Marginal, or shallow-water, plants are those that live with their roots under the water but the rest of the plant above the surface, they also occur naturally along the edges of ponds and streams and usually like water over their roots at least part of the growing season. These are usually placed so that the top of the pot is at or barely below the water level.
These are the ones to plant just inside the margin of your water garden. If your pond doesn’t have built-in planters or plant shelves, you’ll need to raise the plants containers on blocks to the depth where they grow best. Generally 2-gallon containers will do for all but the largest and smallest plants. Except for the rampant spreaders, marginal make excellent plants for tub gardens. Some species also thrive in garden beds if the soil is well amended with organic matter and kept moist.
These should be put in heavy soil, covered wtih cinders of lava stone, and place them at the depth recommmeded by your supplier.
Maintaining Marginal Plants
Marginal plants should be regarded rather like those in the herbaceous border and lifted as necessary. There are great differences between the rates of growth of, say, a rampant reedmace and the more measured development of a skunk cabbage. Once a plant is identified as being overcrowded, remove it from the pond and divide it, ideally during the spring. This gives it the opportunity to develop into a reasonably mature and attractive plant during the first growing season. Dividing up a plant once growth is under way not only results in a less attractive specimen, but often impairs flowering as well. Irises are the only plants to benefit from dividing during the summer. If they are disturbed during the spring, then summer flowering will be greatly affected. Lifting and dividing irises immediately after they have flowered, gives them an opportunity to become well established for the following season and then make a fine display. Do not be nervous about cutting the foliage back hard and separating the clumps into individual fans of leaves. Be sure to trim the roots back sharply before replanting.
For the majority of aquatic plants, division is simply the process by which a crown is separated into sustainable portions that are potted or planted out individually. In the case of plants such as reedmaces and rushes, which have creeping root systems, this often involves removing lengths of rootstock, each with a terminal bud, trimming these up and potting them individually. Effectively, each division is a large bud or shoot with a small cluster of roots.
Recommended Marginal Plants
Acorus calamus Sweet Flag
Description: The strap shaped foliage of this perennial looks for all the world like that of an iris, or “flag,” but its midsummer flowers are underwhelming 2 inch horns. The leaves smell like cinnamon if you crush them, and can be 4 feet tall. The cultivar “Variegatus” is striped from top to bottom with white or cream.
Grow sweet flag in water up to 9 inches deep or a well-watered flower bed. Zones 4-11
Alisma plantago-aquatica Water Plantain, Mad-Dog Weed
Description: It has lance shaped gray-green leaves about 1 foot long from spiky rosettes, which are topped with frothy sprays of tiny pink or white flowers reaching up to 30 inches.
The baby’s breath of marginal, water plantain will self-seed and is too vigorous for small ponds. Plants do best in water 6 inches deep.
Butomus umbellatus Flowering Rush
Description: Native to North America, Europe, and western Asia, this 3- to 5- footer has twisted, strongly vertical leaves ½ inch wide, which are bronzy purple when they’re new. Fragrant, cup-shaped, rose-pink flowers appear in 4-inch-wide clusters in late summer.
It can grow in water up to 5 inches deep. Divide it frequently if you’re growing it in a container. Zones 5-11
Calla palustris Bog Arum, Wild Calla
Description: Bog arum, in the same family as jack-in-the-pulpit, has a flower similar to that of the South African calla lilly. A nearly round spathe cups the green-and-yellow club of the spadix; after a long season of bloom, flowers are followed by red-orange berries. Its 6- 20- inch rhizome creeps along the soil surface with shiny, leathery, heart-shaped leaves, spreading to about 2 feet.
Give it full sun and water to a couple of inches deep, or plant it in wet pond side soil heavily amended with peat moss to increase its acidity. Zones 3-8
Caltha palustris Marsh Marigold
Description: The bright yellow flowers of this spreading native look more like buttercups than what we usually call marigolds. Growing from rhizomes to about a foot tall, it has toothed kidney-shaped leaves. The cultivar “Flore Plena” (also sold as Multiplex) has double flowers. Marsh marigold likes water only a few inches deep.
