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What is beautiful, prevents pollution, attracts butterflies and can help maintain groundwater
supplies? Rain gardens! Hello, this is John Pennington, county extension
agent for agriculture and water quality in Washington County, and today I’m going to
be talking about how to build a rain garden to protect water quality.
So, how do you build a rain garden? First, you need to find a good location. Building
the garden will be easiest on level ground or on a gentle slope.
The key is to capture stormwater runoff from impervious areas before it reaches a storm
drain inlet, waterway or any pollutants that may lie in between.
Build your garden at least 10 feet from buildings, so water soaking into the ground will not
damage the foundation of your house, patio or other structure, and you will need to avoid
areas where water already ponds, as the garden will not drain properly where percolation
is already restricted. Mark your potential area and call Arkansas
One Call at 811, also called “call before you dig”. Then perform a simple percolation
test by filling a 12-inch deep hole with water. If the water has not drained within 48 hours,
consider another location and repeat the process. Rain gardens can be most any size or shape,
but a good rule of thumb is to design the garden to be one-third of the size of area
that it drains. [Picture of various rain gardens and a drawing of a rain garden location drawn
on paper.] If the drainage area will require more than 300 square feet of rain garden,
consider splitting the stormwater flow into two gardens, or just consider capturing enough
flow for 300 square feet. The ideal depth of a rain garden is about eight inches deep
from the top of the berm to the planting bed. With the high clay content of many Arkansas
subsoils, the incorporation of organic matter and sand can improve the soil’s infiltration
rate and water–holding capacity. A few inches’ compost and sand can be added across the entire
garden area and mixed to amend the existing topsoil. If much of the topsoil was used to
build a berm around the garden, additional topsoil may also be necessary.
When choosing plants for your rain garden, it is essential to consider their ability
to flourish in both extreme wet and dry conditions. Native plants are good options, since they
have adapted over time to local climatic conditions and have survived through many wet periods
and droughts over time. Not to mention that they do not need pesticides or fertilizers
and provide habitat for honey bees and butterflies. A list of these potential plants that can
thrive in Arkansas rain gardens is listed at www.uaex.edu, and you can also contact
your local county extension office for a fact sheet about rain gardens and stormwater.
Once you have selected your plants and created a design, it is a good idea to set out all
of the plants to see how the whole garden will look. This way, you can make any needed
spacing adjustments before the plants are installed. If you had amended your soil with
layers of sand and compost, thoroughly mixing the materials in and around the planting holes
will ensure happy plants with happy roots. Once the plants are in, add several inches
of hardwood, cypress or rock mulch to help prevent erosion, conserve soil moisture and
reduce weeds and regulate soil temperatures. After planting, you’ll need to irrigate
the garden until the plant roots are well-established. Once established, the plants should only need
to be watered during extended periods of drought. Like most gardens, regular weeding will be
necessary, and count on leaf removal in the fall. Every now and then, a little shallow
excavating of soil that has washed into the garden may be necessary to maintain its water-holding
capacity. Applying a new layer of much each year, and thinning or replacing plants as
needed, will help maintain a beautiful appearance of your rain garden.
Now you know how to build a rain garden to protect water quality.
For more information about protecting water quality, contact your local county extension
office or watershed partnership. This podcast was funded by the Arkansas Natural Resource
Commission and Environmental Protection Agency.