Fall is a great time to plant and transplant trees and shrubs. Conditions in autumn, which include warm soil, moderate air temperatures and rain, help plants re-establish their root systems.
Evergreens benefit from planting early in the fall so they have plenty of time to get established, minimizing the chance of winter burn from being too dry. Try to get them planted before the middle of October and continue watering them weekly or as needed until the ground is frozen. They should not go into winter under stress.
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It is important to mulch fall plantings. Use 2 to 3 inches of mulch for trees and shrubs and 1 to 2 inches for perennials and groundcovers, spreading it in an even layer. It is best to keep the mulch a few inches away from the crown of a perennial, the base of a shrub or the trunk of a tree. Mulch that is against the plant's tissues can trap moisture or harbor insects or disease.
In general, trees and shrubs do not need to be pruned when they are transplanted.
Good soil preparation is important for a successful planting. It is best to amend the entire planting area or bed when planting perennials rather than placing amendments in individual holes. Evenly incorporate 2 to 3 inches of compost into the existing garden soil.
Peonies are dependable, long-lived, hardy perennials. After their large, showy late-spring blooms, their neat foliage stays green from spring until frost. They do best in full sun. They can tolerate partial shade, but flowering is reduced.
September is a good time to plant peonies as well as to divide and transplant existing ones. Lift roots carefully from the soil and use a clean, sharp tool to cut the large, fleshy root clumps into smaller pieces. Be careful not to make these pieces too small; each section should have at least three reddish growing buds or "eyes." Plant the divisions with the eyes an inch or two below soil level.
It is time to start thinking about the indoor herb garden. Before frost, carefully lift and pot small herb plants or large perennials such as rosemary or lemon verbena to bring inside.
After potting them, you may want to keep them outside for a few days in a partially shaded spot with even moisture. This will help them adjust to a move indoors. The shock from moving plants from outside to inside can cause some yellowing of leaves. Once inside, keep the herbs in a sunny window.
Be aware of the weather if you spray to control weeds in the fall. Herbicides are most effective when temperatures are consistently above 55 degrees and weeds are actively growing. A still day with no wind will reduce the chance that the spray will be blown to damage other plants. Spot-spray the weeds to minimize the amount of herbicide that you use.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.