Q. A number of articles have been written about the over-wintering of fish, water lilies and hardy bog plants. However, I have not read any information concerning the over-wintering of oxygenating plants, floating plants or scavengers, such as snails. I have spent a considerable amount of money on these items and would therefore appreciate some helpful information.
A. The amount of effort that is needed to “winterize” a pond depends greatly on where you live and the local climate. For our purposes, let’s assume that winter means that a killing frost will occur sometime between October and December and that water temperatures will drop into the 40s (Fahrenheit) for a month or more. Ice may form over the pond surface for a few weeks to a few months.
Let’s start at the pond’s center — the area in most ponds that is the submergent plant zone — and work our way to the shore. If your pond has submergent plants, such as Cabomba, Elodea or Vallisneria, these plants will winter well underwater as long as the ice does not reach them. At some point in the late fall, it is good practice to trim back these plants to within an inch of the gravel bed or pot. Most likely these plants will die back over winter and there is no need to add decaying organic matter to the chilled waters. This cropping will also stimulate branching in the spring, producing more luxurious growth.
If, however, your pond is so shallow that ice will reach down to these plants, and if the plants are in pots, then it is preferable to remove them from the pond entirely. Trim them back and place them, submerged, in a tub with water that remains at about 40 to 50 degrees Fahrenheit. Do not expose them to light — you do not want to stimulate growth. The following spring all you need do is place them back in the pond after water temperatures reach up into the mid 40s and the threat of ice is gone. If your submergents are rooted in the gravel bed in the pond just leave them alone.
Moving now to the floating leaf zone, the plant most folks worry about is the water lily. Hardy water lilies can remain in the pond over winter as long as a few precautions are taken. After the first frost, cut back the leaf and flower shoots to within an inch of the tuber. The plant is dormant now and these leaves will die off anyway.
Next, it is important to ensure that the lily tuber does not become frozen in ice. If your lily pots are in the shallow end of the pond where ice forms, move them to deeper sections that remain ice free. In the spring they can be returned to their former location.
Lotus and tropical lilies will not over-winter in cold conditions. These plants need to be removed from the pond and stored before the first killing frost.
One procedure that I have had success with is to trim the plants back to the tuber/root stock and store the pot in a dark, cold cellar. The pots should be kept moist and cool, about 40 to 45 degrees Fahrenheit. Dampened cloth or newspaper should be spread over the pot and the whole assembly sealed in a plastic bag. They will remain dormant this way for a few months. This same procedure can also be used for hardy lilies if your pond is too shallow for ice-free submergence. Other folks remove the tubers/root stock from the pot, wrap them in damp newspaper and seal in a plastic bag for winter storage in a cool section of the basement.
Two cautions are in order. First, check the plants frequently to make sure they remain damp. Also, check that molds, mildews or fungi are not beginning to appear.
Second, rodents can be a problem. You may not even know that you have mice in your house until you notice your favorite red water lily tuber has a big chomp taken out of it. In such cases, it is best to store the tubers in sealed trash pails.
Floating plants, such as water hyacinth and water lettuce, will not survive the winter outdoors. These must be brought indoors when water temperatures are still in the 60s. You can try keeping some alive by placing a 10-gallon aquarium in a sunny window. Or, a heated tropical aquarium with strong grow lights makes a nice refuge for these plants. In either case, air and water temperatures should remain in the 70s. I have had only moderate success with over-wintering these plants.
At the emergent zone of a pond we find many bog plants. Hardy bog plants can be treated like hardy lilies. Cut them back and submerge the pots to ice-free depths. If the plants are growing in open gravel beds, don’t worry about them. In fact, all of my pond irises grow “bare root” in the water and are frozen in 18 inches of ice every year. They have come back beautifully each spring.
Tropical bog plants need to be brought indoors. A sunny window and warm location will keep them happy. Alternatively, you can store them in a manner similar to tropical lilies.
Whether or not you have to do something special for your scavengers really depends on the genus and species. For example, the snails in my pond showed up on their own. Because they are locals, they know how to take care of themselves in winter — I ignore them in my winterizing routine.
If you have purchased some of the more exotic tropical and semitropical snails, then you have little choice in the matter. You can either let them die outdoors or bring them in for the winter. The latter option means setting up a tropical tank with plants, adequate lighting, good filtration and so on, just like any home aquarium. The biological filter must be fully functioning before the animals are introduced to the tank.
Moving snails or any aquatic animal or plant is just like moving fish. Be sure to match pH and water temperature between the pond and the tank. The water must be chlorine free and well aerated. In fact, it is always preferable to fill the aquarium with pond water right before the move so that water quality is matched exactly. Then, over several days, the water can be changed using partial water changes.