How and When to Prune Shrubs
While working in the garden this weekend, I noticed at least four of my older shrubs are in dire need of pruning. They’re large and overgrown, and only seem to leaf out on the outside of the bush.
We’ve all seen neighbors and even gardeners take a hedge saw to a shrub, lopping off the top and sides. This technique works for a year, maybe two, before the shrub begins to look like mine.
Below is a summary of when to prune your shrubs and the best techniques to do so.
WHEN TO PRUNE
Pruning at different seasons triggers different responses. Late winter or early spring, before bud break, is usually the best time to prune many species because new tissue forms rapidly. However, pruning should be delayed for most spring-blooming shrubs until immediately after flowering to avoid reducing the floral display.
Summer pruning tends to suppress growth of both suckers and foliage. Summer-blooming shrubs should be pruned in early spring prior to bud set, or in summer immediately following flowering.
Late summer or early fall pruning causes vigorous regrowth, which in some cases may not harden off by winter, leading to possible cold damage. Whenever unexpected damage from vandalism or bad weather occurs, prune at once.
Trees and shrubs that bloom early in the growing season on last year’s growth should be pruned immediately after they finish blooming. Examples of these types of bushes include:
• clove
• currant
• Juneberry
• azalea
• lilac
• chokecherry
• forsythia
• early blooming spirea
Shrubs grown primarily for their foliage rather than showy flowers should be pruned in spring, before growth begins:
• alpine
• currant
• dogwood
• purpleleaf
• sandcherry
• barberry
• honeysuckle
• smokebush
• buffaloberry
• ninebark
• sumac
• burning bush
• peashrub
Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood. Hardier shrubs such as late blooming spireas and smooth (snowball) hydrangeas should be pruned to the first pair of buds above the ground.
PRUNING HEDGES
After the initial pruning at planting, hedges need to be pruned often. Once the hedge reaches the desired height, prune new growth back whenever it grows another 6 to 8 inches. Prune to within 2 inches of the last pruning. Hedges may be pruned twice a year, in spring and again in mid-summer, to keep them dense and attractive. Prune hedges so they’re wider at the base than at the top, to allow all parts to receive sunlight and prevent legginess.
RENEWAL PRUNING FOR OLDER OR OVERGROWN SHRUBS:
Rejuvenation: The first technique involves complete removal of the entire plant 6-10 inches above the ground. Use heavy lopping shears and a pruning saw. Remove half of the new canes that develop by mid- summer, and head back some of the remaining canes. When using a heading cut, be sure to prune to outward-pointing buds so that the inner portion does not become too dense. Shrubs that tolerate extensive rejuvenation are:
• abelia
• dogwood
• honeysuckle
• hydrangea
• lilac
• mallow
• rose-of-Sharon
• spirea
• St. John’s wort (hypericum)
Thinning: The second technique for shrub rejuvenation removes growth more gradually. The first year, remove one-third of the oldest, unproductive branches. The next year, take one-half of the old, lingering stems. Finally, in the third year, prune out the remainder of the old branches. New, productive stems should quickly replace the old wood. This method takes longer to complete, but the shrub stays more attractive throughout the rejuvenation period.
PRUNING EVERGREENS
With few exceptions, evergreens (conifers) require little pruning. Different types of evergreens should be pruned according to their varied growth habits.
Spruces, firs and douglas-firs don’t grow continuously, but can be pruned any time because they have lateral (side) buds that will sprout if the terminal (tip) buds are removed. It’s probably best to prune them in late winter, before growth begins. Some spring pruning, however, is not harmful.
Pines only put on a single flush of tip growth each spring and then stop growing. Prune before these “candles” of new needles become mature. Pines do not have lateral buds, so removing terminal buds will take away new growing points for that branch. Eventually, this will leave dead stubs.
Pines seldom need pruning, but if you want to promote more dense growth, remove up to two-thirds of the length of newly expanded candles. Don’t prune further back than the current year’s growth.
Arborvitae, junipers, yews, and hemlocks grow continuously throughout the growing season. They can be pruned any time through the middle of summer. Even though these plants will tolerate heavy shearing, their natural form is usually most desirable, so prune only to correct growth defects.
USE THE RIGHT TOOLS FOR PRUNING
The right tools make pruning easier and help you do a good job. Keeping tools well-maintained and sharp will improve their performance. There are many tools for pruning, but the following will probably suffice for most applications:
• A good pair of pruning shears is probably one of the most important tools. Cuts up to 3/4 inches in diameter may be made with them.
• Lopping shears are similar to pruning shears, but their long handles provide greater leverage needed to cut branches up to 11/2 inches in diameter.
• Hedge shears are meant only for pruning hedges, nothing else. They usually cut succulent or small stems best.
• Hand saws are very important for cutting branches over 1 inch in diameter. Many types of hand saws are available. Special tri-cut or razor tooth pruning saws cut through larger branches — up to 4 inches in diameter — with ease.
• Pole saws allow for extended reach with a long handle, but they must be used carefully as it’s difficult to achieve clean cuts with them.
• Small chain saws are available for use on larger branches. Operators must wear protective clothing and exercise caution when using them. Never use chain saws to reach above your shoulders, or when you are on a ladder.
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