If you're planning on building your own rain garden, here is a brief guideline to make sure it's done correctly, soaks up water properly, and is a thing of beauty and a joy to behold for many years to come. As with many projects, there are pitfalls to avoid, so best to do your research and consult professionals when needed. (No one needs a cesspool or mosquito breeding ground in their yard.) Click on images for larger version Newly planted garden (Photo credit: Windfall Ecology Centre)
Call before you dig!
As always, if you're digging in your yard, please call your local "Call before you dig" hotline. They will visit your property, mark out utilities, and give you a map to make sure you don't hit any utility pipes or wires. Find your number here: Call before you dig!
Get professional help
The information listed here is only a guideline and should not be used as a replacement for professional landscaping advice. Consult a professional landscape architect with training in rain garden design and ensure any installer you hire is licensed and familiar with rain garden installation. Rusty Schmidt, of Metro Blooms, presenting "Landscaping with Rain gardens" (Photo credit: Liz Cooper)
Location, location, location
Rain gardens should be downgrade and a minimum of 10 ft away from any building foundation (including the neighbours'). (Photo credit University of Wisconsin Extension)
Contours can help trap water on a slope
Take advantage of the natural slope by cutting your rain garden into it. Use the excavated soil to create a berm on the downward side. Make sure the top of the berm is slightly lower in elevation than the upper side to provide an outlet in the event the garden overflows. Rain garden slope (Photocredit: University of Nebraska - Lincoln Extenstion)
Getting the water to your rain garden
Water from roofs or paved surfaces can be directed towards the garden with a downspout extension, o-pipe, french drain or dry creek bed. Maintain a slope to ensure water does not collect and freeze en route. This way the garden should continue to work throughout multiple freezes and thaws all winter. Down spout directed into garden (Photo credit: Hearthmakers Energy Cooperative).
Test your soil, consider percolation rate
Before construction begins, it's important to test the infiltration rate of your soil. When the test pit (and rain garden) is completely saturated, it must still absorb all the water within 48 hours. If the soil is sandy and the infiltration rate is high, the rain garden can be smaller in area but deeper (up to 12" deep), as the water will soak into the ground quickly. If the soil is clay-like and the infiltration rates are low, the rain garden needs to be larger (twice the size) in area and shallower in depth (only 6" deep), given the same amount of water more area to soak in. Infiltration test (Photo credit: Sharyn Inward)
Size it right, well draining soil
Your rain garden should be able to handle 1" rain event from all the areas that drain towards it. If you have well draining, sandy or loam soil, your rain garden should be 12" deep x one twelfth (8.4 percent) of the areas draining toward it. (For example if the area draining towards the garden is 1000 sq.ft., the garden should be a minimum of 12" deep x 84 ft. sq. in area) Sandy soil (Photo credit: Eco-Scape Groundskeeping)
Size it right, clay or slow draining soil
Your rain garden should be able to handle 1" rain event from all the areas that drain towards it. If your soil is clay type, it needs to be 6" deep x one sixth (16.8 percent) of the areas draining toward it. (For example if the area draining towards the garden is 1000 sq.ft, the garden should be minimally (6" deep x 168 ft sq. in area) Clay soil (Photo credit: How to plant a Palm Tree)
Select native plants that are both flood and drought resistant
The plants located in the centre of the garden, where the water will pool during a downpour, should be able to withstand flooding, but also need to tolerate extreme drought, as your garden will dry up when it's not raining. Whenever possible, select species native to your region. Long-rooted, tall grass prairie plants work best, as their very long root systems can channel water down 9 ft or more (well below the footings of most buildings). Those same roots also make the garden more drought tolerant. Prairie grass diagram (Photo credit: Metroblooms)
Planting your rain garden
Plant tallest plants that can withstand flooding in the bowl of the garden. Plant species that can not tolerate standing water towards the outside of your garden. Adding a thin layer of compost is always a good idea. Reinforce any steep berms with natural coir matting that will biodegrade over time (Once established the plants themselves will hold the berm in place). Mulch with double-shred hardwood mulch to retain moisture and repress weeds. (Never use a filter medium in the bowl of a rain garden as it will inhibit the expansion of root systems.) Rain garden planting zones (Photo credit: Rain garden Handbook for Western Washington Homeowners)
Maintain your rain garden
During the first growing season, you'll need to ensure the plants receive adequate water until they become established. Some weeding will be necessary during the first few seasons. If you've planted native species appropriate for your soil, flooding and drought conditions, your rain garden will need very little maintenance once established. Garden maintenance (Photo Credit: REEP Green Solutions)