To plant a formal hedge, space shrubs more closely than usual, typically setting them only one-half to one-third as far apart from each other as the planting directions indicate. However, do leave the full recommended spacing between plants and a walkway or other permanent barrier. Otherwise, you'll end up doing more than the desirable amount of pruning to keep the plants in bounds, and the hedge will show a lot of bare wood.
In most cases, you'll prune shrubs at planting time to force branching and encourage a thick hedge that's foliaged to the ground. Cut back larger deciduous plants by about a third, smaller ones to within several inches of the ground. Also cut back fast-growing broad-leafed evergreen plants, but less severely than deciduous sorts. Don't head back slow-growing broad-leafed evergreens or conifers; just shorten their lateral branches.
During the rest of the first year, don't prune again except to trim overly vigorous shoots. In subsequent years, cut back new growth by about half to encourage dense branching. Prune after the initial spring growth flush, then again later in the season if needed. In regions where plants are subject to frost damage, don't prune after midsummer.
No matter what the hedge's shape, slope the sides so that the bottom is wider than the top. This allows sunlight to reach the entire hedge surface, stimulating growth all over the plant.
Sloping the sides of a hedge
Slope the sides of a clipped or sheared hedge so that the bottom is wider than the top, allowing sunlight to reach the entire hedge surface. Without adequate light, the lower leaves and stems will die. In snowy climates, a peaked or rounded top will keep snow from accumulating on the hedge and possibly damaging it.