Pruning back shrubs and trees gets you out in the yard
Winter is a good time to prune trees and shrubs. Overgrown deciduous woody shrubs can be rejuvenated with heavy pruning this month and continuing until new growth begins in spring.
Start by removing all dead wood. Prune old canes off at ground level whenever possible, leaving young canes that are smaller in diameter. Try not to leave stubs at the base. You may need to cut back the remaining young stems if they are spindly and flop over.
If there are not any young canes, cut the large canes back to 2 to 3 feet from the ground. This will be unsightly, but if the plants are healthy, extensive new growth should start from the old canes in spring and fill in the plant. Shrubs such as lilacs that formed flower buds last summer will not bloom this year if they are pruned aggressively in winter.
Some of the stems will die back when the plants begin growing, so prune the dead wood out as needed in summer after giving the shrub plenty of time to grow out.
• Water any evergreens planted in containers outside during any warm spells that occur throughout the winter. Evergreens continue to lose water through their leaves and will be more likely to suffer winter burn if they dry out in the containers.
• Continue cutting buckthorn out of native habitats or garden areas during the winter. There will be less impact on herbaceous native plants or adjacent perennials borders when this work is done on frozen ground.
Be sure to treat stumps with an herbicide such as glyphosate or triclopyr to kill the root system. Glyphosate needs to be used at a high enough concentration to work as a stump treatment. Some recommend a 50% concentration, but our Chicago Botanic Garden staff has had success with a lower concentration of around 30%.
One of the drawbacks with glyphosate is that it is water-based and will freeze when temperatures are cold enough. It is also only effective on the cut surface.
Triclopyr is the preferred method because it is oil-based, is effective through the bark and on the cut surface and will not freeze. Treat the cut stumps promptly after cutting for best results.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.