Water gardens are making a big splash

July 02, 2005|by JEFF RUGG /Copley News Service

Q: We started a water garden a couple of years ago. At first we had a hard time growing plants in the pond, but now they grow too fast and take over. I want to throw some of them in a nearby retention pond to make it look nice, but I am afraid the plants will take over that pond. I don't want to waste them. How should I get rid of them?

A: You definitely don't want to put them in the retention pond without permission. Some aquatic plants, just like many terrestrial of plants, are listed as noxious weeds and you could get into big trouble.

Most water garden plants are easy to grow. You can't overwater them and you generally have a hard time underwatering them. Many will grow with only a small amount of fertilizer left from the fish in the pond. Many have very pretty blooms and some shoreline plants will do well in rain gardens or in moist perennial garden beds. The ability to grow without much nutrition and in a variety of water levels from completely flooded to just moist soil might be good for the plant and good for the gardener, but it can also mean a plant that has the ability to be invasive into places that don't want it.


According to the National Gardening Association, in the past five or six years, the number of homes with some sort of garden feature that included water, quadrupled to about 16 million. At the same time, the number of invasive plants in new locations has also grown rapidly.

As you have found, many water gardens take a season or two to begin to mature and fill in. It is generally better for the whole ecosystem in a water garden to have some of the plants growing among the rocks and gravel, rather than in flowerpots. Many ponds have a shelf around the perimeter that can have a half campfire ring of rocks ranging from grapefruit to pumpkin size, depending on what can sit on the shelf. This ring of rocks is filled with gravel and then plants are placed in it. These plants take their nutrients out of the water. As the fish grow in size and number, the plants get more food and they grow faster.

Every pond is different, but some plants grow too fast to be taken out of the pot. It is easier to control their growth if they are left in the pot. As new roots or stems grow out of the pot, they can be cut off and thrown away.

Some aquatic plants don't grow in pots, they float on the water's surface. Water hyacinth (Eichhornia crassipes) and giant salvinia (Salvinia molesta) have roots that hang down in the water to take up nutrients, hide baby fish and to supply bigger fish with food. They both make excellent filter plants for backyard water gardens. They are both banned from sale in several southern states where they quickly fill irrigation and boating canals, streams and rivers. Many of these bodies of water have an abundance of nutrients. Consequently, the plants quickly cover the surface and block the flow of water and traffic and can block sunlight to native plants. Removal or control can be expensive. They both die with a frost, so for northern water gardens, they pose no threat and make great additions to backyard ponds as aesthetic elements and as filters. There is a possibility that in some middle latitude states, they could pose a threat in mild years and then die off in cold winters.

Since aquatic plants take up nutrients from pond water for their growth, they make good filters of the water. If you harvest some of these plants and use them in your compost pile or just toss them under your shrubs once in a while, you are harvesting excess nutrients from the pond and using them to feed your shrubs and perennials. This is a much better use of them than letting them go wild in nearby ponds or streams.

When building your pond, you should locate it so that if there is flooding, the plants and fish for that matter, won't wash downstream to other waterways.

Although many plants are not labeled or are mislabeled, try to figure out which plants are in your water garden and, when you buy new ones, try to get accurate information on what they are and if they are invasive. Just because a plant is listed as invasive for someplace doesn't mean it will be so for you.

I can't get flowering rush (butomus umbellatus) to grow in my pond and yet it is invasive for other people. The yellow flag iris (iris pseudacorus) in my pond has not grown out of a small area that it was planted in eight years ago, but it too is listed as an invasive. Unfortunately, because many plants have the ability to be ornamental in one location and a pest in another, they aren't all listed as invasive on any one list. Federal, state and local lists can easily have different plants listed as invasive for the area of jurisdiction covered. The list can be found at or

Probably the best rule of thumb is to never let any plant or animal go into the wild that wasn't already wild in that location. Any plant that grows too well for your pond, will probably do too well in the wild.

E-mail questions to Jeff Rugg at

Copley News Service

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