrub known for its compact, rounded habit. It grows dense and rounded, reaching 2 to 3 feet tall and wide. Its small, glossy, oval dark green leaves, typically ½ to 1 inch long, remain vibrant year-round.
This variety is exceptionally cold hardy, thriving in USDA Hardiness Zones 2 to 9, suitable for regions with harsh winters. It tolerates temperatures as low as -50 to -40 degrees Fahrenheit but prefers moderate conditions. Its dense foliage, sometimes with inconspicuous creamy white flowers in spring, makes it a choice for formal hedges, borders, accent plantings, and container gardening.
Planting and Establishment
Location selection is key for Calgary Boxwood. It performs well in full sun to partial shade, ideally with four to six hours of direct sunlight daily for compact shape and growth. It adapts to various soil types but requires well-drained soil, as it does not tolerate standing water. Amending heavy clay soils with organic matter like compost improves drainage and aeration.
Plant in spring or fall when temperatures are moderate, allowing roots to establish before extreme temperatures. Dig a hole twice as wide as the root ball and as deep, ensuring the crown sits at or slightly above the soil surface to prevent water pooling. Gently remove the plant from its container, loosen tangled roots, and backfill the hole with original soil, lightly tamping to remove air pockets. After planting, water thoroughly to settle the soil, and apply a 2 to 3-inch layer of mulch around the base to retain moisture and regulate soil temperature.
Ongoing Care and Maintenance
Consistent watering is important, especially during the first one to two years of establishment. During this period, water deeply once or twice weekly, allowing soil to dry slightly between waterings. Once established, boxwood is relatively drought-tolerant but benefits from supplemental watering during dry spells. Ensuring the plant is well-hydrated before ground freeze protects it from winter damage.
Fertilizing can support healthy growth, though it is not always required. A balanced, slow-release granular fertilizer (e.g., 10-10-10 NPK) can be applied once in early spring, and potentially again in late summer. Avoid fertilizing in late summer or early fall, as this encourages new growth vulnerable to frost damage. Apply fertilizer around the drip line, on top of the mulch layer, rather than directly on shallow roots.
Pruning maintains the desired shape and density. Significant pruning is best in late winter or early spring before new growth, removing winter-damaged tips and encouraging a strong spring flush. Light trimming for shape maintenance can occur in late spring to early summer after initial growth. Thinning the canopy by removing select branches improves air circulation and light penetration, reducing fungal disease risk. Use sharp, clean tools for precise cuts and disinfect them between plants to prevent disease spread.
Winter protection is advisable in harsh climates to prevent winter burn and snow breakage. Plant in locations protected from strong winter winds (e.g., east or north side of buildings or fences). For added protection, especially for younger or exposed plants, wrap them loosely with burlap or tie up branches with twine to prevent snow accumulation. Ensuring adequately moist soil before winter also provides root insulation.
Addressing Common Challenges
Calgary Boxwood is generally resilient but can encounter common issues. Pests like boxwood leafminer and spider mites affect foliage. Boxwood leafminer larvae feed inside leaves, causing blisters and discoloration. Spider mites cause stippling and a grayish appearance, especially in hot, dry conditions. Regular inspection and appropriate treatments (e.g., insecticidal soap for mites, specific insecticides for leafminers) manage these pests.
The box tree moth is another invasive pest that can defoliate boxwood; caterpillars are the damaging stage. Hand-picking larvae or using biological pesticides are options for control.
Diseases impact boxwood, often linked to environmental conditions. Root rot, caused by consistently wet or poorly drained soil, leads to wilting, discolored leaves, and plant decline. Proper drainage and avoiding overwatering during planting are primary preventative measures. Fungal issues, such as boxwood blight, thrive in damp conditions with poor air circulation, causing leaf spots and stem lesions. Proper spacing and thinning during pruning improve airflow, reducing disease susceptibility.
Environmental stresses like winter burn or drought stress affect Calgary Boxwood. Winter burn occurs when cold, dry winds desiccate evergreen foliage, especially in sunny, exposed locations, leading to browning. Proper winter protection, including strategic planting and physical barriers like burlap, mitigates this. Drought stress results from insufficient water, causing leaves to yellow and drop prematurely. While established boxwood tolerates some dry periods, consistent moisture during prolonged dry spells is important for overall plant health.