Spring, summer, and fall maintenance is easy for water garden containers. Simply add water to keep it at the proper level and feed the plants and fish as necessary. Occasionally, the water may turn tea-colored though the decay of leaves or the pot may fill with unsightly debris. Empty the container, rinse it clean, and refill as quickly as possible to prevent the plants from drying out. Do not scrub the container clean as this will remove too many beneficial bacteria growing on the container's surfaces.
Winter maintenance depends on the type of plants, type of container, and the climate of the container's location.
There are three basic overwintering styles among water garden plants. First, there are aquatic plants that grow in cold northern climates and can easily handle being frozen solid. For example, think of cattails growing in a road side ditch in Minnesota. The second group is tropical aquatic plants that are never exposed to frost, and many won't even tolerate water temperatures dipping into the forties. These are plants like those that grow in the Everglades or the Amazon. In between these two extremes, the third group is aquatic plants that can tolerate cold water but not being frozen. Many of these plants have leaves and stems that die when the water gets cold, but the roots overwinter as long as they do not freeze. Hardy water lilies and lotus are good examples of this type of over wintering style.
If you live in a cold climate and have cold-tolerant plants, you can leave them outdoors as long as the container can tolerate being frozen. The tropical plants can be taken indoors and used as house-plants or they can be allowed to die with the cold weather. Some tropical plants require a lot of sun, so if there isn't enough sunlight coming in through the windows, they may not survive the winter anyway. Many of the third group of plants actually need a cold-induced dormancy period. If taken indoors to protect them from the frost, they will slowly die, and if left to freeze they will also die. If their pot can be placed at the bottom of a pond where they can have cold water without freezing they will survive the winter just fine.
If you live in a warm climate, you should stop fertilizing the plants for a few weeks in the fall to allow them to stop blooming as the day length decreases. When the plants begin to show active growth, they can be fertilized again.
If it is not possible to bring in the entire container of cold weather plants, it may be possible to just bring in the smaller nursery pots and place them in plastic bags or tubs with a small amount of water in a cool, dark basement until spring.
Another cold climate possibility is to use a bird bath or water garden pond de-icer to keep the container free of ice. If possible, move the container close to a building wall and wrap insulation around and over it. Deicers are not designed to keep the water warm - they just keep the water above freezing.
Tropical aquarium fish should be brought indoors long before the water gets cool. Goldfish can tolerate cold water, but they too should be brought indoors before the water temperature drops too much. If fish are placed in new aquariums, proper filtration will be required.