Plants that prefer acidic soil conditions such as rhododendrons and azaleas can benefit from an application of granular sulfur to the soil in fall. If the blooms of your hydrangeas have turned from blue to pink, sulfur applications may bring back the blue.
Avoid contact with the sulfur by wearing latex gloves and keeping dust out of your eyes. Apply the chemical to the soil and gently scratch it in. Since sulfur works slowly in the soil, repeated applications may be necessary from year to year.
Autumn is a good time to core aerate your lawn to relieve soil compaction and reduce thatch if you did not aerate in spring.
The procedure removes cores of soil, leaving small holes every few inches all over the lawn that allow air and water to reach the grass plants' roots. Core aerating once a year is enough for most residential lawns with normal use. Very high use lawns will benefit from being aerated twice a year.
You can rent a machine to aerate a lawn or hire a lawn service to do the job. Mark sprinkler heads and light fixtures in the lawn so they will not be damaged.
Core aerating is best done when the ground is somewhat moist. Leave the plugs of grass and soil on the grass, where they will be broken down by soil microorganisms and the nutrients they contain will filter back down to the soil level. The plugs typically break down in seven to 14 days.
Aerating also provides an opportunity for overseeding to help improve and thicken up your lawn. After you scatter the seed, keep it moist for good germination.
Among spring-blooming bulbs, Allium or ornamental onions are among the most resistant to animal browsing. They come in many varieties, blooming between late spring and midsummer. Try the popular June-blooming Globemaster, with a 10-inch pinkish-purple flower cluster on a 2- to 3-foot stem; the bloom lasts up to a month. The drumstick onion, Allium sphaerocephalon, has reliable burgundy blossoms about 1-inch wide. Allium moly, lily leek, is a small species that is 10 to 14 inches tall with yellow flowers.
These are just a few of the many alliums that succeed with little effort in Midwest gardens if planted in fall.
Daffodils also are easy to grow and are resistant to animal browsing, while tulips and crocuses are readily eaten.
Continue to harvest vegetables as they ripen. Warm-season crops such as peppers and tomatoes should be picked as soon as possible, but full-sized pumpkins need to remain on the vine as long as possible to achieve their maximum size.
Keep snipping herbs to use fresh, to dry, or to freeze. Try making some extra pesto and freezing it an ice cube tray. Pop out the cubes when frozen and store in a plastic bag for use this winter.
Collards, kale and Brussels sprouts will taste better if they are allowed to be hit with frost before harvesting.
Maintain good sanitation throughout the vegetable garden. Remove diseased plants immediately as well as those that have finished their growth cycle for the year. It is best to compost only healthy plant material. Put leaves and stalks that have been touched by disease in the landscape waste.
Divide perennials that bloomed in spring and summer as needed. It is best to do this early in the month so plants have time to establish before winter sets in. Mulch the newly planted divisions.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.