The most commonly planted narrowleaf evergreen shrubs are yew, juniper, arborvitae, and false cypress. Popular as foundation plants, these shrubs often need yearly pruning to control their size. To save time and energy, plant dwarf and slow-growing varieties, which need less attention but are more expensive because of the time it takes for them to reach a saleable size in nurseries.
Proper pruning can dramatically control plant size for many years as demonstrated by two identical yews grown in Ohio. A yew planted in 1945 at the Ohio State Agricultural Research and Development Center and left unpruned grew to exceed 27 feet wide and 7 feet tall in 32 years. With yearly thinning, a similar plant reached only 5 feet wide and 2½ feet tall. The pruned shrub occupied its place in a home landscape for decades, but if it had been left unpruned it would have outgrown the space during its first 10 or 15 years.
Keep yews and other narrowleaf evergreens compact and natural-looking by thinning the long branches back to a side branch. Repeat this thinning every year or two as needed to maintain the correct size.
The best time to prune is just before new growth begins in spring. In mid to late summer shorten long stems that arise from a second flush of growth. Do not prune heavily in summer; new growth may not sprout until spring and the exposed pruning cuts will look unsightly. It is best to prune these evergreens early enough in the growing season so that new growth can quickly fill in.
Pruning Upright Narrowleaf Evergreen Shrubs
Upright evergreen shrubs can be pruned yearly to maintain a controlled, dense, symmetrical, pyramidal shape. Thin outward-growing branches to an inward-growing side stem, which will grow upward and outward toward the light. Maintain one dominant leader; subordinate challenging leaders by thinning them to side branches.
To reduce height, cut the dominant leader or multiple leaders to an inward-growing lateral. Shingle the side cuts by making cuts within the foliage so the cut end is hidden. Remove longer sections of branches at the top than at the base to maintain the tapering shape.
Pruning Foundation Plantings
Narrowleaf evergreens such as yew, juniper, arborvitae, and false cypress are traditionally used as foundation plants. Many broadleaf evergreens such as rhododendron, andromeda, azalea, and holly are also commonly planted. Evergreen shrubs provide year-round greenery, hide the foundation, and blend the house into the landscape. However, they often grow too large, obscuring windows and rubbing against the siding. Yearly pruning is necessary to keep most foundation shrubs in bounds.
Although evergreen foundation plants are often sheared, thinning is a better technique. Shearing encourages a shrub to grow slightly larger every year; a sheared shrub eventually gets too big for a foundation planting and develops a thin shell of foliage with a bare center. Thinning narrowleaf evergreen shrubs keeps them compact almost indefinitely and promotes dense growth and a more pleasing appearance.
Correcting Newly Planted Shrubs
Some commercial plant growers shear the tops and sides of evergreens into a tight shape, intending to develop a dense saleable plant quickly. The new tip growth that results from shearing does not regenerate the whole plant, but is concentrated only on the surface.
This kind of shrub needs corrective thinning during the first or second year after planting. Reach into the plant and thin some of the closely spaced side branches. This allows more light into the center of the plant and encourages more natural growth and a less rigid outline. By the third year the shrub will have a looser shape.