Take cuttings now to overwinter annuals
This is a good time to take cuttings of annuals that you plan to keep over the winter such as geraniums and begonias. Cool nights in September will harden off the plants, which will make them more difficult to root.
Take a tip cutting 2 to 3 inches long and stick it in a well-drained potting medium such as one part peat moss and one part perlite. Keep the cuttings in humidity and bright light. Cover the cuttings 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 to a 2- to 4-inch pot filled with a growing medium. The size of the new pot should depend on the vigor of the rooted cuttings. Keep the plants in a brightly lit window.
Foliage has suffered this year
I have seen more foliar disease on perennials and trees this year due to the weather. There is not much that gardeners can do other than providing supplemental water during dry periods to help reduce stress on the plants.
A gardener asked me recently whether she should remove a peony with discolored foliage. The peony had been doing well for a few years in this location but appeared to have anthracnose, which is a disease that causes brown spots on the leaves that can merge to form irregular dead areas. It should be healthy going forward, but much will depend on next year’s weather.
Yellowjackets, wasps and hornets
Populations of yellow jackets (a yellow-bodied social wasp) build up in late summer. They are unwelcome visitors to picnics and are particularly attracted to sweet things like soda.
Keeping your patios and decks clean is the best way to minimize problems with yellow jackets as well as other pests. They tend to make their nests in the ground or in stone walls, so watch these areas as you are working in the garden.
When the weather is warm during the day, there can be a lot of activity with yellow jackets flying in and out of their 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.
Mower maintenance
Do not forget to check the oil and clean out the air filter on your lawn mower regularly. It is easy to overlook these basic maintenance tasks as you mow throughout the summer. The engine can be ruined if it runs out of oil. It is a good idea to sharpen your mower blades after about every eight hours of use.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.