There are few more valuable plants around the water garden than the marginals. These are the plants that make their homes in the transitional area between water and land. Most enjoy having “wet feet” without being too deeply submerged in water. Think of them as shallow-water plants.
Here are a few of our favorites for you to consider adding to your water garden.
PARROT'S FEATHER (Myriophyllum aquaticum) This plant's pink stems rise above silvery blue or lime-green foliage. Leaves are sparse underwater. However, about 6 inches above the surface, they grow into feathery whorls. Parrot's feather is good for trailing over the side of a container garden or alongside a waterfall. It is a fast-growing marginal plant and may need to be thinned occasionally to keep it in check. To survive cold winters, roots must be under ice. Plant their crowns 4 - 10 inches below the water surface. Parrot's feather likes full sun but tolerates partial shade. It is hardy in zones 3 - 11.
IRIS The marginal species of this popular garden plant include blue or wild flag iris (I. versicolor, with attractive blue, bearded flowers); rabbitear iris (I. laevigata, usually white with broad-petaled, beardless flowers); Louisiana iris (I. fulva, red to orange beardless blossoms); and Japanese water iris (I. ensata, with white, blue, purple, reddish-purple, and lavender-pink beardless blooms). Another, variety, yellow flag iris (I. pseudacorus, beardless), is especially easy to grow. I. laevigata 'Variegata' is popular for its striped leaves. All of these iris varieties make excellent marginal growers. Plant iris rhizomes (the fleshy, root-like portion) from 2 - 4 inches below the water surface in full sun to light shade. Iris are hardy perennials in zones 2 - 10, depending upon the species.
ARROWHEAD (Sagittaria spp.) This marginal is named for its arrowhead-shaped leaves that rise up 1 - 2 feet above the surface of the water on slender stems. Because of their leginess, the plant may tend to lean some. Three species are popular as garden-pool marginals: S. sagittifolia, S. latifolia, and S. japonica. Arrowhead blooms later than most other marginals, with white flowers emerging in summer. It is a North American native plant, an easy grower that does not transplant well. It prefers bog-like conditions. Plant its roots 1 - 5 inches beneath the water surface in full sun to partial shade. Plants are hardy in zones 4 - 10.
MARSH MARIGOLD (Caltha palustris) One of the most popular of marginals, marsh marigolds feature bright golden spring flowers that bloom above heart-shaped, shiny, dark green leaves for a month or more. The plants rise about 1 foot above the water and spread about 1 foot across. They go dormant by midsummer. Grow them near other marginals to ensure that the bare spots they leave during dormancy are hidden by neighboring foliage. Marsh marigolds are a good choice to plant in damp spots near a stream, and they grow well in bog gardens. They are native to North America. Plant them in full sun with the crowns no deeper than 2 inches below the surface of the water. Plants are hardy in zones 4 - 10.
CATTAIL (Typha spp.) The familiar brown flower heads of cattails are borne in late summer through early fall. Many species are too invasive to grow in garden pools except in pots, but there are some that can be planted without fear. For large water gardens, there's T. latifolia. T. laxmannii is suitable for gardens of medium size. The miniature cattail, T. minima, does fine in small garden ponds. Cattail plants can grow up to 6 feet tall or taller, depending on the species and growing conditions. Plant them so that their crowns are up to 6 inches below the water surface. The plants grow best in full sun to partial shade. Cattails are hardy in zones 2 - 10, depending upon the species.
CANNA (Canna) These magnificent bloomers send up stalks with brilliantly colored, electric flowers from 5 – 6 inches across. They grow in up to 4 inches of water and reach a height of 4 – 6 feet, making them ideal for strong backdrop plants or a splash of color mixed in with your cattails. Bulbs are readily available and inexpensive and can be treated as an annual in most locales. Plants are hardy in zones 9 – 11, although we have overwintered our pond cannas in zone 8.
PICKEREL (Pontederia cordata) The spade-shaped leaves of this plant reach 24 – 30 inches in height and are punctuated with spikes of vivid purple flowers, resembling the flower heads of grape hyacinth. The flower heads grow to 5 inches in length, providing a splashy show of color throughout late spring and early summer. The plants grow happily in up to 10 inches of water and hard hardy in zones 5 – 11.