By Kevin Brooks
Part II of this series discusses a rain garden and it’s benefits to reduce water costs. We’ll also cover the best plants to use in landscaping!
Rain Garden
Rain Garden
An alternate to this concrete box technology is a bioswale. A bioswale, sometimes also referred to as a rain garden, is simply a shallow depression or trough with a gentle slope, cut into the earth (swale) to collect the surface water and channel it to its desired location combined with biological filter media to treat the water. The biofilter media is simply selected plantings and organic material that is used to capture pollutants, such as silt and sediment, which contaminate water by increasing its turbidity. In addition, properly designed bioswales can be tailored to not only capture, but also treat chemical contaminants such as oils, as well as phosphates and nitrates – common fertilizer ingredients. Properly tailored plantings actually filter these toxins and utilize the excess nutrients. This treatment option gives the bioswale an advantage over the conventional sand and oil separator. Because these types of pollutants are common to parking areas, bioswales are commonly used for this application. A bioswale, or rain garden, collects surface water and channels it to its desired location. Roof gardens are a popular option to reduce surface water from collecting.
Bioswale plantings include primarily grasses, planted at the base of the swale, as well as on its sides. The grasses that are selected need to be tailored to the climate; in California for example, the grasses need to be drought resistant, while at the same time be accepting of being saturated for extended durations.
In addition to a base layer of grasses, woody stemmed plants and shrubs, and even in some cases trees, are also used for bioswales. Plants and shrubs are used not only out of aesthetic considerations, adding contrasting profiles and colors to the grasses, but also for purposes of functionality, providing the ability to retain soils and slow the flow of water during peak runoff conditions. The use of trees provides additional soil retainage capacity, as well as accenting the bioswale plantings. There are many resources available to provide a plantings list – check out: www.lowimpactdevelopment.org/raingarden_design/download.htm.
All About Plants
Xeriscaping
In addition to utilizing landscaping features to collect and treat runoff, other green landscaping considerations involve, among other things, the actual selection of plant types. Simply stated, green landscape planting criteria measures the water consumption, source, and maintenance of the plantings selected – all common sense considerations. This awareness to plant selection has only increased as many municipalities begin to levy additional water entitlement fees, particularly in commercial applications, based on irrigation water demand; these fees are on top of the entitlement requirement that all landscaping be provided with high-efficiency irrigation systems. One type of planting scheme is known as xeriscaping, the selection of plantings that significantly reduce, or all out eliminate, the need for supplemental irrigation. Xeriscaping is generally most common in areas where there is a limited supply of water, particularly in the southwest. Again, there are numerous sources available to provide a list of xeriscape plantings, including annuals, biennials, grasses, perennials, shrubs, tress and vines, etc.
Of late, there is renewed interest in (and focus on) the use of native planting as our understanding and appreciation of regional differences in climate and plantings continues to grow. The native plant species in Colorado and California differ from those in Washington. Native plantings not only reduce the need for supplemental irrigation, but also lead to reduced maintenance. Companion planting, a practice of paring plants to attract (or repel) insects and other wildlife and a common practice in organic gardening, reduces not only the use of pesticides and other chemicals, but also overall maintenance as more natural growth is encouraged. For basic information on companion planting check out http://www.attra.org/attra-pub/complant.html. Whether landscape plantings are used to control and treat surface water runoff, or selected on their own merits, both applications can contribute to a more sustainable landscaping program – one that not only reduces the need for supplemental water and leads to lower maintenance needs, but also supports a more diverse and robust ecosystem. Such applications can be seen in both commercial and residential developments, and even retrofits. As such, there is indeed much benefit to giving this scope the attention and focus it deserves during a project’s completion phase.
What other gardening techniques have you seen or used to increase sustainability? Let us know!
(Photos from http://theonlinehealthjournal.com/calgary-gardens-using-rain-garden-as-natures-water-filters/ and http://ecohomeresource.com/2009/04/xeriscapes.html)