By Dr.James R. Feucht, Colorado State University Cooperative Extension specialist, landscape plants
The fall of autumn leaves and the first snow may mean the end of the gardening season for most, but once the snow has melted, smart folks will latch onto the pruning shears and use this time to correct some shrub and tree problems.
Mid-to-late fall is a great time to prune. With leaves gone, you can see what you are doing and determine where corrective pruning is needed.
Corrective pruning means removing parts of the plant that aren't growing as we'd like. These may be branches that interfere with other branches, those that rub against the house or branches that overhang a walkway or roof. You can decide which ones to remove, but examine the plant carefully first to visualize how it will look after you've finished.
You'll also want to prune to remove dead or broken branches or those with heavy disease or insect infestations. Oystershell scale in lilac, for example, can be diminished by pruning. Scale often is heaviest on the older canes, so by removing them in the fall or winter, you go a long way in controlling scale buildup the following season. By pruning, you may reduce the need to apply pesticides, and you'll be thinning the shrub to allow more light penetration. The result will be a healthier plant.
You also can prune large, overgrown shrubs during fall and winter. Thin them, however, rather than shearing them at the top. Thinning will reduce the plant's size without affecting its overall shape.
Thinning is especially important for flowering shrubs. You can remove some stalks or branches without significantly reducing spring flowering. Plants such as lilac and forsythia, as well as flowering trees, already have formed their flowers for next year. These flowers are tightly encased in buds that, often, are near the tip of the plant. Shearing such plants will reduce, if not destroy, next year's bloom. That's why you should remove only dead, dying or interfering branches at this time of year. To reduce height, cut some major canes completely without pruning the remainder of the plant.
You can prune trees now to make them structurally more sound and less prone to future storm damage. Branches that form narrow "V" crotches are weaker than those with wide-angle crotches. Where possible these narrow "V" branches should be removed. Make the cut just outside the natural "collar." This "collar" usually is marked by wrinkles or a series of ridges in the bark near the branch union. Do not cut flush with the trunk.
If removal of a "V" crotch will destroy the shape of the tree, you can leave it in and add artificial support, using cables and hooks. This is a permanent installation. The cables are attached to screw-eye hooks placed directly through the bark of the tree at a point at least two-thirds the distance between the crotch and the top of the branch that needs support. A similar hook is placed on the main trunk at such a point that will provide a strong support when a cable is stretch between the two hooks. The hooks will not harm the tree. Rather the tree, eventually, will grow around the hooks and they will become buried in the bark. If yours is a major pruning and cabling job, however, it may be a good idea to consult a commercial arborist.
This is a good time to prune back the tops of your perennials and summer-flowering shrubs and roses. Don't prune the latter too severely.You can remove dead flowers and the upper one-third of the canes, just enough to make them look better during winter and prevent them from breaking under the weight of a heavy snow.
Photos: Judy Sedbrook and Lynne Conroy
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010