Flowering period is from March to July. Propagation can be done by divided seeds in late summer. Zones 3-7
Colocasia esculenta Green Taro
Description: Every water garden deserves at least one elephant-leaved perennial, even though most can be challenging. Cultivated as a root vegetable in Southeast Asia, taro has 2-foot arrow-shaped leaves on 3-foot stalks. Look for the cultivar ‘Fontanesii’, which has violet stalks and leaves that glow with dark red veins and margins. 'Hilo Beauty’ has white mottling: ‘Illustris’ has dark purple mottling and stalks.
All like high humidity and filtered sun. It can be planted 12 inches under the water. In Zone 8 and north, store the tubers (dry) over winter in a place where they won't freeze.
Zantedeschia aethiopica Calla Lilly
Beloved by florists this 2 to 3 foot tall bulbous plant from Africa can be grown as a marginal aquatic in warm climates, although it is almost too beautiful to look at home in an informal pond.
Its shiny leaves are arrow shaped. The cup-shaped fragrant white flower (spathe) surrounds a club, or spadix.
Grow calla lilies in a container of heavy soil under a foot of water. They can also be grown in garden beds; they tolerate a wide range of soils provided the soil is moist or they get regular watering.
Eleocharis montevidensis Spike Rush
Description: Spike Rush (Eleocharis montevidenis, also sold as E. palustris) this plant also goes by the name of fiber-optic plant (as do a couple of completely different plants with a similar shape). Spike rush occurs naturally over much of the US and grow a foot high, producing a quill of little brown tufts. It likes only 2 to 4 inches of water. Zones 6-11.
Cyperus species Umbrella Sedge
Description: These grasslike plants are topped with rufts of brownish flowers. You can grow the smaller ones in containers and enjoy them indoors in winter. Giant paprus or Egyptian paper reed (C. papyrus) is an African native that can grow 12 to 15 feet tall. Long thin leaves sprouting from the top look like green dust mops. It needs a huge container (20 gallon), lots of sun, and protection from wind. Dwarf papyrus (C. profiler, formerly C. isocladus), from South Africa, is only a foot tall. Grow it in 2 inches of water. Umbrella palm (C. alternifolius), from Madagascar, is sold as a houseplant and grows 1 to 3 feet tall; it has a daintier cultivar, 'Gracilis', and one with lengthwise strips, 'Variegatus'. It tolerates shade and thrives in 6 inches of water.
Zones 10-11 (C. profiler 9-10, C. alternifolius 9-11).
Equisetum species Horsetail
Description: These grasslike plants have jointed hollow stems and brown cones at the tip. Common horsetail (E. hyemale) is also called scouring rush. It usually grows 3 to 4 feet tail. Dwarf horsetail (E. scirpoides) may stop at 6 inches and is less hardy. Other species range to more than 6 feet. Grow them in containers in up to 8 inches of water or in a wetland area.
Eriophorum species Cotton Grass
A field of cotton grass looks almost surreal when it opens its 2-inch balls in midspring. The plant is about 18 inches tall; height doubles with the flowering spike. Two widespread and similar species are common cotton grass (E. angustifolium) and the aptly named broad-leaved cotton grass (E. latifolium).
Both will grow in up to inches of water in full sun but don't like hot summers. Zones 4-7
Houttuynia cordata Chameleon Plant
Description: Like many ground covers, this native of eastern Asia can be invasive, but it is useful for wet shade. Heart shaped leaves exude an orange scent if bruised. The true flowers are tiny yellow green knobs, with four white petal-like bracts (modified leaves). Look for the cultivar 'Chameleon', which has yellow and red mixed with the green on its leaves and is less invasive. Grow it in a container under 1 to 2 inches of water in sun or partial shade.
Iris ensata Japanese Iris
Description: Many people consider these the most beautiful of irises. These plants have been bred over centuries so that their standards have all but disappeared, but the almost horizontal falls are huge and often double. This makes them look somewhat flat, best viewed from above. The many selections, 2 to 3 feet tall and in almost every color but green, frequently bear Japanese names. They can grow in an inch of standing water and should not be allowed to dry out during the growing season. Zones 4-9
I. laevigata Rabbit-Ear Iris
Description: This Asian native is similar to the Japanese iris I its rather flattened flower, which is 2 to 3 inches across and lavender. Flowers are larger when grown in a few inches of water than when grown in moist soil. Cultivars are available in white and shades of violet, blue, or rose; one variety has variegated leaves. Soil for these also should be constantly wet but can be more alkaline then for other water irises.
