30 June 2011

How about a rain garden

Rain gardens are probably not what you think. They are not just holes in the ground that collect rainwater and they are not places where gardeners put water-loving, tropical plants. In addition, they are not mosquito havens.

Plants are made up of over 90% water and suffer when conditions prevent them from having the amount of water they need. Weather-wise, the amount of water our gardens receive from Mother Nature is a feast or famine situation.
Northeast Oklahoma receives an annual average of 44-inches of moisture and almost always has a month or two of drought conditions each gardening year. Rain gardens take advantage of both extremes in an ecological manner.

A rain garden is designed to capture and hold the water that naturally pours off your roof and flows across your yard. Several inches of amended soil in the rain garden basin holds the water for three days while it percolates into the ground. As an added ecological benefit, rain gardens clean pollutants out of the water as it percolates through.

Unlike agricultural ponds and industrial water retention basins, urban rain gardens are designed to be filled with garden plants. Too much water around the roots of plants can cause as many problems as too little, so the basin of a rain garden is dug to one-foot deep and then backfilled half the depth with improved soil.
To divert water from structures and to prevent the water from entering the septic or sewer system, a rain garden is located 10-to-20 feet away. The first step is to identify where rainwater flows and comes off roofs.

To make a rain garden a water-collection depression is created either by digging down or by berming a slope. To prevent mosquitoes, the garden bowl should drain in 1-to-3 days.

Rain garden in Grove OK
If a home has several places where water flows, there are design solutions such as directing the water by the use of French drain pipes, building up berms and digging out waterways called swales.

Once the garden is set up, it is time for plant selection. Perennial plants create a low maintenance garden but annuals can be used. All the plants must be able to tolerate wet and dry periods so supplemental water is not needed.

 Perennial grasses, native and non-invasive plants will require the least attention.  Avoid nitrogen fixing plants.

Trees for rain gardens include: Paw Paw (Asimina triloba) and Sweetbay magnolia (virginiana).  Perennial plants for a part sun rain garden include: Blue wild indigo (Baptisia), Iris and Woodland phlox (Phlox divaricata).
Shrubs for rain gardens in part sun include: Red chokeberry (Aronia arbutifolia), American beautyberry (Callicarpa Americana), Ozark witch hazel (Hamemelis virginiana), and Virginia sweetspire (Itea virginica).

Perennials for a sunny rain garden: Yarrow (Achillea millefolium), Feather reed grass (Calamagrostis acutifolora),  Joe-Pye Weed (Eupatorium purpureum), Rush (Juncus), and Penstemon.

The benefits of rain gardens are widely accepted and many states have established programs to encourage land owners to install them. 

Kansas City MO has an initiative to put in 10,000 residential rain gardens. Their advice is at http://tiny.cc/lwigw.

There is a Bioretention Cell Demonstration Project in Grove, OK, that is a good example of a rain garden on a natural slope.  At OSU’s http://lid.okstate.edu/bioretention-cells-and-rain-gardens  there are several links to recommended references.

Another Internet resource is Rain Garden Design at the Low Impact Development Center www.lowimpactdevelopment.org .

An award winning book by two horticulture professors has easy to follow instructions and tips. “Rain Gardening in the South: Ecologically Designed Gardens for Drought, Deluge and Everything in Between” by Helen Kraus and Anne Spafford, published 2009, by Eno Publishers (www.enopublishers.org). $15.

I sent the authors an email and Spafford answered my question. We live on a rocky hill and I asked if we could build a berm on the south side to hold rain water that floods across our yard, removing the mulch as it travels.

The soil on that hillside is only about 6-inches deep. It took about 4 years of digging and planting to get a native oak tree to survive. Spafford responded that yes, we could go that route so it will be our fall/winter project - AFTER these 100 degree temps recede and we can do something other than water, water, water.

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