The mixed blessing of the U.S. Southwest monsoon for gardens

Monsoon rainfall season has arrived in the Arizona, Nevada, California — all over the U.S. Southwest.  The infrequent, but intense, summer rains sweeping up from the Gulf of Mexico are, however, nothing like the drenching daily downpour of the South Asia monsoon that trapped that young soccer team in a flooded cave in Thailand. The danger here is of hikers being caught in a flash flood in a canyon or cars being swept away on a road.

On the other hand our summer rainfall cloudbursts can add life to your garden if you take steps to retain part of the water falling on your property.  (Except in Colorado. More about this below.)

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 at least 3 feet from the tree trunk and not too deep. Be careful not to damage the root crown at the base of the trunk or the roots of the tree.

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 rainfall as possible. The organic material in your flower beds will also retain more water than ordinary desert soil.

3.  Another technique is to dig or drill narrow, deep holes–1 or 2 feet in depth–spaced apart in a circle around trees and shrubs just below the ends of the branches. These holes will fill with rain which will then seep into the soil. You may want to consider dropping coarse gravel or small rocks into the holes to keep them from collapsing. These holes are also good for deep watering trees and shrubs to encourage growth of deeper, stronger roots. And deeper roots mean more stability when winds howl across the landscape in Spring and Fall.

Now for the technique that is more expensive–it’s called infiltration–and it is a problem in Colorado. That State by law owns all the water rights within its borders and individual citizens cannot retain water on their property without permission from the State because it would be denying that water to another person downstream who may have already obtained water rights from the state.  And they actually prosecute people for this! IMPORTANT: THIS LAW IN COLORADO HAS BEEN CHANGED AND IT’S NOW OK FOR HOMEOWNERS TO HARVEST RAINFALL FOR USE ON THEIR OWN PROPERTY.

California has passed a law to encourage homeowners to build cisterns on their own property.

Okay…back to saving summer rainfall.

4. Infiltration involves digging a sizeable pit on your property which will receive water from rain runoff from your roof.  This means installing rain gutters and downspouts, which are uncommon on desert homes. 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”. If you decide to go this route, be sure to get a licensed soils engineer to draw up plans to avoid a disastrous collapse.

5. Now for the last suggestion: channel the roof rainfall through downspouts into 50 gallon (or larger) plastic containers. This is a modern variation on the old time cistern, a sealed and lined pit to hold water for later use. You can use the water for irrigation later. 

And in between summer monsoon downpours remember to water your plants in pots. They are like animals in a zoo: you have to feed them every so often and water them daily.