Iris species Louisiana Hybrids
Description: You're more likely to find hybrids for sale than any of the species, which are becoming rare. The five species (I. brevicaulis, I. fulva, I. nelsonii, I. giganticaerulea, and I. hexagona) are always grouped together because they have the same habitat and requirements. Their flowers have no beards, and both species and hybrids tend to have drooping standards and narrow falls. Hybrids offer larger flowers than the species and are unusual among irises in the fact they come in reds as well as blues, purples, yellow, and white. They thrive in hot summers, but breeders have made them adaptable much farther north than the state for which they're named.
I. pseudacorus Yellow Flag
Description: It's hard to imagine this graceful perennial as a pest, but it has escaped and run roughshod over natives in the Mid-Atlantic states. As with all such plants, a gardener may end up loving it for its toughness or detesting it for its rambunctiousness. Yellow flag averages 3 feet tall, has ribbed gray-green leaves, and in early to midsummer bears 3 to 4 inches yellow flowers with slightly darker falls and brown or violet markings. It can grow in up to a foot of water.
I. sibirica Siberian Iris
Description: Even if you can't grow any other iris, you're bound to succeed with this elegant native of Central Europe and the former Soviet Union, which has graced gardens for 400 years. In May or June it bears small flowers of a dark, rich lavender-blue. Slender leaves up to 4 feet tall and narrow brown see heads continue to provide a punctuation mark after the flowers are gone. There are innumerable cultivars in many colors, including bicolors. Disease-free Siberian irises can survive with average moisture and go several years without being divided. While they bloom well in a few inches of water, they'll overwinter better if the pots are removed from the water at the end of the season and buried in well-drained garden soil until spring.
I. versicolor Blue Flag
Description: Native to the United States from New York to Texas, blue flag has dramatically narrow falls of lavender blue, each with a white splotch veined with purple. A few cultivars in other colors are available. Similar to yellow flag in shape but only 2 feet tall, it blooms in late spring or early summer. Unlike the other species described here, it doesn't grow in standing water.
Lysichiton americanus Western Skunk Cabbage
Description: Musky-smelling skunk cabbages are a favorite harbinger of spring. This western native produces rosettes of glossy, heavily textured leaves 2 to 4 feet long. A banana yellow spathe forms a vertical dish 16 inches long around a club (spadix) of tiny yellow-green flowers. It will tolerate moving water, but no deeper than an inch over its crown. It will also thrive in deep, rich, moist soil.
Lysimachia nummularia Moneywort, Creeping Jennie
Description: This central European creeper can grow in or out of the water; it usually ends up right on the edge. It has escaped into the wild in much of eastern North America. Moneywort has small round leaves and bears bright yellow, cup-shaped flowers with dark red spots. The yellow-leaved cultivar 'Aurea' is less likely to get out of bounds.
Mentha aquatica Winter Mint
Description: The leaves are much like those of dry-land mints, slightly hairy, serrated, and aromatic, and have reddish stems. In summer, tiny tubular lavender flowers appear in globes. Native to Eurasia, it will grow 3 feet high and wide and can be useful for stabilizing a bank, but like other mints in can gallop all over the garden. To keep it in bounds, give it a container in 6 inches of water.
Myriophyllum aquaticum Parrot's Feather
Description: This versatile plant from the Southern Hemisphere is sometimes categorized with submerged plants. But it will creep from the water's edge to make itself at home on a muddy bank; even in the middle of a pond, it waves its brushy whorls of blue-green leaves high above the water surface. The under water leaves are yellow-green, and its stems can grow up to 5 feet long. It can sometimes overwinter beneath the ice in frozen ponds north of its usual hardiness range.
Orontium aquaticum Golden Club
Description: "Odd but endearing" describes this flower, a 7inch skinny white spadix tipped with yellow, like a miniature club or poker, blooming from late spring to midsummer. Its 18 inch lance shaped leaves are blue-green and velvety. You can plant it as deep as 12 inches under water or on a muddy bank.
