JeffCo Master Gardeners: Fall Pruning “Dos and Don’ts” by Audrey Stokes

Sunday, October 2, 2016

Fall Pruning “Dos and Don’ts” by Audrey Stokes

Mild fall weather may have you thinking about pruning shrubs and trees but it's better to wait until winter or at least until after deciduous trees’ leaves have fallen. When it comes to fall pruning, procrastination is the way to go. One exception to any ‘no-pruning’ advice is that dead, diseased and damaged wood should be removed as soon as possible. Hire a professional arborist to remove big limbs, high branches, and any other tree job that you’re not prepared to do.

Pruning timetables can be broken down according to the type of plant: trees, shrubs, perennials and roses.

Trees

In early fall, pruning wounds close more slowly and plants are more at risk for fungal diseases than at other times of year. For most trees, the best time for major pruning is winter to early spring because wounds close faster.
Pruning in late summer and early fall may stimulate new growth, which has little time to harden before cold weather comes. The cold can harm this tender new growth, and the tree may need more pruning in spring to remove the damage.
If you want to prune in fall, wait until trees drop their leaves and are dormant—usually late October or November. “With leaves gone, you can see what you are doing and determine where corrective pruning is needed”, says Dr. James Feucht of Colorado State University Cooperative Extension. (http://www.colostate.edu/Dept/CoopExt/4DMG/Trees/fallprun.htm)
See this CSU Extension video about pruning trees: http://www.youtube.com/watch?v=G7IdsEJCHdg

Shrubs

Shrubs need some pruning every few years. Pruning promotes a more open plant with abundant flowering. Yearly pruning of some flowering shrubs promotes more flowers.
Spring blooming shrubs like lilac (Syringa, various species) and forsythia (Forsythia, suspensa) should be pruned just after blooming in late spring. Pruning later in the season will result in the loss of flower buds for the next year, so fall pruning must be avoided.
Shrubs that bloom later in the summer, such as blue-mist spirea (Caryoptersis x clandonensis) and hydrangea (Hydrangea, various species) should be pruned in late winter/early spring. These shrubs bloom from the current year's growth which begins in early spring.
You can prune large, overgrown (non-spring blooming) 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. You should remove only dead, dying or interfering branches at this time of year.
Shearing is faster than hand pruning and gives a very formal appearance. However, shearing can lead to plant health problems. In leafy shrubs, shearing results in weak and unnatural growth. In evergreens, shearing can enhance spider mite and aphid infestations. Do not shear evergreens in the late fall or winter. The foliage will brown because of water loss from drying winds.

Roses

Pruning roses (Rosa, various species) in the fall is not recommended because the wound created by the cut can result in additional or more severe winterkill of the cane. It is best to leave the roses alone in the fall. Pruning of roses is best accomplished in mid-April after the chance of all hard late freezes is past.
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.
See this CSU Extension video about pruning roses: http://www.youtube.com/watch?v=w5plEPH7pGI
The Denver Rose Society is an extremely good source of information on rose care (http://www.denverrosesociety.org/education/Trepidation_Of_Pruning.pdf).

Perennials

Care and pruning of perennials is very plant-specific and most direction will come from researching the plant itself. Most of the literature on perennials points to avoid fall pruning. Following are a few examples:

Mums (Chrysanthemum, various species) – the pruning of mums should have been done before July. Do not prune after they flower as this will improve their overwintering survival rate.

Basket-of-gold (Aurinia saxatilis) and bugleweed (Lycopus virginicus) - do not cut back for the winter as these species are evergreen or semi-evergreen.

Butterfly weed (Asclepias tuberosa) - allow some of the second bloom to mature into the ornamental fruit for interest. Do not prune for winter, cut back in the spring.
Plantain-lily (Hosta, various species) - leaving foliage on hostas over the winter provides added protection.