How to overwinter annuals, avoid wasp stings and train espaliers
It is time to take cuttings of annuals such as geraniums and begonias that you want to keep over the winter. Cool nights in September will harden off the plants, which will make them more difficult to root.
Take a 2- to 3-inch-long tip cutting and stick it in a well-drained potting medium for container gardening. Keep the cuttings in humidity and bright light. Cover them with a plastic bag and ventilate daily by opening and resealing the bag.
Once they are well rooted, typically in two to four weeks, transplant them into a 2- to-4-inch pot filled with a growing medium. The size of the new pot will depend on the vigor of the rooted cuttings; use a larger pot for a more vigorously growing plant. It’s OK to grow the plants outside until temperatures start dropping below 50 degrees.
Wasp warning
I have been stung a few times by yellowjackets while gardening, so I’ve learned to be more aware at this time of year. The populations of yellowjackets (yellow-bodied social wasps) build up in summer. They are unwelcome visitors to picnics and are particularly attracted to sweet things like soda.
Practicing good sanitation is the best way to minimize pest problems. The wasps tend to make their nests in the ground or in stone walls, so watch these areas as you are working in the garden. Yellowjackets are active when the weather is warm during the day, flying in and out of the nest.
Bald-faced hornets construct large paper nests in trees and large shrubs at head height and above, so be aware as you are working in the garden. Paper wasps build nests under eaves, signs and fence railings and will sting if disturbed. These are beneficial insects, so control them only if they pose a safety hazard.
Espalier training
Espalier plants can soften large blank spaces on walls or fences when there is minimal bed space. To train espaliers, bend young supple twigs and branches to meet design requirements. Carefully tie the branches in place with raffia or plastic tape. The ties should be secured loosely so the flow of water and nutrients through the tree’s stems is not constricted. Adjust ties during the growing season as necessary.
Formal espaliers need regular attention to keep them looking good. Plan to prune them several times over the course of the summer.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.