REESER MANLEY

Local rain garden offers a lesson in native perennials for wet areas

The rain garden mid-May, between spring rains, when marsh marigolds are in full bloom and clumps of slender blueflag iris are sending up their grassy leaves.
The rain garden mid-May, between spring rains, when marsh marigolds are in full bloom and clumps of slender blueflag iris are sending up their grassy leaves.
Posted July 08, 2011, at 7:30 p.m.

Since early spring, I have made weekly visits to the rain garden at the University of Maine Cooperative Extension office in Ellsworth, chronicling with photographs the development

of native plants growing there, both woody and herbaceous. Now in its second year, this garden

absorbs a tremendous volume of water with each rainfall, water that otherwise would have flowed into storm drains and nearby surface waters, diminishing groundwater while enhancing

the potential for erosion, water pollution, and flooding.

The rain garden is a planted depression off one corner of the building. During each rainfall, water from the roof falls onto a gravel bed at the base of the building wall and is carried to the garden through perforated pipe buried in the gravel. Immediately after a rain, the garden is flooded, but within a short time, a few days at most, the standing water has drained into the surrounding ground and the clayey soil begins to dry. In mid-summer, this can be a very dry garden.

Some of the plants in this garden are old friends, including rhodora, a native rhododendron common to both seasonally flooded areas and arid granitic outcrops. Others, particularly the herbaceous perennials, I did not know well, or at all, until I started these weekly visits.

For example, while I have often encountered marsh marigolds (Caltha palustris) in the wild, in the shallow water of hardwood swamps, the Extension rain garden provided my first opportunity to observe them in a managed landscape. They were the first herbaceous plant to flower in this garden, thriving in the full sun of early spring, blooming in mid-May with waxy bright yellow flowers that took center stage for two weeks.

Bloom time for marsh marigolds overlapped the appearance of rhodora’s purple flowers and through most of May this dominant combination of bright yellow and purple was punctuated by the fresh green of emerging leaves belonging to Iris prismatica, the slender blueflag iris. By May 30, the rain garden was a sea of green, the rounded leaves of marsh marigolds, their flowers gone by, surrounded by broad clumps of slender sword-shaped iris leaves, 3 feet tall and

swaying in every gentle breeze.

Native to saltmarshes and wet near-coastal meadows and often found in the company of sweetgrass, wild rose and bayberry, slender blueflag thrives in seasonally-flooded gardens. It is

a rare iris in the wild of Maine, listed in our state as a threatened species due to habitat destruction (filling of wetlands) at the northern limit of its range, but common in other states and

still available from growers of native perennials.

The rain garden’s carpet of green continued to expand through early June and, by my visit on June 12, the slender blueflags had burst into bloom. And just in time, because the leaves of marsh marigolds (a summer-dormant perennial) were falling apart, edges curling as they turned to brown in the summer heat, and another player needed to take center stage. The iris flowers, blue-purple with heavily streaked falls, were still in flower on June 27.

Meanwhile, my most recent photographs, taken on June 27, show a clump of the swamp sunflower (Helianthus giganteus) waiting in the wings. Already 5 feet tall and buttressed with

stout stakes at all four corners, this towering sunflower will burst into bloom in late July and continue flowering into October, reaching a final height of up to 12 feet. The yellow flower heads, up to 3 inches in diameter, are borne at the top of each plant in loose multibranched clusters.

Another player in the late summer act will be the swamp milkweed (Asclepias incarnata)

with its tight clusters of pink to mauve flowers on plants up to six feet tall. The flowers are followed by seed pods (4 inches long), which split open at maturity releasing silky-haired seeds

on the wind. Butterflies use swamp milkweed as a nectar source while the foliage is a food

source for monarch butterfly larvae.

So far my weekly visits have taught me that a rain garden planted with only native plant species can be both functional and beautiful. I realize that these same native plant species can be grown in any seasonally-flooded landscape site, including the edges of pools and ponds that swell with snow melt and spring rain.

Note: All of these herbaceous perennials can be purchased from Peter and Julie Beckford, owners of Rebel Hill Farm in Clinton, Maine. It’s best to call ahead, 843-6916.

 

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