Get Your Feet Wet: Grow Wetland Herbs

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Dawn unfolds gracefully over Glimmer Pond.
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European brookline creeps over wet rocks.
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Butterfly weed
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Calla lilies
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Iris ensata ‘Geisha girl’

Although most of our classic herbs not only don’t like wet feet but require well-drained soils, many herbs thrive in wetlands. These valuable, aromatic, ornamental–but often overlooked–plants can provide a new gardening adventure for herb lovers who may be tired of the plain and mundane, have an “unusable” wet area in their yards, or plan to install one or more new water features. Wet, open places; seasonally wet meadows; swamps and acid bogs; pond, lake, and stream banks; and other waterside areas offer diverse habitats that can support a variety of unusual herbs. A virtually unlimited supply of water together with a rich supply of nutrients and full sun provide the ideal opportunity for these plants to thrive.

Herbs that thrive in saturated soils may be herbaceous annuals, biennials, or perennials, trees or shrubs, bulbs, or vines. They inhabit a number of different ecological niches. Some plants remain submerged beneath the water surface while others float on it with no attachment to the soil below. Still others are rooted in the mud, but their stems and petioles grow up to the water’s surface. Emergents or marginal plants grow in shallow water 1 to 6 inches deep, but most of their vegetative growth is above it. Bog plants grow in soggy, spongy, organic soils that never dry out. A final group of herbs, which includes many familiar garden inhabitants, thrives in ordinary moist soils.

Pond pros and cons

I have been gardening with wetland herbs for eight years, ever since I fell in love with Glimmer Pond, our half-acre earth-bottom pond containing an estimated 350,000 gallons of crystal clear water collected from underground springs, rainfall, and runoff. Although dreadfully overgrown when I first saw it, the pond proclaimed its health noisily through the voices of resident bullfrogs, green frogs, and spring peepers, and more quietly by the presence of mud turtles, mosquito fish, salamanders, and many kinds of dragonflies. I wanted to include useful herbs and showy ornamentals in this natural environment.

I soon discovered that precious little had been written about pond management for either wetland herbs or ornamentals. Although I found some historical information about medicinal herbs growing in wetlands, contemporary literature from the Cooperative Extension Service focused exclusively on techniques to increase fish harvests. These brochures recommended herbicides to kill marginal plants around the edges of a pond and fertilizers to increase the amount of single-celled algae (fish food), which would turn the water pea green. Quite the opposite of my objectives!

I eventually learned the basics of plant selection, planting, and maintenance at a daylong symposium on water gardening held at the Atlanta Botanical Garden. Ponds come in two basic types: earth-bottom ones such as Glimmer Pond and liner ponds. The latter type consists of a high-density prefabricated molded plastic form sunk into a hole of the same shape or a flexible sheet of butyl plastic 20 to 40 mils thick, draped in a hole of whatever shape you like. The plastic contains the water when a porous soil would cause it to drain away.

Planting an earth-bottom pond is a breeze. No soil preparation is required; either push plant roots down into the soft mud or smush them into a planting hole made with a trowel, then tap the surrounding mud back into place with your foot. Then stand back: growth is fast and exuberant.

If your pond has a liner, however, you’ll need to root your plants in containers filled with heavy, clay-based garden loam; the pots need not have drainage holes. Avoid using perlite, vermiculite, or peat, which float; avoid using manure as it encourages the growth of algae, which will cloud the water. The larger the container, the better your plants will grow, but the more muscle you’ll need to move it into the pond–a bushel-sized tub can weigh 100 pounds or more. Pond gardeners rely on fertilizer tabs or tree spikes to maintain good growth in heavy feeders, and they repot them with fresh soil at least every year–another awkward job. Wide, shallow containers are best; I like the kind with perforated sides to facilitate the exchange of dissolved gases between soil and water. A layer of gravel on top of the soil helps prevent the pond water from becoming murky and deters fish from rooting around plant roots.

Maintenance in an earth-bottom pond is a headache because the more aggressive rushes and reeds spread like wildfire, outcompeting choicer varieties. My least favorites are sawgrass, which cuts ungloved hands, and cattails, which are like the mythological Hydra with a dozen new heads springing up when one has been removed.

Wading into an earth-bottom pond is always an adventure: the mud has been known to swallow even a tightly tied tennis shoe. Liner ponds with no soil between containers limit the range of rampant spreaders and make wading easier and less likely to stir up mud.

Herbs for water

I have many favorite wetland herbs. Water mint (Mentha aquatica) grows in water up to 3 inches deep, and lilac flowers on stem tips are attractive to bees. The tastiest mint of all, pink- or white-flowered M. spicata ‘Kentucky Colonel’, grows in moist soil as does bee balm, whose leaves make a rather pungent tea. I particularly like the lavender blue Monarda ‘Blue Stocking’, rose-pink M.’Croftway Pink’, and brilliant M. ‘Cambridge Scarlet’. American mountain mint (Pycnanthemum flexuosum) spreads throughout my soggy hillside, with white bracts lasting for two months in the summer. (You can also use its leaves to make a tea.) Bog sage (Salvia uliginosa), with the softest baby blue flowers and a long season (April through October) of bloom, is another winner for moist soil that can also be used to make a digestive tea.

