If you already have a garden pond, clear out any fallen leaves or other debris and cut back withered foliage of water plants. Decaying vegetable matter can upset the delicate balance of the watery ecosystem. Don't do this on a really cold day when the fish are in deep hibernation at the bottom of the pool. New water plants (or fish) should not be introduced until next spring, but if the soil around the edge is fairly dry you can do a bit of pondside planting. The best effect is gained by limiting the range of plants so as not to detract from the drama of the water. Where the pool is self-contained in a liner or plastic form, you can chose types that mimic the look of water-loving, marginal plants. Plant swathes of large-leaved varieties like hosta, bergenia and arum lily and strap-leaved plants such as bamboo, Miscanthus, Crocosmia, Dierama and iris.