December’s the month for getting your pond into tip-top condition for the spring. By now, most of the marginal plants and bog plants will have started to die down; to prevent these falling into the water, rotting and polluting it, they should be cut back and all the debris removed and composted. Also, remove dead water lily leaves completely, and those of other aquatic plants, and skim off regularly any dead leaves and other bits and pieces that might have blown into it during those periods of strong winds most of us have endured recently. At this time of year, it’s important to keep the water as clean as possible, particularly if you have fish in there. Winter is a time when you might lose one or two less robust fish – keep a close watch on the pond and remove immediately any dead ones floating on the surface.
Remove your pump, if you have one, and give it a good clean and service. This can be put away until the spring, although many manufacturers and pond experts now recommend that it should be replaced and kept running throughout the year, as this is thought to be better for the pump mechanism, and a fountain or other moving water feature helps to oxygenate the water, which is as important at this time of year as it is in the summer.
Take the opportunity of a mild spell to check for leaks, and repair any you might find. Minor leaks might not show during wet spells, but the surface will quickly and noticeably drop at this time of year, when there is little evaporation, if there is a major leak.
Any repair will usually entail removing any fish and pumping out the water to the level of the suspected problem. A very badly leaking pond is best emptied and relined entirely; your aquatic plants will not suffer by being removed for a short time, but don’t split them until they start into growth in the spring or the roots may rot once they are replaced.
The most important thing in winter is to keep at least one area in the pond free from ice. Toxic gases from any rotting organic material near the bottom will build up as they cannot escape; fish and other wildlife can become starved of oxygen in a pond, particularly a small one, which is totally iced up, and will often not survive. In addition, a concrete pond may crack towards the top because of the pressure the expanding ice places on the sides. Many birds rely on your pond for bathing and drinking, so even if you have no fish, it is essential to keep some shallow, open water for them at all times.
The one thing you must not do is break thick ice with a hammer or any other heavy instrument, particularly where there are fish, which will often die from the shock. The most effective way of keeping a section free is to heat water in a large pan and place it on the ice. The warm base will quickly thaw thin ice; repeat this as many times as necessary to clear a reasonable section of the surface. Even if the surface re-freezes, the ice will be thinner here than that surrounding it and is easily cleared again.
A fine spell in December will give you the opportunity to construct a new pond if your garden is lacking one at present. Dig the hole and line it, then fill with water. Your new feature will settle down during the rest of winter, ready for introducing plants and fish when the water starts to warm up in spring. You will have about four months to think about the plants and other items you want so everything should be in perfect order by next summer.