A plant of moist ground and streamsides, the stately 3-foot perennial cardinal flower (Lobelia cardinalis) has spikes of glowing scarlet flowers in late summer and a reputation as a vermifuge. A root tea of great blue lobelia (L. siphilitica), which blooms at the same time, was taken by Native Americans to treat syphilis. Both species do well for me, more than I can say for some of the ornamental hybrids.

The white flowered Eastern or lance-leaved water violet (Viola lanceolata) marches down to water’s edge. Like sweet violet (V. odorata), this species is used for perfume, cut flowers, and medicine. V. nephrophylla, V. obliqua, and V. palustris are other North American native violets of marshes and bogs. Many or most of the hundreds of species of Viola have edible flowers that are high in vitamin C.

Water forget-me-nots (Myosotis palustris) gently proliferate in moist soil and in water up to 6 inches deep. The tiny sky blue flowers with yellow eyes are enchanting both in the waterscape and for their “do not forget me” symbolism. ‘Mermaid’ is a more compact form with deep blue flowers.

The dusty pink flowers of swamp milkweed (Asclepias incarnata) attract butterflies in midsummer; Native Americans used a tea made from its roots as a purgative and emetic. In the wet herb garden, it combines beautifully with lavender pink Joe-Pye weed (Eupatorium purpureum), once used as a diuretic, and aromatic white boneset (E. perfoliatum), widely used as a flu remedy. Deep violet flowers of New York ironweed (Vernonia novaboracensis) tower overhead, and goldenrods (Solidago spp.) add brassy yellows to the late summer scene. Goldenrod flowers yield a yellow dye; its generic name comes from the Latin word solidus and refers to its traditional use “to make the spirit whole.” These native wildflowers brighten up the same wet hillside where mountain mint and turtlehead (Chelone glabra) bloom in early summer.

Double creeping buttercup (Ranunculus repens ‘Pleniflorus’) makes a dark green ground cover, rooting at each node, and bears shiny, patent-leather, double yellow flowers in spring. Its roots and leaves taste highly acrid and fiery, and have been used externally as a counterirritant in treating rheumatism and warts. The bright yellow blooms and shiny green heart-shaped leaves of another buttercup, marsh marigold (Caltha palustris), are spectacular at pond’s edge in early spring. It’s also been used as a folk remedy for warts. Because the weather is too warm for it in Atlanta, I substitute a European cousin, globe flower (Trollius ¥cultorum), which has larger, spherical flowers and grows in moist soil. The ground dried aromatic root of sweet flag (Acorus calamus) is added to potpourris to prolong the fragrance of other plant materials. The cultivar ‘Variegatus’, with 5-foot-long green-and-cream sword leaves, spreads easily in ankle-deep water. ­Although sweet flag was most commonly used to relieve digestive troubles, the Cree of Canada chewed the root as a strong stimulant and possible hallucinogen.

Arums bear tiny flowers on a curious fleshy spadix that is usually surrounded by a showy, sometimes colorful, leaflike spathe. Several native species grow in Glimmer Pond in water up to 6 inches deep. The wild calla or water arum (Calla palustris) and the white arrow arum (Peltandra sagittifolia) need no coddling. Their heavily veined arrow-shaped leaves are spiked with small white fist-shaped flowers. In January and February, glistening drops of water bead up on the bluish green ­velvety smooth leaves of golden club (Orontium aquaticum), and its pencillike, gold-tipped “clubs” (spadices) emerge above the water surface, adding interest to the winter waterscape.

Much showier but much more tender are the African calla lilies. In moist soil, the white spathe of Zantedeschia aethiopica unfurls to magnificent beauty around the yellow spadix, and I’m ­delighted to report that its rhizomes overwinter in Atlanta. In fact, neighbors have planted this species by their mailbox, in full sun and baking dry soil, and still it blooms reliably each spring. The golden yellow Z. elliottiana has large leaves densely spotted with white and also lives over winter. My favorite calla, Z. rehmannii, has an elegant waxy pink spathe that contrasts beautifully in ­texture with fluffy pink astilbes.

Several irises are indispensable to the herbal waterscape. The roots of blue flag (Iris versicolor) are strongly cathartic. ­Native Americans poulticed them on the skin to relieve pain and extracted a green dye from them. The vigorous ­yellow flag (Irispseudacorus) stands in a clump 5 feet tall by 5 feet wide in Glimmer Pond. In a.d. 764, Clovis, king of the Franks, determined that his army could safely cross a river via the shallows indicated by the yellow flags growing there, and attributed his resulting victory to the Christian God. As a consequence, the first of the French kings took the fleur-de-lis as his standard and Christianity as his religion. Double forms and a pale ecru variety are ­interesting variations of this spring bloomer. The Japanese iris (I. ensata) provides large, luscious blooms later in the season.

In summer, the clump-forming bulbous American swamp lily (Crinum americanum), a member of the amaryllis family, sends up scapes of several narrow-petaled white flowers like fireworks in the bog. The white spider lily (Hymenocallis caroliniana) blooms in spring in moist gardens in the Southeast. It is ­native from Indiana to Louisiana and Georgia.

