Plan to Plant

Rain Gardens

Rain gardens are a simple link that can be established as part of an overall approach to managing storm water runoff through a particular site. The importance of rain gardens in any landscape is their ability to recharge subsoil moisture, by reducing water runoff whilst promoting storm water infiltration.

Rain gardens function as water absorption and retention areas. The smallest of depressions have the ability to capture storm water, sediments and even pollution thus improving water quality in post storm events in all nearby waterways. The second important reason is that habitat is created for plants and wildlife. Ponds can be temporary (ephemeral) or more permanent in the landscape. Water is an important aspect in the environment.

Not all sites are suitable for rain gardens. The predominating factor that excludes some sites is simply the soils capacity for natural drainage. To test if your site is suitable for a rain gardens we check the water infiltration rate in your soil. Dig a hole about 20 cm deep and fill this with water. If after 24 hrs this water remains in the hole it has poor drainage. This type of site is unsuitable for rain gardens as it creates poor soil conditions for plants as well as soil organisms.

The rain garden in your landscape

Rain gardens can be simple or complex in construction. In a built environment, they can be a very ornamental feature. In a natural environment they are often subliminal in appearance as simple as a depression or swale. The common theme to all is the concave depression that is technically referred to as a bioretention basin.

Bioretention basin

The general principle of bioretention basins is the collection and storage of water in a landscape. Gravitational force moves water directly to the lowest point of the site. Water collects and accumulates in these low areas where it either infiltrates into the soil, or it is evaporated back to the atmosphere. In many circumstances the site is often well planted and the water is used by many plants resulting in its transpiration back to the atmosphere. Most of the water will be used on site, yet in a storm event some overflows will occur. The idea of capturing a fair share and then allowing excess to return back to nature is an important consideration in permaculture.

Natural wetlands

Another important aspect of bioretention basins are their ability to act as either man-made or natural wetlands. Wetlands are recognised as filtering mechanisms for sediment and pollution. The plants found growing in wetlands simply filter out sediment particles and contaminants from the water and then assimilate these materials back into their own root and foliage system. Much of what is understood about wetlands is that they are an important buffer area for the absorption and decomposition of organic matter and pollutants to the surrounding environment. They are indeed an important part of the overall health of our environment.


In landscapes, rain gardens are more commonly seen in larger developments and in rural /acreage sites. Many residential homes are willing to capture storm water from the roof trough down water pipes or to a simple water tank. We should consider that many extra opportunities exist in an urban situation, and by investigating the storm water chain of events closely we can perhaps channel more of our efforts into small bioretention basins and other water conservation methods rather than continuing to allow storm water to flow out to a street gutter.

>> For more information about rain gardens contact me to discuss the suitablility for your property

Site Assets

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