How Gardens Newsletter: Techniques for saving rainfall for use in your garden

Hot Gardens Newsletter: Summer 2008

Saving rainfall for your garden

Hot Water Season. “Monsoon” season has arrived in the American Southwest. While the hard summer rains are nothing like the drenching daily downpour of the South Asia monsoon, our cloudbursts can add life to your garden if you take steps to capture some of the water that falls on your property.

1. The simplest method to capture rain in your garden is to dig shallow circular trenches or basins around your trees and shrubs. The basin edge should be 3 feet or more from the tree trunk. Be careful not to damage the root crown at the base of the trunk. You may already have shallow basins in place for regular irrigation — consider digging them a bit deeper to keep more rainfall there. (And be sure to turn off your irrigation system on monsoon days!)

2. While most flower beds are raised — hopefully because you add a thick layer of organic mulch twice a year — you may want to consider digging small basins in the center of the beds to capture as much rain as possible.

Harvesting rain in larger amounts

3. Another technique, a variation on infiltration, is to dig or drill narrow, deep holes spaced apart in a circle around trees and shrubs. These holes will fill with rain which will then seep into the soil. To do this effectively, you may have to line the holes with strong but permeable material to help prevent the sides from collapsing into the holes while allowing water to escape into the root zone. Really coarse gravel or small rocks may also keep the holes from collapsing. Deep watering like this will encourage trees and shrubs to grow deeper, stronger roots. And deeper roots mean more stability when winds howl across the landscape in Spring and Fall.

4. Infiltration, in its better known and more expensive form, involves digging a sizeable pit on your property which will receive water from rain runoff from your roof. This means rain gutters and downspouts must be installed. The pit must be lined with a strong, permeable material and have an overflow to channel excess water safely away from your home. Water will seep from the pit into the surrounding soil, thus “irrigating from underground”.

5. Our last suggestion: add a cistern to capture rainfall which you can then use by pumping the water out for irrigation. A cistern is essentially a shallow well or pit that fills with rainwater, rather than groundwater. The sides and bottom are sealed to prevent water from escaping and the system must have an overflow drain. For a cistern or an infiltration pit we strongly recommend that you consult with a landscape architect. If water overflows in the wrong direction you may have serious and potentially expensive erosion problems.

Death by Drip Irrigation

For decades drip irrigation has been recommended as a good way to water plants with little or no wasted water. But it turns out they may be dangerous for your plants’ health! At a recent presentation at the Mediterranean Garden Society, there were experts who advised against using those tiny drip emitters because basically they do not provide sufficient water for plants to survive. Larger emitters — one inch in diameter — may do the job correctly. And now there are new water-efficient sprinklers, too and rain-sensing irrigation systems that save water and your plants, too.