Hang on to Your Rain!

Bill Devlin
Adams County Master Gardener

(1/12) Last week I used this space talk about Chesapeake Bay-wise landscaping, which involves techniques used to keep pollutants - especially nitrogen, phosphorous and sediment - out of local streams and the Chesapeake Bay. Perhaps you have looked around Adams County and seen some examples of landscaping techniques meant to hold water and pollutants in place on farms, on commercial or government properties, or alongside someone's home. Maybe you have even added features to your landscaping that accomplish this, not even realizing you are holding water in your yard. Rain gardens are being built around the county.

But why would someone want a rain garden as part of their landscaping? There are several answers to this. Consider the fact that water remaining in your yard instead of running off becomes ground water, decreasing the need for watering the lawn. Water soaking into the ground can hold pollutants, and some of the soil microorganisms can begin to detoxify some of them. A rain garden with native plants can attract pollinators and other beneficial insects, along with other wildlife. A well-planned and executed rain garden can be aesthetically pleasing and relatively easy to maintain once established.

If you decide a rain garden is for you, now is a good time to begin planning. Rain gardens are best placed where they can intercept the water flowing off your property. As winter rains and snow melt, it is easy to see where water flows and where it puddles on your property. Be sure you chose an area away from your house and outbuildings. If the idea is to hold water, you don't want the water seeping into your basement.

Start the design phase by making a detailed, scale drawing of your yard. The shape of your garden will be up to you to some extent, but it must be able to catch and hold water. If you are building it on a flat piece of ground, you need to dig out a bowl-shaped area. If you are building on a slope, you need to build a berm on the downhill side capable of holding six inches of water in place. The size of your garden is based on the surface area that will drain toward it. Will the garden catch water from just your roof? Will it also catch water from impervious walkways and patios? Estimate the surface area which will contribute water to your garden and multiply this number by 0.12 to determine the minimum size of a rain garden to catch one inch of rain. (from Amanda Rockler, et al., 2016, Rain Gardens Help Protect Streams and the Chesapeake Bay, Rain Garden Fact Sheet 0371, UMD Extension) If you have clay soils, you may need a larger garden.

Using tracing paper, play with shapes and various locations for your garden. Move things, change the shapes, let your imagination take over. Then think about how to shape the 'bowl,' or catchment area. Once you decide on a good area for the garden, dig a test hole to see how well the water drains. Fill your hole - two feet deep and a foot wide - with water, let it drain completely. Within 12 hours refill the hole and see that it drains in less than 36 hours. When soil contains a lot of clay, amending it with organic matter and compost is recommended, but a rain garden in soil that drains very poorly might need the help of a specialist. Getting a soil test from the Penn State Extension will tell you how you soil needs to be amended.

As you determine what plants you want in your garden, consider that native plants are best for rain gardens for several reasons. They will be able to tolerate wet soil, but their extensive roots systems enable them to weather occasional dry spells. When choosing the plants, make selections based on your preferences, but don't forget the plants' preferences. The more water tolerant plants should be placed closer to the bowl of the garden, while plants that like drier soil should be placed on the rim or uphill side. Don't forget to think about shade and sun requirements for your plants. Using shrubs and grasses as well as perennials makes the visual appearance more interesting, and attracts a greater variety of insects, birds and other wildlife. Visiting established rain gardens will help you get an idea of how plants look and work together. Since it is January, it is a good time to read about rain gardens in books and on-line (search for Bay wise landscaping; University of Maryland Extension has great resources).

Read other articles on garden and landscape design