How to Decorate a Water Garden: A Complete Plant-by-Plant Guide
The best decorations for water gardens are achieved by combining floating‚ marginal‚ water lily and deep-water plants‚ rather than just dropping a water lily into a tub․ True depth comes from combining height‚ texture and flowering season for each type of plant‚ mimicking the natural characteristics of a pond or wetland edge․ Get that structure right‚ and everything else falls into place․
Tennessee gardeners have it made in this regard․ Much of the state is in USDA hardiness zones 6b to 7b‚ and many wetland and marginal plants make it through comfortably․ You're not fighting the climate‚ because the growing season is long enough for you to get plants established and filling out by their second summer․
Start With Structure: Marginal Plants at the Edge
Water depth for marginal plants is generally 1 to 6 inches (25 to 150 mm)․ They make up the backbone of a water garden and include cattails․ They can grow between 3 and 10 feet tall with flat blade-like leaves and distinctive brown flowering spikes․ Common cattail will grow in straight freshwater and narrow-leaved cattail will grow in slightly brackish conditions if your water source has any salt content․ Although the proper planting time is in spring after the last frost (immediately before or after mid-April in the Middle Tennessee area‚ couple weeks earlier in Shelby County in Memphis‚ couple weeks later up in the mountains)‚ a large thicket would be observable by the next spring․
One thing that people do not tell you about cattails is that they grow incredibly well via rhizomes․ If you have a small decorative pond‚ as opposed to a large water feature‚ plant these in a submerged container to prevent them taking over your pond within three seasons․
Ornamental grasses and sedges are well suited to this situation․ Sedges are especially forgiving‚ tolerating both wet and dry conditions‚ making them more adaptable to variable water levels caused by rain․ These plants may be stiff and upright or soft and arching so that two or three different sedges at the pond edge can suggest movement even when there are no flowers․
Native Wetland Plants Do Double Duty
This is where almost all the water garden books fail: it is the natives‚ not forgettable tacky exotics‚ that are the base․ Your native wetland plants in Tennessee are not only prettier and easier to grow‚ they are also adapted to our heavy clay soils‚ our summer heat and humidity‚ and you are not babying them through July․
Swamp milkweed is the superstar‚ a marginal plant that produces clusters of pink to mauve flowers throughout summer․ It is a host plant for monarch butterflies․ The marsh marigold is the harbinger of the season‚ flowering as early as March in the east‚ its shiny yellow petals opening before most of the pond has awakened․ Water willow and arrow arum provide a little variation in leaf shape‚ the wide arrowlike leaves contrasting with the stalks of the narrow-leaved grasses and sedges of the time․
New York aster deserves mention as most water garden lists don't have late season color‚ and this one carries the show from September into October and gives that pond or water feature a second wind․
Water Plantain for Structure and Wildlife Value
Water plantain is one of those inconspicuous looking plants that need to be looked at more closely to appreciate․ The plant is about 3 feet tall and has broad‚ pointed or rounded leaves․ The small pink or white flower clusters are held above the foliage on branching stems‚ like a baby's breath bouquet․ The ribbon-leaved plantain and the narrow-leaved plantain are both good fillers between your tall cattails and your groundcover‚ forming a mid-height layer in your planting․
Water plantain is not only an attractive plant‚ but a habitat․ The air cavities in the leaf provide a place for small fish to spawn and hide from predators․ With the large patches of it near the surface of the water‚ frogs and other creatures that inhabit the pond can easily find cover in it․ If you want a water garden that has a purpose as well as looks nice‚ this is definitely a plant to go for․
Duck Potato for a Bold‚ Reliable Bloom
Duck potato or common arrowhead is one of the easier marginal plants to cultivate․ It is a vigorous 2 to 4-foot (70 to 140 cm) plant with large arrowhead-shaped leaves․ It produces white‚ three petaled blooms on a tall stalk in late spring to early summer․ It will freely self-seed in full sun‚ constantly moist soil or shallow standing water․ This is a good or bad thing‚ depending on whether one wishes to cover a large area with it quickly or to keep it in a feature like that of cattails․
Layered Floating and Deep-Water Aquatic Plants
The categories above cover the shallows‚ but a truly well-decorated water garden still will have something going on in the 12-inch and deeper portions of the pond as well․ Deep-water emergents‚ such as water lilies‚ are plants that root in the soil and have leaves and flowers that float above the surface․ Floating plants‚ which are not rooted to the bottom‚ float on the surface of the water and lightly shade water; this considerably reduces algae growth during the humid Tennessee summers․
Submerged plants are always fully submerged․ Although more difficult to detect‚ they are very important to ponds․ Submerged plants provide oxygen and spawn sites for fish․ Ponds with only surface plants and no submerged plants will not be as clear‚ and are not supported well in temperatures higher than 85 °F (29 °C)․
Getting the timing and sourcing right
Most marginal and wetland plants prefer spring‚ as soil temperatures above 55°F (13°C) give the roots a full season to establish before winter returns․ Most hardier native plants will also survive a fall planting‚ but otherwise‚ you'll need to beat the first frost‚ which puts most plantings in the spring․
TN Nursery also carries many of these plants‚ including the cattails‚ sedges‚ and native perennials that thrive at the edges of ponds and streams‚ that are already acclimated to the Southeast‚ and save you some of the guesswork in finding suitable plants to survive a Tennessee winter․
A Final Note on Planning․
These plants not only make the feature look more natural‚ but they act as natural filters‚ oxygenate the water and provide protective habitat․ The result is a pond that does not become a green and algae-filled swamp by August․ One caveat to this is to check the eventual size and spread of the plants before buying‚ as some of those below (cattails‚ duck potato) will outgrow a small feature in two or three years․ A little research up front saves a lot of digging later․