Peltandra species Arrow Arum
Description: These native marsh dwellers can become invasive, but it's hard to resist their arrowhead-shaped foliage. White arrow arum (P. sagittifolia) has white spathes that open wide, followed by red berries. Green arrow arum (P. sagittifolia) has white spathes that open wide, followed by red berries. Green arrow arum (P. virginica) is twice as big, at 3 feet tall, and produces green, nearly closed spathes and green berries. Grow them in containers in up to 8 inches of water.
Zones 7-11 (P. sagittifolia), 5-9 (P. virginica)
Pontederia cordata Pickerel Weed
Description: If you love blue flowers, you'll want to have several plants of this wonderful native growing on the edges of your pond. Its tiny baby blue flowers are clustered on spikes up to 6 inches long, blooming from late spring to autumn. Plants can grow to more than 4 feet tall and spread to 2 feet and offer shiny, upright, lance shaped leaves. Grow it successfully in full sun in water up to 5 inches deep or along the sides of a wetland garden or pond.
Sagittaria species Arrowhead, Swamp Potato
Description: These plants have even more dramatically arrow shaped leaves than arrow arums and look poised to be shot into space. Three petaled white flowers have yellow centers. A common native is the vigorous duck potato (S. latifolia), which grows 11/2 to 3 feet tall and offers 11/2 inch flowers and variously shaped leaves 4 to 12 inches long. Waterfowl love to snack on its walnut size tubers. Zones 4-11
Also native is the smaller flowered awl-leaf arrowhead (S. subulata), which is 2 feet tall and has 3-foot submerged leaves and egg shaped floating leaves. Zones 5-11
Japanese arrowhead (S. sagittifolia) has 18 inch leaves and purple blotches flowers on 3 foot stems, but it can spread too eagerly; its double-flowering from, 'Flora Pleno', is better behaved. Zones 5-11.
Giant arrowhead (S. montevidensis), a tropical species, reaches to 30 inches; they are marked with red at the base of each petal. Zones 9-11.
Saururus cernuus Lizard's Tail
Description: Despite the common name, the spikes of tiny fragrant white flowers look more like big caterpillars standing on end. One fan compares them to swans necks. A southeastern U.S. native, it grows 1 to 2 feet tall and has bright green, heart shaped leaves. The species name means "nodding"; if you give lizard's tail moisture and shade, it will reward you by romping about and producing hundreds of these bobbing "tails" more than 6 inches long.
Thalia dealbata Hardy Canna
Description: This plant will be the show piece of a water garden when it puts up its long fishing pole flower stalks topped with 8 inch panicles of violet flowers. The leaves grow on stalks, too, and are handsome in their own right; oval or more lance shaped, 20 inches long, and gray green with a white powdery coating. Sometimes called hardy canna, the plant can reach 10 feet tall and spread 6 feet wide. Give it an appropriately large container (at least 5 gallon) and grow it in 6 inches of water along the margin of a sunny pond.
Symplocarpus foetidus Eastern Skunk Cabbage
Description: This eastern skunk cabbage has a purple brown spathe, fatter than that of its western counterpart, enveloping the spadix like a monk's hood. The flower generates heat to protect it when it emerges from pond side ice or snow as early as February. Despite its name, it only smells unpleasant if you handle it. The "cabbage leaves" emerge when the flower is gone. Give it a bog or shallow water.
Typha species Cattail
Description: Cattails are aggressive, but their flower spikes and long pointed leaves are invaluable for waterfowl. Two common native species are narrow leaved cattail (T. angustifolia), which grows to 5 feet tall, and common cattail (T. latifolia), which reaches 10 feet. Both can be planted in water 6 to 12 inches deep and need at least a half day of sun. A variegated form of T. latifolia with stripes, called 'Variegata', is less vigorous and half as tall. Graceful cattail (T. laxmanii) has narrow leaves and grows 4 feet tall. The male 9tan) and female (dark brown) "tails" are separated on its stem. Zones 3-11
Dwarf cattail (T. minima) is less than 2 feet tall. Its leaves are slender and it's spikes are short. It can take lots of water but likes full sun. Flowers may be non-existent in warm climates. Zones 4-9.
Reference: Complete Home Gardening by: Miranda Smith
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