Saving rainfall for your garden
(This post was originally written about winter rains, but is now even more applicable for desert gardens in the summer of 2023.)
Rain has finally arrived in the American Southwest. After an almost rainless summer which made our serious drought even worse, storms are now arriving one after another from both north and south Pacific. So now is the time to capture that rain water.
Use one or more of the following methods to keep water in your garden by encouraging it to stay on your property for future use or percolate down into the soil now rather than run off into the street.
Build basins
The simplest way to capture rainfall for the plants 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 and not very deep. Creating a basin all the way out to the tree canopy’s edge is ideal. An inch or two depth will create a basin to hold a good amount of water while it sinks into the earth.
Be careful not to damage the root crown at the base of the trunk. In fact, the basin shouldn’t start right at the trunk of the tree. You want to water to go to the smaller roots further out.
While most flower beds are mounded — 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. Again, be careful not to damage the roots of your plants.
If you plant in raised boxes, I hope you have good drainage on the bottom or during a heavy downpour your planter may flood and drown the plants.
Infiltration–high priced or on the cheap
Infiltration, in its 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 but 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”. Consult a landscape architect or soils engineer if you plan to do this.
In the less expensive version of infiltration, 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. Some people recommend using French drains, the drain pipes with holes, set vertically into the soil so they are mini-wells.
In the super-cheap version, 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.
Add a cistern or rain barrel… or seven
Our last suggestion is to add a cistern or rain barrel to capture rainfall which you can use later by pumping the water out for irrigation. Unlike infiltration which is designed to allow water to spread out underground during a rain storm, a cistern is supposed to hold water in the container, not diffuse it.
If you want to add an underground cistern–which is essentially a well filled with rainwater–you should consult with a landscape architect or soils engineer because there are certain critical engineering issues involved. The sides and bottom must be sealed to prevent water from escaping and the system must have an overflow drain. If water overflows in the wrong direction you may have serious and potentially expensive erosion problems.
On the other hand buying a big plastic barrel or one of the large above ground cisterns–prices start at about $100 and go up depending upon the size–can be a quick and easy method to store the rainfall from the downspouts on your roof until you use it later.
Are cisterns illegal?
In Colorado and Utah having a cistern on one’s own property to collect water used to be illegal. But no longer. Now Coloradans can have 2 rain barrels with a total capacity of 110 gallons of water for use on their own property. In Utah homeowners can save up to 2500 gallons in above or below ground cisterns to store water for use on the same property. In both these states, please check for specific local regulations.
Many other states, including Nevada and California, have regulations or are planning to enact them, about water harvesting and usage. California, for example, is encouraging water harvesting. To see if your state has regulations, go here.
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