Protect Breakable Pots
Clay and ceramic pots can crack over the winter if left outdoors with soil in them or if they fill with rain. When the water freezes, it expands, and so does wet soil. Empty pots and store upside down under a tarp or bring them in out of the weather.
Check Houseplants for Insects
Plants that summered outdoors may have brought in freeloaders that are now multiplying like crazy in our heated homes. Inspect the undersides of the leaves for webbing of spider mites. Leaf axils (where they attach to the stems) are favorite hiding places of mealybugs. Dark-colored scale insects hug the stems and veins of the leaves and can be invisible unless you look closely. Insecticidal soap is most effective on soft-bodied insects like spider mites, aphids, and mealybugs. Scale is trickier to control and horticultural oil is the best option.
Store Fertilizers and Sprays
Keep insecticide sprays in a place where they won't freeze this winter. Store fertilizers and rock powders in plastic containers so they stay dry and critters don't get into them.
Plant More Bulbs
Take advantage of sales on spring-flowering bulbs and tuck some more in. There's little chance of you thinking come spring, "Gee, I wish I hadn't planted so many bulbs." But steer clear of any that are very small or soft because they won't flower well, if at all.
Cut Back Diseased Perennials
If your bee balm or phlox or any other perennials were covered with powdery mildew last summer, cut the stalks to the ground and dispose of them, ideally by burying them in an out-of-the-way spot. Don't compost them. If roses had black spot, pull off all the leaves and dispose of those, too. Removing the mulch beneath the plants is an important preventative step, too.