Time to plant cool-season vegetables

Cool-season lettuces, mesclun mixes and other greens that were planted in early spring may be planted again. If the weather is unusually hot, plant these greens in partial shade or wait a few days until there is a cooler forecast.

The best quality and best tasting salad greens come from plants that are watered frequently and lightly rather than infrequently but deeply. This advice is the exact opposite to what is recommended for watering trees, shrubs, perennials, grass and other plants.

• It is time to protect the trunks of smooth-barked trees like young maples from deer. Deer rub their antlers on trees and will typically use the trunks of smooth-barked trees. This can damage the bark and even kill trees if the damage goes all around the trunk. Wrap the trunks with hardware cloth, chicken wire or plastic snow fencing to a height of 5 feet to help protect the tree. This is especially important if you live near a forest preserve where deer are present. This protection can be removed in late winter or early spring.

• Powdery mildew (a disease that causes a grayish, powdery film on leaves) is present now. Commonly affected plants include lilacs, phlox, bee balm, zinnias and nannyberry viburnum. This disease typically occurs in late summer when the weather is warm and humid. Fungicides can help control powdery mildew if applied before the infection becomes severe. In most cases, there is no need to apply any control 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. Nitrogen is the most essential nutrient, but too much nitrogen can cause excessive top growth and disease problems. In most cases, a rate of one pound of nitrogen per 1,000 square feet of lawn is adequate.

Many soils in Chicago area have adequate levels of phosphorus so it is likely not needed for your lawn. Some villages ban the use of phosphorus to help protect water quality, as it can fuel algae growth in lakes and streams.

If you only fertilize your lawn once a year, now is the best time to fertilize.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.