Because planting a floating plant involves nothing more than placing it in the water, the main concern is keeping their reproduction under control. Too many floating plants can lead to depletion of oxygen levels in no time. In shallow ponds, especially during summer, the plants can actually trap heat within the pond which will lead to the water temperature rising to dangerous levels. On the other hand, too much coverage during a rainy day or abrupt change in temperature can result in the upper layer of water which is also warmer and more oxygenated to mix with the lower layer of cooler and less oxygenated water. This is called turning and will prevent sufficient oxygen exchange and will stress out any fish that are present.
To avoid this, excess plants should be removed. Duckweed multiplies at an incredibly fast rate in early spring. Even though the surface coverage will discourage the growth of algae, it can easily overrun your pond. The common type of Duckweed, Lemna minor, is usually kept under control by the stomachs of your fish. However, larger Duckweed doesn’t seem to interest fish and should be kept or pulled out of the pond. You will notice less of this plant in the hot summer months but if it is still a nuisance to you, removing excess or all of this plant in the spring and fall will be in your best interest.
Another floating plant, Water Meal, is a tiny plant that looks like fine grit that hangs out in clumps along the pond’s surface. Like Duckweed, Water Meal can overtake your pond in the blink of an eye. If your fish are not up to the challenge of eating the Meal to keep it under control, a copper or simazine treatment may be necessary to get rid of the problem.
Frogbit reproduces by growing side-plantlets that break off to multiply on their own. Frogbit roots in shallow pots of marginal plants and will create matting around the pot. Luckily, excess plants can easily be pulled out by hand. Frogbit doesn’t generally make it through winter. You can attempt to bring in some Frogbit before the first frost and keep it alive indoors, but people who have done this have found that they don’t grow back as nice in the spring.
Water Lettuce and Water Hyacinth are both tropical floating plants. They multiply through plantlets that are sent out off of the sides. Hyacinths bloom a pretty purple flower that lasts only a day. Water Lettuce is a favorite among fish for a snack. These plants make great additions to the compost pile because they absorb minerals from the water. Any excess plants are easily removed by hands and can be grown indoors during the winter but success at this is dependant on how well they’re kept and can be expensive. Tossing them out at the first frost and purchasing new ones the following year may be your best bet.