Quamash (Camassia quamash), a member of the lily family from the ­Pacific Northwest, has an edible bulb and bears a 21/2-foot scape of pale to deep blue starry flowers in late spring. Its close relatives C. cusickii and C. ­leichtlinii add fine blue or cream flowers in March and April.

My white ginger lily or garland flower (Hedychium coronarium) spreads vigorously in the pond’s spillway; this native of India is hardy in Atlanta. The fragrant, edible flowers bloom in September and October.

Attractive quill-like foliage of Chinese water chestnuts (Eleocharis dulcis) thrive at a shady edge of Glimmer Pond, where it mimics the appearance of horsetail without its invasiveness (see below). The crisp, crunchy sweet flavor of the freshly peeled tubers is light years superior to the canned variety. I started my bed with a dozen firm tubers from a farmer’s market.

The weeds

The black-green jointed stems of horsetail (Equisetum hymenale) contain silica, making them effective pot scrubbers and earning them the name scouring rush. The stems are beautiful in flower arrangements, but a small clump can spread to a circle 30 feet in diameter in a year. Herbicides won’t kill it, and if you try to dig it out, the stalks break at every joint, and each piece roots. I wouldn’t dream of planting it in anything but a pot or tub.

Purple loosestrife (Lythrum salicaria) has 5-foot-tall spires of brilliant magenta pink that last for weeks throughout the summer. In fall, the leaves display orange and flame tints. Plant extracts kill bacteria and staunch bleeding. But this Old World species has no natural enemies in North America, and its aggressive colonization of wetlands crowds out native plant species and the animals that feed on them. Thirteen states have declared it a noxious weed and made it illegal to plant or sell it. Even the so-called sterile cultivars can be pollinated by L. salicaria and thus are not a safe alternative to planting the species, as was once believed. I planted three clumps of the cultivar ‘Happy’, but they declined and died in my warm climate; now only one clump remains to reflect its beautiful flowers in the water.

Herbal shrubs

I’ve added a number of herbal shrubs and trees to the moist areas of my property. Rosemary willow (Salix elaeagnos), a 6-foot shrub with narrow leaves that are a dark, glossy green above and felted white below, could easily be mistaken for a huge rosemary plant; its bark, like that of other willows, contains salicin, a chemical relative of aspirin with similar uses. Swamp rose (Rosapalustris), another 6-footer with purplish brown or reddish spiny stems, has terminal clusters of 2-inch pink flowers in summer that I use to make rose-petal jam. Swamp bay (Magnolia virginiana) is a narrow, open, evergreen tree with narrow yellow-green leaves. I love the lemon fragrance of its creamy flowers that open in May. The deciduous swamp azalea (Rhododendron viscosum) bears clusters of white to pinkish-tinged long, slender, funnellike flowers with a spicy fragrance in early spring. It prefers low, marshy areas and stream banks. Hybrids between this and other native azalea species also do well here. I pinch the stem tips of the young plants to encourage bushiness.

The king and queen of aquatic herbs

The sight of water lily pads on the surface of still water is magical and brings to mind Monet’s paintings. Water lilies (Nymphaea spp.) are antiseptic and astringent; mucilage in their stems has been used as a soap substitute. The rhizome and seeds of several species are edible. The rhizomes grow submerged in the mud, sending up petioles as long as need be to get the leaf pads to the surface. Hardy lilies typically float their flowers on the surface and give the gardener little trouble because they winter in place. But if you’re after blue flowers, or a flower that opens during the cocktail hour, you must choose a tropical water lily, grow it in a large container, and drag it inside under cover before hard frost. The ancient lotus (Nelumbo spp.), waving huge shield-shaped leaves up to 6 feet above the water surface, is a striking sight.

Its beautiful flower or seedpod is the symbol of several ancient religions (Egyptian and Persian); its rhizomes are sliced and used cooked or raw in salads.

Whether large or small, simple or elaborate, sunny or shady, permanent or seasonal, open water or marsh, still or moving, water is indispensable in the landscape. Light reflects off its surface, and the effect of flower and leaf colors is doubled by their reflections in it. I invite you to add water to your own herb garden.

Horticulturist Geraldine Laufer lives and gardens outside Atlanta, Georgia, and was awarded “best garden in Georgia, large garden category” for her work on Frog Holler by the Garden Club of Georgia.

Further reading

Erichsen-Brown, Charlotte. Medicinal and Other Uses of North American Plants: A Historical Survey with Special Reference to the Eastern Indian Tribes. 1979. Reprint, New York: Dover, 1989.

Heritage, Bill. Ponds and Water Gardens. 2nd ed. London: Blandford Press, 1986.

Matson, Tim. Earth Ponds. Revised 2nd ed. Woodstock, Vermont: Countryman Press, 1991.Nash, Helen. The Complete Pond Builder. New York: Sterling, 1996.Slocum, Perry D., and Peter Robinson with Frances Perry. Water Gardening: Water Lilies and Lotuses. Portland, Oregon: Timber Press, 1996.Tomocik, Joseph. Water Gardening. New York: Pantheon Books, 1996.

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