If you have a garden pond now is the time to prepare for the ice and snow which arrives with the onset of winter. The most important thing is to make sure that the pond does not become completely covered in ice since this will trap decomposing plant material and other waste and block the normal ventilation from the surface. This article by Margaret Roach which I found on her A Way To Garden website contains some useful tips on the best way to winterize your pond.
IN MORE THAN 20 YEARS of operating two homemade in-ground water gardens, I have probably broken lots of rules—especially about winterizing. But there are some rules I never break, and keeping the surfaces from freezing over is the most important one of all.
If trapped under a solid sheet of ice, decomposing plant material and wastes from fish or other inhabitants can create a building of noxious elements such as ammonia, nitrites and carbon dioxide, all of which can harm (or suffocate) any life overwintering in the pool, and also taint the water.
Make a plan now to keep a hole in the ice; never let the pool freeze completely over. Depending on the pool size and your wintertime lows, maintain at least a small hole in the ice with an appropriate wattage level of floating pond de-icer (that’s one of mine, above; there are many styles and sizes). Water-garden suppliers can help you choose the correct de-icer.
Some water gardeners use a bubbler, or aerator, operated by a pump and submerged maybe 6 inches and positioned near the edge of the pool, to keep a hole open; that doesn’t work here in a harsh winter, but may for you. In early spring, before I pull the de-icer, the frogs act as if it’s a float to sunbathe on (below). All winter long, the birds thank me for supplying water as a side-effect of my de-icing scheme.
See more at A Way To Garden