Rain Garden Basics
Did you know that our aquifers, which provide many communities with water, are being depleted and one way of lessening this is through a rain garden. A rain garden collects water from nature and downspouts and allows it to slowly return back to the ground. This in turn replenishes the aquifers. While this sounds complicated, the process is really very simple and requires time, effort, and the desire to improve the environment.
While this all sound well and good, what are the advantages of a rain garden? First, it can reduce flooding by allowing the water to go into the ground verses the gutter. Second, the water that enters the aquifer is cleaned by Mother Nature’s washing machine called soil. Third, it can change a negative to positive in many landscape designs by turning a depression into a naturally functional garden with style. Lastly, a rain garden can be habitat for many birds, butterflies, and beneficial insects, which is very important for anyone who wants to garden organically. Have said that, the old belief that rain gardens attract mosquitoes is unfounded. Only the female mosquito drinks blood and lays eggs that require 7 to 14 days to hatch. The water in a well-designed rain garden will have already percolated down through the soil before the eggs have a chance to hatch. In doing so, mosquitoes are never a problem.
What you need for a rain garden generally is an area that has a slight depression. It also needs to be 10 feet from your home, 15 feet from a septic system, and not too wet. Before digging, one should call their local utility company so that they can come out and mark where their lines are located. Once that is done, you will need to dig a test hole that is 2 feet deep. This hole will be used to test the percolation of the soil. After the hole has been dug, pour 8 to 12 inches of water in the hole and time how long it takes the water to disappear.
To know if the area is proper for a rain garden, one must calculate the rate. This is done by taking the number of inches of water poured in the hole divided by the amount of time it took for the water to drain away. As an example, if you pour 8 inches of water in the hole and it takes 12 hours for the water to filter down through the soil, you would then take 8 divided by 12. This would give you 0.67, which can then be used to help you decide how deep the rain garden needs to be. If this number is 0.5 or larger, then the area will need to be 18 inches deep. If on the other hand, the number is smaller than 0.5, then the garden will need to be 30 inches deep.
If the area’s percolation rate is less than 0.1, do not create a rain garden on this space.
Once the area has been chosen, the next step is to play around with the shape of the garden. Using a gardening hose lay out possible shapes. Teardrops and oval are popular shapes but do not limit yourself to these design choices. Once you have a shape you like, trace it out on the ground using lawn paint. Remove the hose and repeat the shape 18 inches from your design. This simple step will prevent grass from invading your rain garden.
Now it is time to remove the sod. This can be done by hand or by machine. Once the sod has been removed, begin digging the garden. Remove enough soil from the garden space so that the garden is the appropriate depth. After that has been reached, create a berm that is at least 2 feet at the base and 1 foot across at the top. Pack the soil the soil down to keep it from falling back into the bed.
One this is done, the next step requires one to dig a trench for their rain gutter to go into. This trench will go all the way into the rain garden. Once the piping has been laid, stones can be place on top of the pipe inside the rain garden. After that is done, fill in the trench.
Next, fill in the rain garden with soil leaving 6 to 12 inches empty. But do not just add back the soil you dug up. Instead, for every 2 scoops of garden soil add 1 scoop of compost. This will help with drainage and provide nutrients for the plants that you will be planting. Also, do not just dump the soil in the hole. Gently slope the soil used for the filling. This will create a functional rain garden verse a pond.
After the garden has been filled in to the point described above, it is time to plant. Rain gardens have three plant zones. These are those who like wet feet, those who can tolerate wet soil but not standing water, and those that require dry soil.
Those that can tolerate standing water should be planted in the center and include rain iris (Zephyranthes species), crinam lily (Crinum species), goldenrod (Solidago rugosa), seashore mallow (Hibiscus moscheutos), and dwarf palmetto (Sabal minor). Plants that can tolerate some wet soil include Siberian iris (Iris sibirica), daylily (Hemerocalis hybrids), maiden grass (Miscanthus cultivars), and inkberry (Ilex slabra). These should be planted around the berm.
Those who like it dry include American holly (Ilex opaca), red bay (Persea borbonia), muhly grass (Muhlenbergia capillaries), verbena (Verbena Canadensis), willow oak (Quercus phellos), and southern magniolia (Magnolia grandiflora). These plants should be scattered in that 18 inch zone that was added to the design to prevent grass from invading the area.
Once the plants have been planted, add 3 inches of mulch. This will keep the weeds out while conserving soil moisture, which is very important for those who like wet feet. Also, until the plants become established and/or during times of drought, add water to the rain garden.
A rain garden is not maintenance free. In the spring, check the mulch level. If it is below that 3 inch mark, replenish with additional mulch. Also, remove any weeds as soon as they appear. Plants will also need to be divided and pruned to keep the rain garden looking its best.