WATER GARDEN TIPS FOR FALL

The days are shorter, the weather is cooler, and most water gardeners cannot believe that pond season is slowly coming to an end. To those who garden with tropical plants in containers or very shallow ponds, fall signals the time to move water gardening inside, either to tub gardens or aquariums. To others, it means closing down the pond until next season – and overwintering hardy plants and fish outside - in ponds at 30 inches deep or more. In either case, properly preparing plants and fish for the coming winter months will help eliminate many problems that pond owners encounter at pond opening in the spring.

Cleanliness and Pond Water Quality

Colorful autumn leaves are beautiful to look at in the landscape, but detrimental to pond water quality if left in the water to decompose . Ideally, the garden pond is not located under a tree – however, many of us have ponds near, or even partially under, a tree canopy. Even ponds sited well away from trees can collect blowing leaf litter in the fall. If left to decay in the pond, leaves provide nutrients for algae. The result is a fall algae bloom;, and there are fewer plants to compete with algae for nutrients and light. Also, many leaves contain tannic acid, which give the water a brown cast - and at certain levels, tannic acid can be toxic to fish.  Ponds skimmers help keep leaf contamination to a minimum. Checking and emptying the skimmer bags may need to be done daily during heavy leaf fall, to prevent recycling water through a "compost tea-bag."

Leaf netting also helps prevent leaves from entering the pond – the finer the net texture, the more types of leaves (i.e. pine needles) it keeps out. Black pond leaf nets are barely visible, and blend into the garden. Dark colored fiberglass screening, loosely woven shade cloth, and even tulle netting available at fabric stores can be used as leaf netting. It is best to make sure the net stays above the water surface, to keep nutrients in the leaves from leaching into the water. Netting can be stretched tightly across the coping stones at the pond border and anchored with additional bricks or stones. Large row-cover hoops (available at garden supply sources) or simple sawhorse-type frames can also be constructed to support netting. Periodically, the netting should be removed and shaken out, so that fall winds don’t shatter the leaves and blow the smaller particles through the net. If horizontally blowing leaves are the problem, netting can be stretched, fence-style, around the pond, at the height of a few feet.

Spent leaves and flowers of water plants also should also be removed immediately, for the same reasons stated above. This should be done throughout the pond season, and is imperative at this time of year. Tropical free-floating plants, such as Fairy Moss, Water Lettuce and Water Hyacinth, should be netted out as they die. They make great additions to the compost pile, having spent the warm months filtering nutrients out of the pond water.

Water Plant Care

Hardy aquatic plants need to prepare for winter dormancy, so encouraging lush growth by fertilizing in late summer and fall is not recommended. Dis-continue fertilizing until growth resumes in spring, even if overwintering tropical plants inside. Although tropical plants generally don’t become dormant, they do "rest" - producing fewer leaves and perhaps ceasing flower production until the days lengthen as warm weather approaches.

Hardy water lilies will slow down flower production in the fall, and production of new lilypads will eventually stop. A small, flat, indicator leaf will emerge on a short stem near the crown of the plant – this leaf "reads" the amount of light available, and will bring the plant out of dormancy as days lengthen in the spring. Remove all leaves but the indicator leaf, and sink the entire pot to the ice-free zone at the bottom of the pond – usually a water depth of 30 inches or more. If this is not possible, try trimming back as described, then wrap the potted lily in wet burlap or newspaper and place inside a styrofoam cooler or plastic bag. Place where temperatures stay below 55 degrees, but above freezing. Since the plant is dormant, light is not necessary at this point. Check the pot periodically, to be sure that the soil stays evenly moist. When there is no chance of the shallow pond freezing to the bottom (in late winter/early spring,) refill the pond, divide and repot the lily if needed, and return outside. The indicator leaf will cue the water lily to resume growth.

Tropical lilies are often treated as annuals in our area; however, there are many Midwest water gardeners who have successfully carried tropical lilies through the winter. One method that works for smaller varieties is to place them, pot and all, in a large tub or aquarium. Keep the water temperature near 75 degrees, and provide bright light - either in a sunroom or greenhouse, or by using supplemental lights. Many won’t flower, but most will keep their leaves. In spring, when outside water temperatures stabilize above 70 degrees, the tropical lily can be placed back in the pond.

Another method of overwintering tropical lilies is to allow them to stay in the pond until the second frost, to "harden off" the tuber. Remove the tuber from the pot, hose off the soil, and cut off the remaining leaves and roots. Seperate the smaller tubers from the mother tuber. Treat with a fungicide, and store in moist sand or in a jar of distilled water at a temperature of 50-55 degrees F. Do not allow the lily tubers to dry out if you store them in sand – check the moisture level periodically. If storing in water, make sure the water doesn’t have a foul odor or discoloration - this indicates rotting, and the tuber should be discarded. Changing the distilled water in the jars will sometimes help the viability of the tubers. About four weeks before the pond water will remain above 70 degrees F, repot the tubers in small pots. Submerge them in water and place in a warm, sunny window, heated aquarium, or greenhouse.

