Core aeration is advised once a year

Autumn is a good time to core aerate and thatch your lawn to reduce soil compaction if you did not aerate in the spring.

Core aerating once a year is enough for most residential lawns with normal use. Very high-use lawns benefit from being aerated twice a year. Aeration and thatching also provide an opportunity for overseeding to help improve and thicken your lawn.

Keep the seed moist for good germination. Core aerating is best done when the ground is somewhat moist. Leave the soil/grass plugs on the lawn to break up and filter back down to the soil level. The plugs typically break down in seven to 14 days.

Mark sprinkler heads and light fixtures in the lawn so they will not be damaged.

• Many lawns that have not been irrigated are looking stressed now, but should recover as the weather cools down and fall rains arrive. Lawns infested with bent grass may have sections that have completely died out, as this grass is prone to disease and tends to die out in late summer.

You will need to reseed dead zones this fall. Lots of small holes dug by raccoons and skunks indicate grub damage, so check just below the surface of the soil for the grubs.

If treating your lawn for grubs is necessary, be sure you use the right product that will kill grubs within 24 hours after being watered in.

• Plants that prefer acidic soil conditions like rhododendrons and azaleas benefit from an application of granular sulfur to the soil in fall. If your blue hydrangeas have turned pink, sulfur applications may return the flower color to blue.

Avoid contact with the sulfur by wearing latex gloves and keeping dust out of your eyes. Apply to the soil at a rate of 2 pounds of sulfur per 100 square feet and gently scratch in. Sulfur works slowly in the soil and repeated applications in spring and fall may be necessary from year to year to get results.

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