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Special Cases: Pruning for Particular Purposes
by Karan Davis Cutler
Hedges
No hedge will be successful unless you've chosen a plant or combination of plants that can fulfill your screening needs. Evergreen species with small or medium leaves such as boxwoods (Buxus) are best for formal hedges, as are many conifers, including eastern red cedar and Rocky Mountain juniper (Juniperus virginiana, J. scopulorum), yews (Taxus), arborvitaes (Thuja), and hemlocks (Tsuga).
Almost any shrub or small tree can be part of an informal hedge that is pruned minimally, just enough to ensure dense growth, to control size, and to promote good health. Lilacs (Syringa), species and old garden roses (Rosa), Virginia sweetspire (Itea virginica), hawthorns (Crataegus), witch alder (Fothergilla), alpine currant (Ribes alpinum), flowering quinces (Chaenomeles), and cinquefoils (Potentilla) are a few good deciduous choices. Conifers, hollies (Ilex), and mountain laurel (Kalmia latifolia) can be used as well. You can reduce maintenance by choosing plants that will require less pruning, such as hollies, spruces (Picea), and hornbeams (Carpinus).
As with other plants, when pruning a hedge, remove damaged and dead wood first, then prune for shape and size.
Young hedge plants should be pruned after the first year of growth. In early spring of the second year, remove half of the new growth on deciduous plants, especially if you have a formal hedge in mind, and do that again in the third year. Then begin to shape the hedge. Don't head back new conifers; instead, begin to shape them gently after they've been in the ground for a year or three. Once an informal hedge is established, it shouldn't require much more than maintenance pruning; formal hedges need more care. New England nurseryman and author Lewis Hill believes the best advice for pruning hedges is, "Do it when they look like they need it."
Formal or informal, the most important thing to know about maintaining a healthy hedge is that it must be wider at the bottom than at the top—in other words, shaped like an upside-down V. (This ensures that the bottom branches don't die from being shaded by upper branches.) The top of the hedge can be rounded or flat, but snowbelt gardeners will want to keep it fairly narrow.
Formal, sheared hedges should be wider at the bottom and narrower at the top to allow sunlight to reach lower branches (A), which otherwise would become bare and unsightly (C). In regions with heavy snowfall, hedges with broad flat tops (B, left) may be damaged by the weight of excessive snow accumulation. Hedges clipped in straight lines (B, center) require frequent trimming. Rounded forms (B, right) hinder snow accumulation and require less trimming.
Informal hedges require only a good pair of pruning shears or loppers, as they need only to be trimmed to encourage dense growth and to limit height. For a formal hedge, you'll need hedge shears. And string and stakes and a level. Trust the experts on this one: If you want a straight, uniform hedge, you must do more than eyeball it. String lines, test with a level, and trust that bubble no matter what your eye tells you.
As with other plants, do maintenance work first—remove damaged and dead wood—then prune your hedge for shape and size. The best time to prune conifer hedges is early spring, before the plants break bud, then again in midsummer. That timing ensures that the cuts you make will be quickly hidden by new growth. Deciduous hedges should be pruned according to the special needs of the plants you're using, especially if you've planted flowering or fruiting species.
Karen Davis Cutler, who has edited five previous BBG handbooks—Essential Tools, Salad Gardens, Tantalizing Tomatoes, Flowering Vines, and Starting from Seed—gardens on 15 acres in northern Vermont. A frequent contributor to national garden magazines, her latest book is The New England Gardener's Book of Lists (2000).