As fall approaches, it is time to protect the trunks of smooth-barked trees such as young maples from deer rubbing. Deer rub their antlers on trees, typically those with smooth bark. This can damage the bark and even kill trees if the damage goes all around the trunk. Wrap the trunks with tree wrap, chicken wire or plastic snow fencing to a height of 5 feet to help protect the tree. Remove this protection in early spring.
Crab grass may be evident in your lawn now. This annual weedy grass seeds readily in the fall. Keep crab grass closely cut to prevent it from forming seeds or pull it out by hand. Some herbicides can control crab grass but will not be as effective after the weed has set seed. Make note now of bad areas in your lawn so you can apply a pre-emergent herbicide (one that prevents weed seeds from germinating) in early spring, before lilacs flower.
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Powdery mildew (a fungal disease that causes a grayish, powdery film on leaves) is present now. Common plants that can get powdery mildew include lilacs, phlox, bee balm, zinnias and nannyberry viburnum. This disease typically occurs in the late summer when the weather is warm and humid. Fungicides can help control powdery mildew, but only if applied before the infection becomes severe. In most cases there is no need to apply any controls for powdery mildew at this time of year. Other options include selecting more mildew-resistant varieties or moving the infected plants to an area of the garden that has better air circulation.
Fertilize your lawn in early September to improve the color and vigor of the grass. If you only fertilize your lawn once a year, this is the best time to do it. The nutrient grass needs in the greatest quantity is nitrogen, although too much nitrogen can cause excessive top growth and disease problems. In most cases a rate of 1 pound of nitrogen per 1,000 square feet of lawn is adequate. Soils in the Chicago area tend to have adequate levels of phosphorus, so this nutrient is likely not needed for your lawn. Since phosphorus can fuel the growth of algae in lakes and streams, some municipalities ban its use in lawn fertilizer.
It is time to order spring-flowering bulbs. When planning your bulb garden, choose a site with well-drained soil. Any area in the garden that remains wet for long periods or has standing water for any length of time is unsuitable for bulbs.
They prefer moisture in spring and fall and drought in summer. Leucojum aestivum, summer snowflake, does have some tolerance to moist conditions. Most spring-flowering bulbs prefer full sun. When planted beneath a tree with high branches, spring bulbs will often flower in the sun that reaches them before the tree leafs out.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.