With Buxus microphylla var. japonica 'Green Gem' (Boxwood 'Green Gem'), you get a compact, dense, rounded evergreen shrub with glossy green foliage that keeps good color through winter. Use it to define a low hedge, edge a walk, anchor a foundation bed, or add year-round structure to mixed plantings. Its naturally tidy shape takes light shearing well, so you can keep it formal or let it grow into a soft globe.
Plant it in well-drained soil and water regularly during establishment. Once rooted in, keep moisture consistent, especially through dry spells and before winter, since winter sun and wind can dry foliage. Mulch over the shallow roots to moderate soil temperatures and reduce drying. Avoid aggressive cultivation close to the plant; instead, top-dress with compost or a thin layer of mulch.
Give it sun to shade; in warmer locations, afternoon shade helps reduce stress and winter bronzing. Plan for a mature size around 24-36 inches tall with a similar width, and provide a bit of air flow around the plant. Prune after spring growth flushes, and avoid late-season pruning that can encourage tender growth going into cold weather. Deer and rabbits typically leave it alone, making it a reliable choice where browsing is a concern.