Rita's Monthly Gardening Tips, November 3, 2015
Somewhere in front of your house or a few houses downhill along the street is a storm drain. The rainwater that comes off your roof, across your driveway, and runs over other impervious (solid) surfaces flows down into that storm drain, which flows untreated in a path that leads to the ocean. Any overflow of water from irrigation in your yard follows that path as well.
In this month’s garden tip, we will look into the idea of purposely gardening in a way that encourages a smaller quantity of cleaner water that ends up in the storm drain system.
First, why is it a problem that water goes through the storm drain? Water that runs off solid surfaces picks up pollutants such as oils and chemicals polluting the water. Excess water that runs off planted areas contains nutrient content such as nitrogen and phosphorous that causes algae growth. Algae growth uses up oxygen in the water, making it hard for aquatic animals to live. Also, water that flows away from our property rather than being absorbed into the ground leaves our water table reserve so low that the trees struggle to survive. Their roots, designed to find water deep in the water table under the ground, now are dominating the surface, creating unstable growth and a challenging environment for other plants to grow. These are just a couple of the many reasons decreasing runoff is important.
Now, what can we do to help? One option is to grow a rain garden. The purpose of a rain garden is to grow plants in a place between your greatest source of water runoff and your nearest storm drain. A carefully designed rain garden will capture excess water, slow the flow, and filter impurities before it hits the storm drain system. Depending on the size of solid surfaces on your property to garden space, it is even possible to eliminate water runoff completely.
All in one fell swoop, you can have a garden that purifies runoff water, increases your water table reservoir, protects the environment, and provides habitat to birds and beneficial insects.
Below is a list of resources to learn more about how to design a rain garden and California native plants that would do well in such a garden.
http://landdesignpublishing.com/docs/LPCG%20Sections%201-3.pdf pg. 97 for a list of California native plants suitable for a bioswale, which is similar to a rain garden.