A rain garden uses native plants
and landscaping to soak up rain water (stormwater) that
flows from downspouts or simply flows over land during a
rain event. The center of the rain garden holds several
inches of water, allowing the stormwater to slowly seep
into the ground instead of flow directly from your roof,
yard or driveway into the nearest storm drain, creek or
Creating a Rain Garden:
- A rain garden allows 30% more
water to seep into the ground than a conventional lawn
(south River Federation & Center for Watershed Protection,
2002). This increase helps replenish the groundwater supply
(Important during a drought!), and also helps hold back
stormwater from contributing to the stormwater and sewage
overflows into nearby creeks and rivers.
- A rain garden reduces the amount
of water pollution that would otherwise eventually reach
the streams and rivers through stormwater runoff. Scientific
studies have demonstrated that the first inch of rainfall
is responsible for the bulk of the pollutants in stormwater
runoff. A rain garden is designed to temporarily hold
this one inch of rainfall and slowly filter out many of
the common pollutants in the water, such as oil, grease
and animal waste, that would otherwise flow into the waterways
via the nearest storm drain or stormwater runoff.
- The native plants used in rain gardens
require less water and less fertilizer than conventional lawns.
They also require less maintenance and provide habitat for birds
and other wildlife.
Instructions for Building a Rain Garden:
Before starting this project, please conduct
an Infiltration Test to determine if your soil conditions are
adequate for a rain garden.
- Plants for the garden
- Hose, rope or string
- Shovel or spade
- Measuring tape
- Humus or other soil amendments
- Downspout extension
Step 1. Size and Locate your Rain Garden:
- First, measure the footprint of your
house by getting the area (length x width) of your house and
then determine how much of your rooftop area drains to the downspout
you are disconnecting to your garden (for gutters with a downspout
at each end, assume that half the water goes to each downspout).
Refer to the sizing example (below) for guidance. Be sure you
measure the house footprint only, but include the area of any
driveway or patio areas that will drain to the rain garden (do
not take the roof slope into account). The surface area of your
rain garden should be between 20% and 30% of the roof area that
will drain into the rain garden.
- Locate the garden at least 10 feet away
from your house and your neighbors house (to prevent water
leakage), and create the garden in the lowest point of this
section of your lawn, maintaining a minimum 1% slope from the
house down to the rain garden. If your yard drain is also located
in this section of the lawn, you can build the rain garden around
the drain. The bottom of the rain garden would be a few inches
lower than the drain and the overflow would actually be in the
middle of the rain garden.
- If you are not building around the yard
drain, it is imperative that the overflow is safely conveyed
to a drain nearby to prevent it from flowing into your neighbors
property. Make sure the drain is in a suitable location in relation
to the rain garden in order to effectively manage the gardens
overflow runoff before it reaches the rain garden.
- When finding the right spot for your
rain garden, keep in mind that you will want to create a shallow
ditch or swale that carries the stormwater runoff from the disconnected
downspout to the rain garden. The swale will help slow the runoff
before it reaches the rain garden.
- Finally, lay out the boundary of the
garden with a rope.
Step 2. Dig the Rain Garden:
- To enable the rain garden to hold several
inches of water during a storm, youll have to dig a hole
3 to 4 inches deep across the entire surface of the rain garden.
If the soil lacks organic material, you can improve it by digging
the hole 5 to 6 inches deep, and adding 2 to 3 inches of humus
or other organic material. Make sure the bottom is level, but
gently slopes from the bottom to the ground level around the
edges. If the drop at the edge is too steep, you might get some
erosion around the edges.
- Next, test how the garden will hold
water during a storm by letting water flow into the rain garden
from a hose placed at the downspout. Based on this test, make
any necessary adjustments (e.g., create a berm on the lower
side of the garden using the diggingsthe soil that was
Step 3. Add Plants to the Rain Garden:
- Choose native plants that wont
require much watering, but make sure they can withstand wet
soils for up to 24 hours. (Refer to the list of native plants
- Also, take into account how much sun
your garden receives. Its often helpful to draw out a
planting plan before you start, and mark planting areas within
the garden with string. After planting, weeding may be required
until the plants become established. You may also need to periodically
prune some of the plants to let others grow. In the winter,
leave dead or dormant plants standing and cut back in the spring.
- Your garden may need a bit more maintenance
than a lawn in the beginning, but in the long run it will be
easier to care for and provide many added benefits!
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