How to Create a Rain Garden

Jenn Nawada heads to Portland, Oregon, to meet up with soil and water conservationist Kathy Shearin. Together, they help a couple revitalize their front yard’s water run-off by installing a rain garden with native plantings. Most homeowners love a big, green lawn around their homes.

However, those grass surfaces might as well be asphalt in rainy regions. Rainwater hits their surface and washes out to the street. There, it mixes with dirt, oil, and other waste before working its way back to streams and other water sources. That’s not an ideal use of water. A pair of homeowners decided to install a rain garden to prevent their northwest property from shedding more water than it should. Landscape contractor Jenn Nawada answered the call.

How to Create a Rain Garden

1. After choosing the area for the rain garden, start by performing your own percolation test. Dig a hole approximately 12 inches deep and around. Fill the hole with water and measure the height of the water. The water should drain at a rate of at least ½-inch per hour to make the site suitable for a rain garden.
2. Locate the downspout. If necessary, either disassemble the downspout with the screw gun or cut it with a hacksaw so you can install the downspout diverter elbows. Use self-tapping metal screws to attach the elbows.
3. Mark the outline of the rain garden on the ground. Following the shape of the outline, draw matching shapes inset around 12 inches from each side to mark the slope.
4. Starting in the center, use the shovel to excavate the soil from the rain garden. The center should be deepest and each subsequent section should be less deep.
5. Use the pickaxe and shovel to dig out a winding trench between the gutters and the rain garden.
6. Incorporate a 4-way soil mix into the excavated hole. Leave the soil compacted to allow the plants to root better and the water to drain.
7. Line the trench with waterproof landscape fabric and cut it roughly to shape and size. Pile river rock on top of the landscape fabric. River rock will never compact, allowing the water to run through it freely.
8. Plant the rain garden plants in the garden bed. Choose a mixture of deciduous and evergreen shrubs, trees, and groundcover plants to fill the space.
9. Place the sod excavated from the garden bed around the edge of the garden bed to help retain water.
10. Apply a thin layer of mulch to the top of the garden bed to retain moisture. Water through the summer months until the plants are established.

Resources

Jenn marks out the area of the rain garden using spray paint. Then Jenn, Kathy, and the homeowners use digging shovels to remove the sod and start digging the basin.

To install the downspout extension, Kathy cut the downspout with a hacksaw to the necessary measurement and capped the standpipe. She then attached an elbow to the downspout. Kathy then capped the downspout extension to the elbow.

To install the conveyance, Kathy, Jenn, and the homeowners used trenching shovels to dig a shallow trench about 6” in depth and 3-4” in diameter from the downspout to the rain garden’s basin. They then lined the entire stretch of the trench with pond liner. Finally, they Fill the trench with ¾’ – 1 ½” river rocks or “drain rock”.

Jenn, Kathy, and the homeowners incorporate a 4-way mix into the existing soil as they backfill the basin. Once the plants are installed, they then cover the surrounding area with Fine Hemlock mulch.

Expert assistance was provided by Kathy Shearin, Urban Lands Program Supervisor at East Multnomah Soil and Water Conservation District and by Drake’s 7 Dees Landscape Design.

Materials

• Downspout diverter
• Metal screws
• Marking paint
• Landscape fabric
• River rock
• 4-way soil mix
• Rain garden-friendly plants
• Hemlock mulch

Tools