Residents of the Okanagan Valley are increasingly aware that we can no longer view our water supply as an unlimited, cheap resource that we take for granted. As well, recent flooding events in Australia and elsewhere have forced us to recognize that water can have a destructive force. However, there are environmentally-friendly and positive approaches that can be implemented by individual homeowners to help reduce and treat storm-water runoff, increase wildlife habitat and beautify yards. One of these approaches is the rain garden.
The idea of rain gardens started in the state of Maryland in the late ‘80s and has expanded into one of the fastest growing areas of interest in home landscape. Rain gardens provide the homeowner with the opportunity to have a beautiful, low-maintenance landscape that helps manage runoff as well as increase biodiversity. By collecting and using the rainwater and snow melt that would otherwise run off one’s yard, rain gardens allow the homeowner to have a beautiful landscape with less watering.
The rain garden is a planted depression that is designed to use excess rainwater run-off from impervious surfaces (such as your roof and driveway). Rain gardens optimize the value of any rain that falls and reduce peak storm flows, which helps to reduce stream bank erosion and lower the risk for local flooding. Mown turf or grass areas are not as effective at soaking up and trapping excess run-off or in dealing with pollutants or contaminants in the water.
Rain gardens are largely composed of flowering perennials and grasses, together with scattered shrubs – an ideal mix for increasing the wildlife and habitat value of your landscape. You can increase the habitat value of your garden by increasing the diversity or complexity of the planting. Native plants tend to do well in rain gardens. If you replace paved surfaces or intensively managed grass areas with mixed naturalistic plantings, you will reduce the need for maintenance, as well as reduce inputs of fertilizer, water and energy.
The construction of a rain garden is relatively straightforward and simply involves lowering the level of the ground so that a rain-collecting basin is formed. Typically, the depth of a rain garden is 10-20 cm with gently sloping sides. The size of the rain garden is determined by the size of the drainage area and your soil type. The soil in the rain garden is ideally 50-60 per cent sand, 20-30 per cent topsoil, and 20-30 per cent compost. This mix prevents the run-off from standing more than 48 hours so that mosquitoes cannot complete their breeding cycle.
Rain gardens should be located at least 10 feet from house foundations and not on top of a septic system. Locating them in full or partial sun will enable a greater diversity of plants and promote evaporation of collected water. Sites with more than a 12 per cent slope are not suitable. A dry creek-bed or corrugated drain pipe can be used to carry rain from a downspout to the garden. It is important to establish a grass or groundcover border along the upper edge of the garden to slow down run-off water as it enters the garden.
Select and plant hardy, drought-tolerant plants and ornamental grasses. Once the plants are in place, mulch with dense materials such as shredded wood or wood chips (they need to be heavy enough to not float away). Provide an overflow path for excess water, which should be stabilized with hardy grass or groundcovers.
For more detailed information, check www.cleanwatercampaign.com or Rain Gardens by Nigel Dunnett and Andy Clayden.
This week’s column is written by Judy Baumbrough on behalf of the Communities in Bloom Committee.
