Saturday, August 02, 2003

By Amy Nelson, Phipps Conservatory , and Botanical Gardens

Beneath the water lilies, lotus, boggy bog and marginal plants lies the world of oxygenating plants. These plants are very important in establishing a healthy and balanced pond.

	The key to healthy water plants like waterlilies are their decidedly less glamorous cousins such as Anacharis and sagittaria. These low-growing oxygenating plants help maintain a balanced growing environment. (Bob Donaldson, Post-Gazette) Related information Free day at Phipps Conservatory

They are completely submerged, either planted directly into the soil at the bottom of the pond or in a pot and placed in the bottom. Oxygenating plants absorb impurities in the water and help prevent algae growth. They also help cool the water much the same way a shade tree does.

If you have fish in your pond, oxygenating plants absorb the carbon dioxide fish give off and release oxygen for them to live. The plants also provide a food source, either the plant itself or by being a home for other organisms. Oxygenating plants also provide shelter and a place for fish to spawn and lay eggs.

These plants help control algae since they both compete for the same food source. Oxygenating plants absorb nutrients directly through their stems and foliage, helping to keep pond water clear and clean.

Planting oxygenators is similar to planting water lilies, except that the container does not need to be as deep and the soil needs to be heavier, with a high percentage of gravel and sand or gravel alone. If you use soil, top off with pea gravel to keep the soil from floating out of the container.

Usually sold in bunches of five, these plants can be difficult to establish. Plant a variety of types, one bunch for every 2-3 square feet of pond. There is no need to fertilize oxygenators at planting or any other time.

Koi and goldfish love to nibble on the foliage of these plants. If you have fish that are over 6 inches long, allow newly planted oxygenators to become established before placing them in the pool. Until they are established, you may wish to grow some other plants in a separate container to help replenish what is eaten. Or you can protect the plant from hungry fish using a plastic mesh. The mesh, available at an aquatic plant supply store, creates a dome over the container.

Plants to try

Here are a few hardy oxygenating plants to try in your pond:

Anacharis (Elodea canadensis) is one of the best oxygenators for all ponds. It has slim, fernlike fronds covered with dark green leaves. Anacharis grows right up to the water surface and produces tiny floating white flowers on trailing threadlike stems in summer.

Dwarf sagittaria (Sagittaria subulata) has dark green, grassy foliage and produces small white flowers in summer. It spreads by producing runners and is a strong-growing plant.

Jungle vallisneria (Vallisneria americana) has light green translucent ribbons of foliage. It is a strong grower and can reach 6 feet, producing tiny, non-showy flowers in early summer.

These oxygenating plants are hardy in our zone and can be wintered over if left where they are until spring. On sunny days in the winter, the fish will swim around, nibbling. The plants may look ragged by time spring arrives and will benefit from some trimming. You also can treat these plants as annuals and start with all new ones the next season.

When you come to Phipps Conservatory this summer, be sure to visit the lily ponds. To purchase oxygenating plants, check local nurseries.

For answers to all your gardening questions, including those on oxygenating plants, call Dr. Phipps' GreenLine at 412-665-2364. A master gardener will return your call with the answer to your question. Visit the horticulture library at Phipps Garden Center to find information on all aspects of gardening.

This is one of a series of periodic columns by staffers of Phipps Conservatory and Botanical Gardens. Amy Nelson is a grower at Phipps.

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