Is there a place in your yard where rainwater runoff concentrates and causes erosion? Construct a rain garden to control it. A rain garden will intercept the natural water flow, spread it out and slow it down, and allow it to gradually infiltrate back into the ground.
If you’re into sustainable gardening, you’ll appreciate the functionality of rain gardens. They work to preserve the water quality of our streams and lakes by filtering pollutants and reducing erosion. They also serve to recharge the groundwater. A rain garden can be an attractive addition to your yard, one that thrives without irrigation, requires less maintenance than a lawn, provides a succession of year-long color and texture interest, and attracts birds and butterflies – an environmental work horse that pleases the eye and soothes the soul.
Building your rain garden is easy. It makes a great project to help teach kids about the interactions of gardening and nature.
Tools you’ll need:
- a pick and shovel for digging
- a tarp and wheelbarrow for dirt control
Use the instructions below to help guide you in constructing your rain garden.
Locating Your Rain Garden
- It’s best to use water coming from your hard surfaces – your roof, driveway, and/or patio – to supply your garden.
- Where does the water exit these surface? Follow the water’s flow path to a spot that’s almost level or has a slight depression.
- Keep the rain garden away from building foundations, or areas where a high water table is within 24″ of the soil surface.
- And make sure you don’t build it on your septic tank or drain field, or on a steep slope.
- A gentle slope, however, is the perfect place to spot your garden.
Determin Your Rain Garden’s Drainage Area
- Size your garden based on the square footage of the area draining to it.
- Determine the drainage basin feeding your garden – any combination of surfaces (ground, paved, tiled or shingled) that directs water to your chosen garden area.
- Remember that water from your roof will exit at a downspout and then flow to your garden spot. Add the roof square footage that contributes to this downspout to the total drainage area for that particular garden spot.
- Once you have the size of your drainage area, you can size the actual garden.
Size Your Rain Garden
- Soil type is critical in sizing your garden properly.
- Clay soils infiltrate water slowly. Size rain gardens in clay soils at 60% of the drainage area.
- Sandy soils allow rapid infiltration. They can be 20% of the area.
- Depending on how fast water infiltrates into your soil, size loamy soils between 20% and 60% of the drainage area.
- If your rain garden exceeds 300 sq.ft., consult a professional garden designer or landscape architect for proper sizing.
Building Your Rain Garden
- Lay out the rain garden in a curvilinear pattern, using rope, a garden hose, sports field lime, or surveyor’s paint to define the shape.
- Use your pick and shovel to excavate soil so that the deepest part of your garden is 8-10″ deep.
- Place the dirt on your tarp to keep it off your grass and for easier handling.
- Level the garden’s bottom.
- Fill your wheelbarrow with dirt and roll it to the garden’s downhill side. You’ll build a dam here. The top of this dam should not be higher than the garden’s uphill side (about 12″).
- Your garden should hold no more than 6″ of water above the ground surface. Add an overflow path for water to take in case runoff from an extended rain exceeds the garden’s capacity.
- Mix 2″ to 4″ of organic compost into the soil in the bottom of the garden. The soil should have a neutral pH.
- Proper drainage is a must. If your soil has a high clay content, remove 1-2′ and replace with a mixture of 50-60% sand, 20-30% topsoil, and 20-30% compost.
- Plant a grass strip on the upper edge of the garden to slow down runoff.
- Stabilize the earth dam with grass.
- Use a mix of ornamental grasses, shrubs, and self-seeding perennials in your garden, both drought and moisture tolerant plants. Check with your county extension agent or a botanical garden in your area for plants suitable to your region.
- Tuck a 3″ layer of mulch around the plants. Use pine straw or shredded hardwood, as pine bark tends to float away.
- You can put down a layer of newspaper before you mulch to help control weeds, but don’t use a commercial weed barrier – they contribute to shallow root growth and matting within the mulch layer.
Rain Garden Maintenance
- Keep an eye out for weeds that get past your newspaper layer, and remove them promptly.
- Add mulch as needed. If the right plants are used, your rain garden will be relatively low maintenance.
- Deadhead perennials and cut them back according to the needs of the species.
- Shear ornamental grasses at the end of winter – they’ll easily recover, and be full and lush by summer.
Now all you have to do is sit back and enjoy the fruits of your labor.
A rain garden is a fine addition to any property, and following these guides will ensure that your rain garden functions properly and gives you pleasure for years to come.