Outdoor artificial ponds are an excellent environment in which to keep aquatic turtles. Ponds have several advantages over aquaria including exposure of the turtles to beneficial natural sunlight, a reduced need for equipment (heaters, filters, heat lamps and broad-spectrum fluorescent lights) as well as water-conditioning chemicals, and the opportunity to introduce aquatic and marginal plants into the turtles' environment, creating a more naturalistic setting and providing natural, whole foods to supplement their diet.
There are basically two types of plants commonly used in and around ponds: aquatic and marginal plants. Aquatic plants are those which have leaves and roots but exist completely free-floating, either on the water surface (floating aquatics) or just below the water surface (submerged aquatics). Floating aquatics should never be placed in soil, but rather placed on the water surface and allowed to float freely. Submerged aquatics generally grow completely submerged (that is, under water). They are sometimes rooted in the pond bottom and sometimes float freely. Marginal plants are those plants which are rooted in soil but capable of growing with "wet feet", that is, at the margin of the pond or with their roots actually in the water. Some marginal plants are capable of adapting to conventional landscape situations, gardens with average irrigation; some require the bog-like conditions found in or near ponds and will not adapt.
As interest in water gardening has grown over the past several years, many unusual aquatic and marginal plants have become available through local retailers and mail order catalogues. In this article, the focus will be on less expensive, readily available plant materials. Because few people have a lake in which to keep their turtles, the plants discussed are all suitable for the small-scale pond. One bit of advice: many aquatic plants serve as food sources for aquatic animal life. Turtles can be voracious consumers of plants they relish. They are also very effective at flattening plants, breaking stems and generally rearranging their "furnishings". Before making a major investment in expensive plants intended for "permanent" pondscaping, it might be wise to introduce a single plant of the desired species into the turtle pond and see how long the plant lasts. For example, one-gallon named cultivars of water lilies run upwards of $30.00 each, making them rather pricey forage for hungry pond sliders.
Floating aquatic plants
Floating aquatic plants enhance the appearance of the pond. More importantly, they contribute to the health of the pond by cutting down on the amount of available light striking the water surface, thus checking the growth of algae. Coverage of approximately 60% to 70% of the water surface is generally recommended for algae control. Floating aquatics also act as "biological sinks", that is, they utilize mineral salts dissolved in the water, thus effectively competing with algae for available nutrients.
- Fairy Moss (Azolla caroliniana). A tiny floating fern, with fronds less than 1 inch (2.5 cm) long, it may spread to carpet the surface of the water. It reproduces freely and may multiply explosively and block out too much light. It may create a nuisance in a filtered pond by clogging the filtration system. It survives but is reduced by frost. Turtles keep this plant well under control as they enjoy eating it.
- Frog-bit (Hydrocharis morsus-ranae). Resembling a miniature water lily in appearance, its spongy, kidney-shaped leaves are about two inches across and it bears small, papery, white flowers in late summer. Plantlets borne on short runners enable it to form large groupings and to be easily propagated. It survives cold temperatures by dropping overwintering buds (called turions) to the pond bottom.
- Water Hyacinth (Eichhornia crassipes). The most common and widely available floating aquatic plant, water hyacinth is native to tropical America. Its smooth, circular leaves are attached to inflated stems which are honeycombed in the center, trapping air and providing buoyancy. Water hyacinth bears clusters of lilac flowers intermittently during warm weather. Feathery roots float below the water surface and new plantlets are produced on runners growing from the parent plant. Its form is more compact in full sun, more elongated in partial shade. Roots, stems and leaves of water hyacinth are eaten by many species of aquatic turtle. Possession is prohibited in Florida and Texas because it has created a nuisance by clogging open waterways, but being frost-sensitive it is less of a threat in other areas.
- Water Lettuce (Pistia stratiotes). With its vague resemblance to a loose-leaf lettuce, hence the common name, water lettuce forms rosettes of downy, pale-green, ruffled leaves; these leaves grow on swollen stems with a feathery root system under the water surface. Water lettuce grows best in partial sun. It is subject to occasional attacks by aphids and is sensitive to frost. Many turtles relish this plant. Possession of water lettuce is prohibited in Texas because it is a nuisance in open waterways.