PLANTING AND MAINTAINING HEDGES
In Pacific Northwest Gardens
by Joëlle Steele
For centuries, gardeners have been using hedges to create walls, to section off areas, to screen unwanted views, to direct foot traffic, and for purely ornamental reasons. By carefully training plants when they are still very small, gardeners have managed to grow healthy, well-formed, and sometimes massive hedges. Today's gardeners are not always as fastidious in their growing methods as their earliest predecessors. As a result, many hedges are grown from the wrong kind of plants, are poorly developed, and badly maintained. In the end, it's nothing more than a slow and certain death for the hedge.
SELECTING HEDGE PLANTS
Always select plants that will not outgrow your ability to maintain them. For example, if you only want a 4' hedge, don't buy a fast-growing plant that has the ability to reach 20' in height. You will spend way too much time pruning it.
The following are a few plants that grow well as hedges in the Pacific Northwest. Check with your local nursery to make sure that the ones you plan to buy will grow in your zone and that they grow to a height and spread that meets your needs.
Buxus spp. ("boxwood") (slow growing)
Cupressocyparis leylandii (fast growing)
Escallonia spp. (fast growing)
Ilex crenata ("Japanese holly")
Lonicera nitida ("boxleaf honeysuckle") (fast growing)
Myrica californica ("Pacific wax myrtle")
Nandina spp. ("heavenly bamboo") (slow growing, not a real bamboo)
Osmanthus delavayi (slow growing)
Photinia spp. (fast growing)
Prunus laurocerasus ("English laurel") (very fast growing)
Rhamnus cathartica ("common buckthorn") (fast growing, can be invasive)
Taxus spp. ("yew")
Thuja spp. ("arborvitae," "cedar," "western red cedar") (slow growing)
Tsuga canadensis ("Canada hemlock")
PLANTING AND TRAINING
To have a healthy and successful hedge, you have to be very, very patient — a lesson most gardeners learn early on with all growing things. Even the fastest-growing shrubs will take at least four or five years of training to grow into a strong hedge.
Start with plants that are only about a foot or two in height, and try to find ones that have lots of branches because, immediately after you plant them, you will have to cut them down to about one-fourth of that height, or down to roughly 8"-10" in height. Cutting them back so severely forces them to branch further at what will ultimately be the bottom of your hedge, which establishes a good basis for future healthy growth.
A few months later or just before new leaves start to bud in spring, you'll have to cut back one-half of their new growth. And a year after that, just before spring budding, cut off one-half of the new growth again.
SHAPING YOUR HEDGE
By the time your hedge is three or four years old, the plants should be growing together, and that is when you will need to start pruning them into an attractive shape. Always resist the urge to "box" your hedge. It seems like the easy way to trim a hedge, but flat-shearing it on the sides and top destroys the natural form of the plant and creates unhealthy plants as well. If your hedge is a flowering species, you will sacrifice the majority of its flowers by such extreme pruning. Letting your hedge plants grow into their natural shape also prevents them from accumulating snow that they cannot shed quickly, which may damage the leaves and branches.
The optimum form in which to shape a hedge is a natural one, and while this varies from one plant species to another, it is generally a form in which the center top of each plant is either slightly rounded or pointed, and the lower part of the plant is slightly wider than the top. To start your hedge off in this direction, begin by pruning the top a bit narrower than the bottom. This will allow all the leaves of the plant to get the same amount of sunlight, and this prevents your hedge from turning into a very big collection of sticks with just a few leaves showing at the tips.
PRUNING YOUR HEDGE
Use hand-held pruners, not power shears. Hand-pruning your hedge will result in a pretty, healthy hedge. It takes longer to hand-prune, but when a hedge is allowed to grow in a natural form it doesn't require the frequent pruning that a boxed hedge does. You can hand-prune once or twice a year, more frequently for fast-growing varieties.
For evergreen hedges, prune when the plant is dormant and before it produces leaf or flower buds. The best time for this is usually late winter to early spring, after the snow and freezing temperatures are past. If you have a flowering hedge, prune it right after it is finished flowering. Never prune your hedge — or any other plant or tree — when it is either in the process of producing leaves (in the spring) or losing leaves (in the fall). If you must prune in summer, do so later in the season after flowering is over.
If possible, try not to let the new growth on your hedge plants exceed one foot before you trim them back. If you have a fast-growing hedge and want it to grow taller, prune it more frequently and remove less new growth each time you prune. If the hedge has reached it maximum height and you just want to keep it neatly manicured, prune back the new growth as it grows in.
FIXING AN OLD HEDGE
If you have an old hedge that has been badly shaped and pruned, you may still be able to salvage it. But, it won't take you any less time than if you planted an entire new hedge and went through the four or five years it takes to get it to the size and shape you want. When a hedge has been let go for five years, it will probably take at least three years to get it back in shape, if at all.
To fix an old hedge, wait until spring, just before leaf buds appear, and prune it down about 8"-12" shorter than the maximum height you want it to be. Then watch it as it grows and keep it carefully pruned and trimmed. If the hedge is in such poor condition that it cannot be grown back, you will probably have to replace the hedge entirely.
This article last updated: 02/21/2013.