When we plant trees in groves, windbreaks, or other plantings which are intended to develop into large trees unhampered by surroundings, pruning is not necessary. Time To Prune Junipers, yews, arborvitae, and hemlock are usually pruned just before periods of rapid growth, when the pruning cuts will be covered quickly. But they can be pruned any time of the year. Generally speaking, however, it is better to prune before late July or August, so that the new foliage that develops has time to hardened off for winter. This is usually after the first of June.
New buds form behind the pruned off growth.
Broadleaf evergreens that bloom in late spring such as boxwood, pyracantha, euonymus, and mahonia should be shaped in the winter or early spring to stimulate good new growth and bloom on the new wood.