Rain Gardens: Combining Beauty with Function

The purpose of a rain garden isn’t limited to what grows in it. It is a landscape area that functions as a small-scale, temporary wetland.

A rain garden consists of a shallow depression that is planted with shrubs, flowers and grasses that are native to a region. Also called a bio-retention area, the rain garden’s saucer-like shape and water tolerant native plants, help precipitation absorb into the ground. It is not a retention pond, which can become a breeding area for mosquitoes. A rain garden is designed to hold water above ground for only a short while, as it filters down into the soil, making it a good landscaping choice for low-lying, often soggy problem areas in many yards. These planting beds work to manage excessive rainfall.

Rainwater itself, usually isn’t the problem, storm water runoff is. By allowing the runoff to be absorbed into a rain garden, the amount of pollution and sediment reaching creeks, streams and rivers can be significantly reduced. The gardens offer an earth friendly, attractive alternative to piping rainwater to the nearest sewer.

Native plants are recommended for rain gardens because they adapt to both extreme dry and extreme wet conditions. These plants take up excess water flowing into the rain garden, and standing water is only present for a limited amount of time. The water filters through both soil layers and root systems, before entering the groundwater system, which enhances infiltration, moisture redistribution and provides habitat for microbial populations involved in bio-filtration. Also, through the process of transpiration, rain garden plants return water into the atmosphere and provide a local cooling effect. Rain gardens can contain many different mixes of wildflowers, sedges, rushes, ferns, shrubs and small trees. Plants from a local nursery are well adapted locally, and are usually the safest to use in the long run. It is important to determine where the plants came from before purchasing them. Were the plants wild-collected or were they propagated at the nursery? Collecting plants in the wild can devastate local plant populations, so insist on plants propagated from division, cuttings or seeds. Additionally, propagated plants tend to be healthier than wild-collected plants making them better for the rain garden.

  • It is recommended that the garden bed be built with a planting mix of sand (25-35%), compost (50% or more) and native soil (15-25%). For a small rain garden, variations of these proportions may be workable.
  • Stabilize the top of the garden with natural mulch, 2-3 inches deep. The mulch acts as a sponge to capture heavy metals, oils and grease. Bacteria break down the pollutants as the mulch decays. The mulch also reduces weeds and maintenance.
  • Select natural mulch such as aged, shredded hardwood bark that will gradually decompose, adding compost (humus) to the soil. Apply the mulch to a depth of 2-4 inches and replenish as needed.

Ask your local nursery for plant, tree and shrub suggestions. It may be a good idea to do a sketch, to scale, of the rain garden area before going to the nursery to purchase your plantings.

A rain garden gives you an opportunity to make the most of every rainy day. Rather than allowing rainwater runoff to flow into the sewer, why not capture this valuable resource in your own beautiful and functional rain garden?

For more information on Michigan native plant material, you can read more HERE

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