Build a Rain Garden

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Robyn Griggs Lawrence thumbnailIn many urban areas, the proliferation of impervious surfaces and poisonous runoff has pushed storm drainage--systems designed to channel rain overflow to holding ponds via drains and culverts, which then empty into fresh-water supplies—to its limits. To help restore natural drainage patterns, people in cities across the country are planting rain gardens. Created in depressions in yards and along roadsides, rain gardens (also called “bioretention” areas) include plants—usually native—that catch and divert runoff into the ground before it reaches storm drains and filter contaminants. In “Reduce Stormwater Runoff with a Rain Garden,” Natural Home & Garden gives you the step-by-step instructions you need to make your own rain garden—and be a part of the solution.

Build a Rain Garden in 10 Steps 

Materials 

Shovel
Ruler, stick or scrap wood (12 inches or longer)
Pencil or marker
Peat or compost
Moisture-loving native plants (see'Selecting Native Plants')
Shredded mulch
Decorative rock

Step 1: Contact your local utilities providers (electricity, gas, phone) to have them mark the location of underground wires or cables before you dig.

Step 2: Pick a location. A rain garden should be at least 10 feet from foundations, septic systems, utility lines and fence posts. You may wish to extend a downspout to reach the rain garden.

Step 3: Measure drainage rate. Dig a hole about the size of a large coffee can. Insert a ruler or stick into the hole. Fill the hole with water from a hose and mark the water level on the ruler. Wait four hours, then measure and mark the water level again. To determine the daily percolation, take the amount that has drained in four hours and multiply that by six. (Follow this formula: __ inches every 4 hours x 6 = __ inches every 24 hours). Your rain garden should empty within 24 hours, so if you can drain 6 inches in that much time, dig 6 inches down. If the water in your test hole doesn’t drain well, consider different placement, or add gravel, compost, sand or peat (see Step 7).

Step 4: Determine the garden’s depth. It should be no more than 6 to 8 inches deeper than the surrounding soil, but you can place it in the bottom of a larger landscape depression or slope.

Step 5: Outline the garden location. Use string and wooden stakes or a garden hose to mark the general placement. Think about the land’s slope and where heavy rain may come in and flow out; don’t orient the garden so that overflow runs into your foundation or septic system.

Step 6: Dig in. The depression should be within your marked outline and to the depth you determined in the previous steps.

Step 7: Check the drainage rate again. Fill the depression with water, then measure the rate as in Step 3. If the drainage is poor, remove 3 to 4 more inches of soil and till in some sand, gravel, peat or compost to a depth of 1 foot, then check drainage again.

Step 8: Add vegetation. Put plants that can tolerate “wet feet” in the lowest places. Lightly cover with additional soil if necessary, but don’t fill the depression completely.

Step 9: Mulch to keep the weeds out.

Step 10: Water. Until the plants are established—especially if rain is scarce—water to 1 inch at least once a week. If the depression gives regular overflow, you may wish to enlarge it or build a series of rain gardens with connecting drainage notches.

 rain garden 

This Wisconsin rain garden ends at a stormwater culvert. Photo by Jim Lorman