Avoid Overwatering Houseplants
Houseplants will start slowing down their growth now that the days are shorter and light is less intense. Check soil moisture before watering and water only if the soil is dry, and don't fertilize again until early spring. Overwatering and fertilizing when the plant isn't in active growth can damage the roots.
Water Trees and Shrubs
Keep watering newly planted trees and shrubs -- especially evergreens -- into early winter if nature doesn't provide regular good soakings. You want them to enter winter with a good supply of moisture because once the ground freezes, they won't get any more until the ground thaws in spring.
Mark Location of Perennials
Mark the location of your perennials with permanent plant labels now, so you'll know where they are next spring when you start planting. Some perennials, such as hosta, are late to emerge so it's easy to forget where they are and inadvertently damage the crowns and young shoots.
Mow over leaves that have fallen in your yard or, if there are just too many of them, rake them up and compost them. They contain the nutrients that the trees accumulated over the summer, so take advantage of that and let those nutrients return to the soil.
Landscape to Conserve Heat
Heating your home in winter is a big expense, so look to landscaping to help you out. Strategically placed evergreen trees and shrubs can block the wind and provide a buffer between you and the weather. Think ahead to summer, too, and plant shade trees to block summer sun, reducing air conditioning bills.