In the Garden:
Southwestern Deserts
August, 2008
Regional Report

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This urban driveway's parallel concrete tracks have a permeable center planted with low-growing flowers.

Permeable Hardscaping

There are many ways to harvest rainwater in the landscape, including directing water to planting areas using swales and dry streambeds or collecting and storing rain in cisterns and barrels. A simpler way to take advantage of rainwater is to allow soil surfaces to remain permeable wherever possible.

Permeable surfaces let rainwater penetrate the soil and remain on your property. It's been the norm for many years to build sidewalks, driveways, and patios from impenetrable substances, such as concrete slabs or flagstone, brick, or pavers set into mortar. These hard surfaces are usually sloped to force rain to run off individual properties into storm drains or community retention basins. If, instead, that rainwater is encouraged to soak into your landscape, the moist soil acts as a "water bank," allowing plant roots to tap the water as needed. It is easier and cheaper to store water in the soil than in cisterns or barrels, and you don't have to worry about freshness, mosquito larvae, or getting the water out to use it!

Fast-Draining Surfaces
Permeable surfaces include organic mulch (bark chips, chipped matter) and decomposed granite mulch. Another option is to set flagstone, brick, pavers, chunks of recycled concrete or similar materials into sand, without mortaring the joints. You still have the benefit of a firm surface for walking or seating arrangements, but rain can soak into the cracks. This works for patios set with detailed brick or paver patterns, or a more casual look such as flagstone slabs or chunks of recycled concrete spaced as stepping stones for pathways.

Advantages to Permeable Materials
Rain contains nutrients and is less salty than water from most municipal water sources. Salt buildup in the soil leads to salt burn, which shows up initially as yellowing and browning along the edges of leaves. If left uncorrected, too much salt in the root zone can kill a plant. Use permeable surfaces to keep rainwater on your property to give your plants a healthy drink.

Another advantage is that permeable surfaces trap and retain less heat than traditional hardscape surfaces. Thus they help to reduce the urban heat island effect, while cooling our outdoor living spaces. If you live without HOA restrictions, consider a permeable driveway, or a partially permeable driveway using parallel concrete tracks with a center planted in low-growing flowers like sweet alyssum and verbena. Not only will it lighten the heat buildup around your home, it will be pretty, too!


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