April 14th, 2008

How To Tuesday: Build a Rain Garden

Posted by Jason Pelletier, Low Impact Living

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Every time it rains, water runs off of your house, yard and paving. That water will eventually end up in rivers, lakes or oceans, and on its journey it can pick up a variety of pollutants ranging from fertilizer-based nutrients to trash to animal waste. What starts as clean rainwater can end up a toxic soup that contaminates our waterways and harms both people and wildlife (you can read more on this topic here).

Rain gardens are a great and beautiful way to reduce this problem. What exactly is a rain garden, you might ask? Well, it’s pretty much the same as a regular garden, with several key differences:

– It is slightly depressed, so that it can fill up with water during a rain storm;
– It contains plants that can deal with being “soaked” every once in awhile;
– It is strategically located to intercept water coming from your property, and
– It is specially designed to drain any stored water over a several day period.

If designed correctly, a rain garden can beautify your yard AND nearly eliminate your contribution to polluted runoff. Here are some simple steps to trying one of your own (or click here to find landscaping professionals who can help design and build your project):

1. Determine the size of the area from which you’ll intercept runoff. Determine the size of hard-surfaced area (roof, driveway, etc) that will drain to your rain garden. Remember that your roof drains through downspouts, so only count that portion of a roof where the gutters can be conducted to your garden.
2. Pick a location that is on the downhill side of your property where water is likely to flow into. Make sure it isn’t near foundations or on a hillside, as underground water can cause problems. And, watch out for utilities.
3. Determine your soil type. The three main categories you should look for are sandy soil, loam, or clayey soil. For more information on how to figure out your soil type, click on this link from HGTV.
4. Figure out the rain garden size. Any size rain garden will help, but ideally you will size it to hold all runoff from the area you measured above. To do this, simply multiply the area you measured by 20% if you have sandy soil, 30% if you have loam, or 50% if you have soils with lots of clay. Sandy soils will drain fast and thus need less surface area, while clayey soils drain very slowly and will need to store more water.
5. Create a design. Now the fun part begins! Put your latent landscape design skills to work and sketch out your garden. We find that using a piece of graph paper helps to get the measurements right. This link shows a number of rain garden designs - the plants are specific to the Mid-Atlantic region, but the designs can work anywhere.
6. Choose plants. Plants native to your region, and especially those that are intended for areas with wetter soils, are perfect for rain gardens. This is because they are already adapted to your climate conditions. We’ve organized some resources that list rain garden plants for different regions here.
7. Lay out garden. Using your design, stake out your garden and get ready to dig!
8. Dig the garden. At a minimum, dig your garden so that it is approximately 8” deep in the middle. Mix 2-3” of compost into the remaining soil. If you find that your soils are compacted (generally true if you’re having trouble digging them!), or if you have heavy clay soils, then dig another foot of soil out as well. Discard or move this soil and replace with sand (50%), topsoil (25%) and compost (25%), and put it back in the hole.
9. Plant. Lay out your plants according to your design, and then plant them.
10. Mulch. Mulch is the wonder material for any garden, and especially so for rain gardens. It keeps moisture in, weeds out, and your plants nice and cozy. Put 3-4” of mulch on top of your soil, making sure to leave a small circle bare around all of your plants.
11. Water. Your plants will need water to get established. If it doesn’t rain, water your plants at least twice a week for a month or so. Remember to water deeply so that your plants develop a healthy, deep root system.
12. Arrange downspouts. Now, you have to make sure water gets from where it falls to your rain garden. Arrange your downspouts so that they flow to your rain garden. If it is far, or to deal with path or driveway runoff, you might want to dig a small trench and fill it with either gravel or a pipe to conduct water into your garden. With some creative landscaping, you can make this small trench appear to be the tiny riverbed that it is!
13. Enjoy! Your new rain garden should now give you years of beauty and peace of mind knowing that you’re helping your local waterways. With any luck, your garden will turn into a buzzing centerpiece that attracts animals and your neighbors alike!

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