While everything else was wilting in the latest heat wave (people and plants alike), there was one group of plants that keep their cool. With at least their feet in the water, all the many interesting flora that grow in and around ponds, lakes, and streams took the high temperatures in stride. Water gardens of all sizes-from glazed ceramic pots and half wine barrels to stone basins and deep koi ponds-are greatly enhanced by a selection of these water-loving plants, and they are a part of the natural aquatic ecosystems that we try to mimic in our water gardens.
The most well-known and beloved aquatic plant is probably the water lily. Most ornamental water lilies are in the genus Nymphaea. They can be subdivided into the hardy and tropical types. Hardy water lilies begin their spring growth in February, and the first blossoms appear in early March continuing into October. When the nights begin to cool, hardy water lilies will stop blooming and put out smaller leaves, usually retreating to a rosette of inch-sized leaves just above the water lily crown. The dormant plants are left in place in the ponds through the winter months. Hardy water lily species and hybrids come in most of the colors of the rainbow, although they tend toward the pastel instead of vibrant. White, yellow, pink, and red flowers can be found in sizes and shapes from the tiny and starry to the robust and double-flowered. Both flowers and leaves float right on the surface of the water.
Tropical water lilies will not begin to grow until late May or early June, when the night water temperature nears 70 degrees. They grow very rapidly, blooming in the first month, increasing in size and number of blooms until October or, given a mild autumn, Christmas. Then they usually become dormant and no leaves are seen until the following spring. Many varieties of tropicals will not survive even our mild winters. They can be held in heated tanks through the winter or treated as annuals. While hardy water lilies offer subtle color shades, tropicals are truly electric. In addition to the yellows, pinks, and reds, there are species with blue flowers. Many hybrids have been developed to show off these spectacular colors. Most tropicals have a regular daytime bloom period just as the hardies do, but there is another group whose blooms open only as the sun is setting and remain open all night, closing about mid-morning. Tropical water lily flowers are held on tall stalks above the surface of the water and are very fragrant.
A few local nurseries sell a limited number of water lilies, both tropical and hardy. Many more cultivars are available through mail and on-line catalogs. If you purchase your water lily already potted up, it will have a suitable growing medium. If you obtain your plant as a bare root tuber, plant it in regular garden soil, not a commercial mix containing organic components. During the growing season, fertilizer tabs or stakes can be easily inserted into the pot to keep plants vigorous. Most water lilies appreciate a steady supply of a balanced fertilizer. When planting, mix a handful in with the soil in the bottom half of the container (this will reduce the amount that leaches out into the pond to feed unsightly algae).
There are lots of other aquatic plant choices. In pots at the edge of the pond, you can plant iris (Iris pseudacorus, I. kaempferi, and a group of hybrids known as Louisiana iris), pickerel weed (Pontaderia cordata), cattails (Typha species), water canna (not a canna, but Thalia dealbata), water chestnut (Eleocharis dulcis), papyrus and its diminutive relatives (Cyperus species), and arrowhead (Sagittaria species). Plant them in the same manner as water lilies, but submerge their pots just a couple of inches under water. Another group of plants float on the surface with their roots dangling down to take nutrients directly from the water. These include water hyacinth (Eichornia crassipes), water lettuce (Pistia stratiotes), water fern (Salvinia species), and duckweed or frog bit (Lemna species).
If you don’t have a water garden of your own, make a visit to Alice Keck Park Memorial Garden and stroll along the stream or picnic on the edge of the large water lily pond. Lotusland also has displays of hardy and tropical water lilies and bog gardens full of arrowhead, papyrus, and taro as well as their namesake, the lotus (Nelumbo species and cultivars). Their annual celebration, Lotusfest, is on Saturday, July 19. Check out details at lotusland.org