Aquatic Plant Care in the Fall – Fall Finale

Published on August 13, 2009


Shorter days, cooler nights and a decrease in hardy waterlily blooms are sure signs that another water gardening season is almost at an end. With the change of seasons comes the time to winterize.

Until that first freeze arrives, there are many maintenance items that need to be performed. Yellowed lily pads and spent blossoms should be removed at the crown. All dead or dying plant material in the pond should be removed. As leaves begin their annual descent, remove all which blow into the pond. If deciduous trees are in close proximity to a pond, bird netting can be stretched taut over the pond surface to keep leaves from polluting the pond. This will decrease spring pond start-up efforts. Ponds with a skimmer should be monitored so leaves do not obstruct water flow, causing the pump well to dry up and burn up the motor. Water flow can slow or stop when warmer water temperatures and a decrease in surface coverage by plants, combined with cooler ambient air increasing evaporation, drops the water level below the skimmer intake.


If fish are being overwintered, their health is dependent on maintaining a balanced environment. A cleaner pond going into the dormant season decreases stress that may increase susceptibility to life-threatening disease organisms and parasites resulting from poor water quality. Partial water changes will decrease concentrations of nitrates left behind after natural bacteria break down excess food and decomposing organic matter in an ecologically-balanced pond. Keep mechanical and biological filters clean until they are shut down for the season. Biological filtration decreases in efficiency when temperatures fall below 68° F. and cease functioning at 42° F. When water temperatures drop to 50-55° F, it is best to discontinue feeding fish their normal diet. If fish are showing an interest in eating, a spring and fall food that is easily digested can be offered until water temperatures drop to 40° F.

If waterfalls are shut down for the winter; pumps and filters being removed from service should be cleaned and stored in an area where they will not freeze. Waterfall boxes with filters should be cleaned, removing silt and detritus. Pumps left in the pond should be cleaned and returned to the pond. An open area needs to be maintained for fish when the surface freezes. This will allow life-threatening toxic gases to escape. A small pump in the pond with the outlet one to two inches below the surface will keep an area open in mild freezing conditions, as will an aerator. De-icers are more effective for extended sub-freezing conditions. Also, waterfalls and streams provide moving water that is less likely to freeze.


Plants need special care for successful overwintering. Many water plants are perennial plants, meaning they will endure for a number of years, going dormant during the fall and winter seasons and returning the following spring season in colder climates. Plants usually have identification tags with temperature ranges for growing. USDA hardiness zones provide guidelines for determining which plants can remain in the pond. After the first significant frost, remove all dying and dead plant material in the pond. Excess “oxygenators” should be removed, as well.

Hardy Plants

Hardy waterlilies, lotus and hardy emergent plants should be placed at a sufficient depth to avoid freezing of plant crowns. Cutting away the dead stems from emergent plants can be left until spring, adding winter interest to the pondscape. Division of waterlilies and emergent plants should be done in the early spring as new growth appears.


If the pond is too shallow to over-winter plants, they can be moved to a basement or garage where they will not freeze. Leave plants in their pots, wrap them with damp newspaper and place them in a plastic bag. Make sure to keep newspaper and soil damp, but not wet enough to cause rotting.

Tropical Plants

There are a number of perennial water plants that are not winter hardy in many regions due to temperature extremes. These plants are often referred to as “tropicals.” These plants can be overwintered or treated as an annual plant to be disposed of at the end of the growing season. If overwintering, they should be brought inside before temperatures drop to 60° F. If plants are left out too long, they begin to start to move toward dormancy, thus making the adjustment to the indoor environment more stressful. Before you bring plants into the house, sunroom, or greenhouse, inspect them for insects.

Most insects can be dislodged with a hard spray of water from the hose.

Many plants do very well when cared for as houseplants. They do not need to be submerged in water, but should only sit in a water tray to maintain wet soil. Plants should be placed in a brightly-lit area to avoid stress that encourages insect infestation.

It is a good idea to hang a few sticky fly strips near plants to catch annoying gnats and other flying insects looking for a place to live. It is important to watch for any insect increase that may arise and treat promptly, before they get out of control. If any bugs are visible, crush them with your fingers or, if you are squeamish, use a q-tip. White flies, spider mites, aphids, and mealy bugs are among the hardest to control if you let populations get out of hand. A hard spray of water from the shower should be tried first. A soapacide can be used as an alternate method. Some plants may be sensitive; treat one leaf to see if damage results. As plants will return to the pond, insecticides should be avoided. Systemic insecticides should never be used.

Plants should not be fertilized again until the following spring, just prior to being returned to the pond. At that time they can be pruned and/or re-potted.



Another method of keeping plants for the following season is through cuttings. Water Forget-Me-Not (Nasturtium aquaticum), Blue Bell (Ruellia brittoniana), and Wedelia (Wedelia trilobata) are some of the most-easily-propagated. Cuttings can be placed in water, in bright light. Add water as needed and change the water if it develops an odor. When a good root system emerges at the “jointed” points on the stem of the plants, they can then be potted and maintained by placing in shallow water as discussed above.

Tropical lilies can be over-wintered by one of two methods. As the water temperatures cool, tropical waterliles will develop tubers that will make new plants in the spring. They will be found during a search through the soil. Tubers can be stored in jars or zip-lock bags of moist sand in cool, but not cold, conditions. The other process is to maintain optimum growing conditions with heated water and artificial light throughout the winter. Fertilize monthly to encourage continuing growth.



Debris – dead and dying material in the pond needs to be removed. The process of decomposition removes available oxygen and releases carbon dioxide, affecting (even killing) fish and other living organisms.

A clean pond at the close of the growing season improves water quality, decreasing algae in the spring.


Algae is feed by sun, excess nutrients and low levels of oxygen. In spring it is not unusual to have some algae until plants begin to grow. Waterlily pads shade the water and growing emergent plants take up excess nutrients. Many algae control methods kill algae, but it falls to the bottom of the pond, creating nutrients to feed new algae.

Japanese Koi Kodama

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