A hedge is simply a group of shrubs planted in a row. This “living wall” provides privacy without the severity of a wood or brick wall. Trimming the shrubs keeps them in shape and encourages healthy new growth. The goal of hedge trimming is to make the shrubs blend into each other and look like one continuous plant.
If you are planning to plant a hedge, consult a knowledgeable nursery person about the best hedge choices for your area. Plan carefully, since when you plant a hedge, you are committing yourself to long-term maintenance.
Use pruning shears for the best results. They cut cleaner and closer than electric trimmers, which can damage the branches. For very thick branches, you may need to use a pruning saw.
As a general rule, trim a hedge after the first flush of spring growth. This should keep the plants looking well shaped through the summer season.
Trim established hedges often. A good rule of thumb is to cut back 6 inches for every foot of new growth. Very slow-growing shrubs like boxwood need trimming sooner. A rapid grower like privet may require several prunings a year.
Keep flowering time in mind when pruning flowering shrubs. Spring-blooming forsythia, for example, should not be pruned after early summer or next year’s flowers will be lost.
Start shaping your hedge in the third year after planting. The shape will largely depend on the type of shrub. A shrub’s natural growth pattern is your best guide.
Keep the trim natural-looking, with a slightly rounded or pointed top, and sides that taper so the top of the plant is a little narrower than the bottom.
Avoid making straight vertical sides and flat tops. This style not only looks unnatural, it is likely to cause the shrubs to thin out at the bottom and be damaged by snow.
If possible, start trimming your hedge while the shrubs are still young. You can create sturdier plants and train them so there are no holes in your hedge.
At planting time, cut back deciduous shrubs at least 6 inches. This will encourage them to send out lower branches and keep the hedge thick.
Near the end of the plants’ first season or before the buds break in the next season, cut back half of the new growth. Do this again the next year.
Do not trim evergreens at all when they are first planted. After the first couple of years, trim very lightly. Be careful not to overdo evergreen trimming, since many needle-bearing shrubs do not easily regenerate new growth from old wood.
Rejuvenating an Old Hedge
In the spring before buds have broken, use loppers to remove a third of the oldest branches. This will open up the plant to sunlight and encourage new growth.
Cut to the ground any long stems that grow out of the hedge. Use hand pruners to thin stems further; trim the oldest branches away.
Follow up trimming with a fertilizer appropriate to the plant variety.
Consider replacing an old evergreen hedge if it is in bad shape, since most evergreens cannot put on new growth in the same way as a deciduous shrub. Arborvitae and yew are exceptions to this rule and may be candidates for rejuvenating.