The grass is always greener

The Grass Is Always Greener

By Craig A. Wilson, Water Management Director Once upon a time not so long ago, a community grew up in the desert where surprisingly, water was available for all their landscaping needs. Trees were planted and grass grew all year round. Over the course of time a new reality emerged. Then came Mark Watney (from The Martian by Andy Weir) to show us the way by “doing the math.”

The math is really straightforward. Landscape needs a certain amount of water to thrive and do what it is designed to do; add value to your property with aesthetic curb appeal, create a pleasant and relaxing environment, provide a playground for you and your family and control the dust. Yep, that last part can be as important as the first. Crushed granite seems to be the favorite where grass is banished.

Back to the math. Landscape demands a balance between the water it needs and the water it receives. Plants need water to live and the amount needed can be quantified; the information is readily available. The easiest way to think about it is to imagine a pool of water. We know how much water will evaporate from a pool, about 70 inches of water a year per square foot of pool area; more in hot years, less in cooler years. Grass will go through a lot of water using up about as much as a pool of water, about 85% as much water or 60 inches per square foot in a year. From where does that water come? Not rain; remember we live in a desert where by definition we receive less than 7 inches of rain a year. If one could collect all the rain that fell on one’s property, it would only be enough water to irrigate about 12% of a typical yard. Kind of the same problem Mark Watney faced; living with scarce resources until rescue comes.

We can cheat, however, and take water from the hose to make up for what nature does not provide. In the end though, the math still counts. There is still that 53 inches of water left to be found to sustain the grass, that is, for every square foot of grass, over the course of a year that grass will take a column of water over four feet high to stay healthy. Each adult, at 1.5 gallons per day needs about 75 cubic feet of water per year, i.e., a column of water on a one square foot base 75 feet high. Another way of looking at it - a 3 foot by 4 foot plot of grass needs the same amount of water that an adult needs each year. Granite can get by on 7 inches a year. Remember, water makes living in the desert possible - make the best of it.