Q. I have a small garden pond that holds about 1000 gallons. It is a liner pond and has a natural gravel bottom. My water plants are rooted in the gravel without pots. Each autumn, leaves from the trees fall into the pond and settle on the bottom. My question is: Do I have to clean out the leaves? I understand that when the pond ices over, decay gases can build up and kill fish. I keep three pool comets in the pond and I do not want anything to happen to them. But at the same time, cleaning out the leaves will uproot my plants and create a mess.
A. The short answer is: no. If you only have several comets, they will be fine. I do believe, however, that it is good practice to remove as much of the leaf matter as possible before it sinks to the bottom.
When leaves hit the water they begin to release many substances into it. Tannins, for example, color the water brownish orange (similar to a strong tea). Phosphorus is also released, which will feed algae next spring. This substance release begins immediately and proceeds rapidly. Moreover, some leaves such as oak and pine needles will acidify the water as they decompose.
It therefore makes sense to skim the pond as soon as the leaves start to accumulate on the surface. This takes much less time than most pondkeepers imagine. (Many maintenance chores seem to take hours, when they really require just a few minutes.)
To the extent that it is possible and convenient, without disrupting the pond bottom or plants, remove leaves on the surface of the water. You certainly do not want the pond floor buried in 2 feet of leaves. But it is also true that decayed leaf matter will enrich the gravel bed of your pond.
You will notice that as winter approaches the comets actually burrow into the leaf matter. Obviously, it does not bother them and they seem immune from the hydrogen sulfide that is generated. In fact, most instances of fish deaths under the ice are caused by too little oxygen, too much carbon dioxide or both.