Apply fertilizer to your lawn early this month, then again mid-to-late October, for a thicker, healthier lawn next spring. Sweep up any granules that land on walks or driveways, to keep them from making their way into storm sewers and, ultimately, lakes and rivers.
Core aerate your soil just prior to fertilizing, if it is hard and compacted. Allow soil cores to sit atop the grass where they'll crumble and "topdress" your lawn, reducing thatch buildup.
This is an excellent time to add evergreen trees and shrubs to your landscape. Lengthening nights, cooler temperatures, and increasing rainfall create favorable transplanting conditions. And many nurseries have sales to clear their stock this time of year.
Bring all houseplants indoors except Christmas cactus and florist's azaleas. Keep them outdoors until night temperatures drop to the high 30s. Cold nights help trigger flower formation; buds should develop shortly after the plants return indoors.
Seal up cracks and spaces in your home's foundation and remove leaves, mulch, and other plant debris nearby to deter millipedes, sowbugs, and spiders that may try to enter from outdoors as weather grows cooler.