Ask the Master Gardener: To prune or not to prune, plus tips for handling aphids
The Springfield News-Leader in Springfield, Missouri, partners with the Master Gardeners of Green County each week to bring readers a question-and-answer column with some of the expert horticulturists in the region.
Colleges and universities in the U.S. typically offer Master Gardener programs, which provide "intensive horticultural training," according to the American Horticultural Society. The certified Master Gardeners then volunteer as lecturers, researchers and gardeners in their communities. For more information about Master Gardener programs in your community, the American Horticultural Society created this page with local resources.
Here's a sample of some of the recent questions amateur gardeners had for the masters of the craft.
Someone recently told me that a woody shrub should never be pruned of old wood because it could die. Is this true? I have a viburnum in need of pruning.
That's a new one to me! This is not true, but I wonder where that person got that information. Pruning old wood, if done correctly, will not harm your shrub. Older shrubs will benefit from pruning of old wood and will stimulate new growth to provide next season's blossoms. Pruning helps shape a shrub, also opening up the interior structure by removing branches that are crossing each other.
Your viburnum should ideally be pruned after it has finished blooming, since it is a spring blooming shrub. The general rule on when to prune blooming shrubs is to prune spring bloomers right after blooming since they bloom on old wood. Fall blooming shrubs should be pruned in very early spring because they bloom on new wood. If a shrub is pruned at the wrong time, you may lose some blooms the next season, but the plant itself will not be harmed. Ideally, a shrub should be pruned by about one-third, some of the oldest sections could even be pruned down to the ground.
What can I do about aphids on my arborvitae? They are absolutely covered and not doing well.
While distressing and unattractive, aphids seldom kill a plant outright, however they do reduce a plant's vigor and may stunt a plant's growth. There are various things that can be done to control these little sap-sucking pests. I prefer to try the least harmful and toxic solutions first, leaving the chemical solutions for more serious infestations. My preference is to wait for natural predators such as ladybugs and parasitic wasps to show up and take care of the problem for you. Certain cultural practices are useful including a brisk spray of water which will remove the aphids. Chemical solution should only be used as a last resort and only on the plants with the worst infestations. When using pesticides, make sure the label specifically mentions aphids and the plant you are treating. The least harmful chemicals, such as insecticidal soaps or pyrethrins, should be used first.
Readers can pose questions or get more information by calling 417-874-2963 and talking to one of the trained volunteers staffing the Master Gardener Hotline at the University of Missouri Extension Center in Greene County located inside the Botanical Center, 2400 S. Scenic Ave., Springfield, MO 65807.