Kelly Jackson
Christian County Extension Office
Pruning Out of Control Shrubs
Deciduous shrubs are a key component of a well-designed landscape. Like fertilization and watering, pruning should be considered part of the regular maintenance of shrubs. However, they are frequently pruned incorrectly. Sometimes gardeners view pruning as a yearly ritual that must be done – even if it is not needed. Other times, a plant has to out-grow its space before the decision is made to prune. Maybe one explanation is that people are not confident enough in their pruning skills so shrubs are left to become overgrown. Or maybe gardeners learn incorrect information as they try to copy what they see other misinformed gardeners do to their shrubs. In thisarticle we will look at the basic pruning techniques for shrubs and what to do when your shrubs are out of control.
The first decision to be made is when to prune. For occasional, light pruning the answer is anytime. The best time for removing larger stems is during the dormant season (late winter to early spring, just before bud break). During this time you will put less stress on the shrub and stems will heal faster as they come out of dormancy in the spring. Avoid pruning in late summer or early fall as the resulting tender new growth will be injured by cold weather during the winter. These rules work for flowering or non-flowering shrubs but if your shrubs are spring blooming you could delay pruning to immediately after flowering so you can still enjoy the floral display.
Two techniques are used in maintenance shrub pruning – heading and thinning.Heading is the random cutting of the ends of stems to a bud. Sometimes heading cuts are made with shears. The problem with this method is that thick new growth is produced near the outer portions of the shrub. In time, this reduces sunlight and results in the loss of foliage inside the plant canopy. The plant will also appear stemmy and top-heavy. A better method is to head back stems to several different heights. Stems should be pruned near outward facing buds so the resulting new growth is more open and healthy.
Thinning is a technique whereby stems are cut back to a side stem or the main trunk. This is a much less conspicuous pruning method that results in a smaller, more open plant without causing excessive growth. Thinning doesn’t leave stubs like heading cuts but does create a much fuller, more attractive plant.
In situations where shrubs have over-grown their boundaries, it may be necessary to prune severely. Renewal pruning is best described as a complete removal of all branches to within 6 to 12 inches of the soil. This is a good technique to use on plants that are hiding windows, appear out-of-scale with the house, or have a loss of vigor including reduced flowering. Ideally, we should select shrubs to avoid these problems but sometimes we inherit a landscape already in this condition. Not all shrubs respond favorably to renewal pruning. Most evergreens (i.e., boxwood, junipers, yews) are intolerant and may decline after pruning. Broadleaf shrubs such as abelia, nandina, privet, forsythia, spirea, lilac, and weigela respond well to renewal pruning. The absolute best time for this type of pruning is just before spring growth begins. Renewal pruning is not a cut it andforget it method. By mid-summer your shrub will have a healthy crop of new shoots 12 to 24 inches long. You will need to remove half of the new shoots and prune some of the remaining shoots back to an outward-pointing lateral bud to encourage branching and a more compact shrub. Fertilization, watering, and pest management will be of a bigger concern for renovated shrubs in the immediate years following.
If renewal pruning sounds too drastic, you may try a gradual renewal pruning. This alternative method cuts back all shoots of the shrub over a period of three years. In the first year, one-third of the old, mature stems are removed. In the second year, remove another third of the stems and prune back any long stems from the new growth. In the third year remove the last of the old stems and prune back any long stems from the new growth. This method takes much longer than renewal pruning but the shrub stays more attractive during the pruning process. Red and yellow twig dogwoods and beautyberry respond well to this type of pruning.
Remember not to coat pruning cuts on shrubs with paint or wound dressing. These materials won’t prevent decay or promote wound closure. In the end a good pruning job should not be conspicuous and the plant should be left in better health. Once pruning becomes more familiar and is viewed as part of the annual maintenance of shrubs, it will no longer be a daunting gardening task.