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How do I overwinter water garden plants?
You have enjoyed your water garden all summer, and now as the temperature drops and the days shorten, the focus becomes what to do with all those wonderful plants you have installed and cared for. Can they be handled in such a way as to be usable again next year and for years to come? The answer in many cases is yes.
Success with plants that reappear in the spring starts with the selection process. The task of overwintering water garden plants is simplified if you use as many species/varieties that are hardy in this climate, zones 5 - 6, as possible. Careful examination of the labels provided with nursery stock is certainly advisable, and the labels should be saved for future reference. Using perforated baskets for potting up plants makes it easier to remove even fairly large plants from the pond when it is time to trim, divide, repot, or move them to different depths in the pond for winter protection.
Most of the commonly available free-floating plants such as water hyacinth and water lettuce are not hardy here. It is possible to keep them inside in a container of water in a sunny window or lighted aquarium, however their need for very bright light and warm water temperature makes it hardly worth the effort. It is more advisable to compost them in fall and purchase new ones next season. Duckweed is a hardy floater that will find its way into your pond in other plants you purchase.
Several plants with leaves that float on the surface are hardy and can safely remain in the pond. They may have better survival rates if their long tendrils are trimmed back to the pot and the pot is dropped a bit deeper in the water. Water clover, parrot’s feather, and water snowflake are examples of hardy plants in this category.
Marginal or bog plants offer a wide variety of hardy, vigorous choices that can be left in the pond to reemerge in the spring. Since they are confined to pots that prevent roots from reaching deeply into soil, many gardeners lower them a few inches below the level of ice formation. Some examples are: pickerel weed, marsh marigold, water iris (Iris psuedacorus), dwarf cattail, and arrowhead Other favorites such as Canna and Colocasia need to be removed from the pond to a place where the temperature remains near 50 degree. The tubers can be cleaned, dried, and stored in the basement. They also make attractive houseplants if they can be placed near a sunny window and kept moist. Another tender plant that is a favorite, the umbrella palm, can also serve as a houseplant; or clip off heads with a portion of stem, float them in water under bright light and they will quickly develop roots. Pot them and enjoy them inside until it is time to return them to the pond.
For many water gardeners whose ponds get sufficient sunlight, water lilies and lotuses are stellar performers. Their colors and fragrances can add another dimension of enjoyment to any size water feature. The foliage and spent flower heads of hardy varieties should be cut back and the containers dropped in the deepest part of the pond where the water will not freeze. Lotus need approximately the same treatment except that the foliage needs to be completely brown before it is trimmed. If, however, lotus must be trimmed while stems are still green, cut stems above the water level, or the plant will in effect drown. Water gets into the tuber through the hollow stems. If the pond is too shallow to prevent ice from forming all the way to the bottom, remove the plants, pots and all, to a place where they be kept cool, moist and dark. If they are allowed to dry out, they are finished.
Tropical lilies are difficult for water gardeners to resist because of their vibrant colors. There are some varieties that open during daylight hours while others open at night, and many are fragrant. Gardeners often treat them as annuals, but it is worth a try to over winter them. One of the following methods might work for you. (1) Store like cannas or dahlias, in damp sand at 60 degrees. (2) Clean and trim the tubers, then place them in airtight plastic bags of damp sand. Store the bags in the vegetable bin of your refrigerator. (3) Tropical lilies may also be stored intact in plastic bags in a dark place where they will not freeze. Check occasionally to monitor moisture. In late spring, repot them and return them to the pond.
There is no guarantee that any plant, water garden or terrestrial, will survive to grow another season, but it may be worth the investment you have in your plants to try. Some general practices will contribute to the health of the plants and fish in your pond. Prevent debris from building up on the bottom of the pond by covering it during the fall and keep decaying leaves and flowers trimmed from water plants. The decay process of a thick layer of leaf litter releases noxious gases and, if trapped in the water by a solid layer of ice, can be lethal to the fish and harmful to plants. Here again, as with any gardening endeavor, good sanitation practices pay dividends.