Neglect regular pruning, though, and a wall of evergreen foliage soon looms over your garden. Severe pruning of boxwoods can have mixed results, but you may be able to safely cut the shrubs back by 2 to 3 feet depending on their size, their health and the time of year you prune.enewing Boxwood. Though Viette's Beautiful Gardens in Virginia reports that vigorous boxwoods can survive after being cut to within 2 feet of the ground, renewal pruning is most often recommended for an overgrown boxwood.