Fall lawn care: Combating crabgrass, protecting trees, ordering bulbs

This summer, it seems there has been more crabgrass than usual in lawns, even in more established areas of lawns. This annual weedy grass seeds readily in the fall and colonizes bare areas in the lawn while thriving in hot weather.

Keep crabgrass closely cut to prevent seed formation or pull it out by hand. There are herbicides that control crabgrass, but they are not as effective once the crabgrass has formed seed. I used an herbicide called Q4 plus at home this year. Make note of bad areas in your lawn and apply a preemergent herbicide (one that prevents weed seeds from germinating) in early spring if you have a large infestation of crabgrass. The herbicide must be applied before crabgrass begins to germinate.

Fertilize your lawn in September to improve the color and vigor of the grass. Nitrogen is the most essential nutrient, 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.

Many soils in the Chicago area have adequate levels of phosphorus, so it is probably unnecessary for your lawn. Some villages focus on water quality and ban the use of phosphorus, 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.

This season is also the right time to protect the trunks of smooth-barked trees like young maples from deer rubs up to a height of about 6 feet. Deer rub their antlers on trees to remove velvet and mark territory. They usually choose the trunks of smooth-barked trees. This can damage the bark and even kill trees if the damage goes all around the trunk.

Wrap tree trunks with a sturdy hardware wire mesh or plastic snow fencing, and use zip ties to secure the wire mesh. This protection can be removed in December, or you can wait until spring. Paper tree wrap and burlap do not provide enough protection from deer rubbing.

Once back-to-school season arrives and the temperatures begin to change in the Chicago area, I like to order spring-flowering bulbs. Order enough bulbs to make an impact once you’ve scouted your garden and chosen 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. Most prefer full sun.

When planted beneath a high-branching tree, early-flowering spring bulbs generally flower before the tree leafs out when they have only light shade to contend with as their foliage matures. Summer snowflake (Leucojum aestivum) does have some tolerance to moist soil conditions.

Tulips and crocuses are favorites of deer and rabbits, so I avoid planting them. I have also had issues with squirrels and chipmunks digging up crocus bulbs in the fall. Daffodils and ornamental onions are good choices, especially if there are animals in the area.

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