Most hardy marginal plants are cut back and lowered to the ice-free zone in the pond – Pickerel Plant is a good example - but many will do well if they are removed from the water and spend the winter in empty spaces in the perennial garden. Remove the pot from the water, and sink to the rim in the garden – or "plant" the pot. Mulch well after the ground freezes solid. Japanese Iris, Louisiana Iris, Marsh Marigold, most reeds and rushes, and cattails respond well to this treatment. Reeds, rushes and cattails can also spend the winter on the marginal shelves of deeper ponds that don’t freeze solid. Remember to cut back the stems above the water line - if the hollow stems are below the water, they act like straws, drawing water into the crown of the plant, causing decay. As long as they don’t fall into the water, the upright stems can remain to provide winter interest in the water garden.

Tropical marginals are easily raised as houseplants during the winter. Use a non-porous outer pot, drop the potted marginal plant into it, fill it partially with water, and place in a sunny window. Dwarf Papyrus, Copperleaf, Dwarf Sweet Flag, and Water Poppies are good candidates for this treatment. Water Cannas are an exception – after frost blackens the leaves, remove the pot from the pond and cut off the leaves. Take the rhizome out of the pot and rinse off the dirt , then air-dry for a few days in a temperate place. From there, store in paper bags, as you would garden cannas, at a temperature between 50 and 60 degrees.

Hardy submerged oxygenating plants will overwinter in the ice-free zone of the pond. Take six inch tip cuttings, band them together, and sink them to the bottom using a small rock or lead weight. Discard the soft, brown, older parts of the plants. Some oxygenators, such as Hornwort, produce thick, darkened clusters of leaves at the stem tips. These winter buds drop to the bottom of the pond, where they sprout the following spring. Most oxygenators can pull double-duty in fish tanks over winter – many are the same varieties that are found in pet stores.

Fish Care Outdoors

Hardy cold water fish, such as goldfish and koi, easily spend the winter at the bottom of the pond, as long a few conditions are met. The water quality must be very good before turning off the filter and pump for the winter. Poor water quality stresses the fish, so they enter the winter in less than peak condition. This invites disease and parasite infestations at a time when fish immune systems cannot function. If the water quality is good when the filtration is shut off, problems are minimized. When fish don’t eat, (during the winter) they don’t produce waste products, so there is no imperative need for filtration.

The water temperature must remain fairly constant during hibernation – even with an ice cover, at a three-foot depth, the water stays between 50 to 55 degrees F. Try not to disturb the fish or the temperature stratification of the pond water during the winter rest period.

A hole in the surface ice for gas exchange is must be maintained throughout the winter, so that toxic gases from any leftover decaying materials don’t poison the fish. The opening can be as small as six inches in diameter, and is easily maintained by raising the water pump to within 8 inches of the pond water surface, so that the water remains agitated. (Moving water seldom freezes.) Some water gardeners use larger versions of aquarium air pumps and airstones, which cause turbulence at the water surface. If choosing this method, be sure to use a pump designated for outdoor use. Plastic airline tubing becomes brittle and may crack when frozen, so use silicone, not plastic tubing.

Fish must have sufficient fat reserves built up prior to winter, if they are to survive winter outdoors. Ideally, the fish should look very fat – even males should look pregnant – before entering their winter rest. Feeding the right food, in the right amount, is very important. While the water is still above 60-65 degrees F, feed them as much as they will eat in five minutes, several times each day. Make sure to remove any leftovers to avoid polluting the water. As the water cools to between 55-60 degrees, fish metabolism slows down, and they will show less interest in feeding. Switch to a wheat germ based food, which is easier to digest - feeding the fish as much as they consume in five minutes, once per day. Once water temperatures drop between 50 to 55 degrees, feed only two to three times per week. Fish cannot digest when water temperatures remain below 50 degrees, so at this point, stop feeding altogether. Even if there is a warm winter day, the water temperatures will drop again at night, leaving undigested food in the fish’s digestive tract - and it is possible for illness or death to result. While hibernating, fish will hover, nearly motionless, in the warmer water at the bottom of the pond. Once spring arrives, activity will slowly resume – at this point, follow the fall feeding schedule, but in reverse order.

Putting the pond to bed correctly in the fall will make pond opening in the spring a much easier and more enjoyable task. Plan on spending next spring enjoying clean, clear water, healthy fish, and vigorous plants!

Date: September 2000
Author: Lisa Calvo Goering