A new and distinct cultivar of Buxus plant named ‘WINTER JADE’ is disclosed, characterized by an upright plant habit with dense branching and dense foliage cover. Plants have shown resistance to the normal diseases and pests of Boxwood. Foliage is dark lush green. Plants have been observed to tolerate temperatures between 0 degrees F. to 110 degrees F. without negative effects. The dark green foliage color is maintained in both winter and summer under both low and high temperatures. The new cultivar is a Buxus, suitable for ornamental garden purposes.