The timetable for winterizing your pond depends on how extreme your winter weather is. In the South East or the West Coast, the temperatures rarely dip below freezing long enough to cause problems. For those further north, however, it's a good idea to start before the weather gets extreme. If your pond houses fish, start by transitioning to a cold water fish food once the water temperature dips below 65 degrees. If you don't have a pond thermometer - this is a good time to get one! You'll use it throughout the year to determine your fish feeding regimen. When the water temp dips below 50 degrees, stop feeding altogether. Fish who continue to eat when their metabolism has started to slow down could suffer from a season's worth of indigestion.
Before leaves start dropping, install a pond net to capture leaf litter before it sinks to the bottom of your pond. If late fall rolls around and you still have organic debris on your pond bottom, remove as much as you can - a pond vac is a helpful tool in this case. Remove any aquatic plants that are not hardy for wintering over in your pond. Those are typically annuals and it's fine to compost them - you'll want to buy new in the Spring anyway. Cut back your hardy aquatic plants to the recommended height - 2" above the crown for water lilies, for example. Once they're all cut back, move the lilies to a deep part of the pond. Fish don't need to eat much when the temperature drops, but they do need to breathe. Keep an aeration system going throughout the winter, and if you're in ice skating or hockey territory, add a floating de-icer to the pond to keep an open area for gas exchange.
