RAIN GARDENS FOR THE NORTH
Dr. Leonard Perry, Extension Professor
University of Vermont
If youíre like me, when you first heard of ďrain gardensĒ you thought of gardening in the rain, or some tropical rain forest. Rain gardens actually are slightly sunken gardens, usually with native plants, whose purpose is to collect rain run-off. These ďbioretentionĒ gardens are easy to create, fit into odd shapes in most landscapes, and are easily maintained.
Up to 70 percent of pollution in our above-ground waterways comes there from storm water. About half this storm water, especially in urban areas, comes from landscapes and building roofs. Collect even some of this in your yard, in a rain garden, and youíll be helping the environment. You donít need a large surface area for collecting rain, or a large garden, to make a difference. Any size rain garden helps.
Since the idea of your rain garden is to hold large surges of water, then let it seep slowly into the soil instead of running off your property, place such a garden in low spots where water already collects. It should be near drain spouts, but not too near buildings to avoid water seeping into basements. Beware of underground utilities if excavating. But, if digging, donít do so under trees or you may seriously damage tree roots. Rain gardens donít need to be deep, only six inches being sufficient in many cases. Keep the bottoms flat to help disperse the water more evenly.
Since the water from a rain garden should seep slowly into the surrounding soil, soil type is important. You donít want clay soil that will merely hold the water. If your soil is even light clay, you should replace it for your rain garden. Merely adding sand to a clay soil likely will not help. Sandy or gravely soils are ideal. If replacing soil, you may need to do so to a depth of two feet.
Since this is a garden, and will remain dry much of the time when not raining, what about the plants? These not only help beautify a rain garden, but their roots create channels for water to infiltrate the soil. They absorb water, giving it off through their leaves.
You may use non-native plants, but native ones are particularly adapted to local conditions and often have deep roots. Youíll want plants that arenít too fussy, that will live in dry conditions and wet. One of my favorite plants for such conditions is the Siberian iris. Whatever plants you choose should be vigorous to establish easily, and have healthy root systems. Large plants will establish more quickly.
Some native herbaceous plants for northern rain gardens might include the Swamp Milkweed, New England Aster, Marsh Marigold, Cardinal Flower, Switchgrass, and Sensitive Fern. Woody plants might include Red Osier Dogwood, Elderberry, Winterbery, and Highbush Cranberry. Plants with invasive roots such as Ribbon Grass may work well if there is no chance such can wash into other waterways, escape into the wild, or take over other garden beds. Invasive plants spread by seeds such as Purple Loosestrife or Honeysuckle should not be used.
Once planted, keep plants well-watered as you would any garden plants if it doesnít rain sufficiently. If water flows into your rain garden from one or two main points, you may want to place some rocks there to break the strong water flow. This will prevent erosion of soil and mulch.
Finally, donít just leave this rain garden and assume it needs no care! It may need less care than other more intensely maintained beds, but still keep it weeded and plants divided as needed. If a plant isnít to your liking, or isnít thriving, donít be afraid to move or replace it. If more than rain flows into your garden, such as sediment and debris, remove it before drainage slows and plants are buried.
Follow these basic tips and youíre ready to begin your rain garden. If youíd like more details, such as calculating soil infiltration rates and the ideal size rain garden, there are some good web sites to visit, such as that of Rain Gardens of West Michigan (www.raingardens.org).
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