Yellowjackets are unwelcome visitors to picnics and barbecues. Their populations tend to build up during the summer.
These social wasps are particularly attracted to sweet things like soda. Good sanitation -- covering all outdoor drinks and foods and putting food away as soon as possible -- is the best way to minimize problems.
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Yellowjackets tend to make their nests in the ground or in stone walls. You may be able to locate the nest by watching where the wasps fly while you are working in the garden. When the weather is warm during the day, there will be many yellowjackets flying in and out of the nest.
Two other kinds of wasps often found in home landscapes are considered beneficial, because they kill other insects. Bald-faced hornets construct large paper nests in trees and large shrubs. These nests can be as low as head height, so you should be aware as you are working in the garden. Paper wasps will build nests under eaves, signs and fence railings and will sting if disturbed. Since these insects are beneficial, control them only if they pose a safety hazard.
It is time to take cuttings of annuals, such as geraniums and begonias, that are to be kept over the winter. These plants will become more difficult to root once cool nights in September harden them off.
Take a cutting 2 to 3 inches long from the end of a stem, and stick the cut end into a moist, well-drained potting medium, such as one part peat moss and one part perlite.
Keep the cuttings in bright light with moist soil. Cover them with a plastic bag to hold in humidity, but ventilate it daily by opening and resealing the bag.
Once the cuttings are well rooted, typically in 2 to 4 weeks, transplant them to 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.
Do not forget to check the oil and clean out the air filter on your lawn mower on a regular basis. It is easy to overlook this task as you mow throughout the summer, but the engine can be ruined by letting the machine run out of oil.
Keep checking the air filter into the fall. The dust raised when mowing over dry leaves can clog it up, which will impair the performance of the engine.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.