July 18, 2014
By understanding plant water needs, you can reduce waste.
The prolonged drought in California coupled with rapid population growth and climate change has put new emphasis on the use of water in the landscape. Most residential water use, roughly 60 percent, is typically used outdoors. Of that, 20 percent is wasted by inefficiency. These put residential landscape water use in the crosshairs of those tasked with water conservation. Understanding plant water needs, prioritizing its use and applying it responsibly can be complex.
Potable, or drinkable, water is one of our most precious resources. Rainwater, abundant in the winter but relatively expensive to store, is next. Reclaimed water that comes from sinks, showers and laundry, is available in quantity year-round, but necessitates a system to capture it. It is illegal to store residential gray water; it must be used as it is generated. Reclaimed water is rarely seen in residential landscapes, but that may be changing as potable water becomes more scarce — and expensive.
There should be more consideration placed on investing in rainwater storage and gray-water systems. Gray water should be used first and daily as it is generated, then stored rainwater with potable water, if necessary, used last. The question then comes down to which plants should be watered first and how much.
Generally, put highest priority on heritage trees and desirable trees prone to drought-stress-based diseases. Food crops and fruit trees come next. Shade trees are highly valuable when their energy savings is considered. The next level of priority would be those plants that are best suited to your climate and especially those with higher habitat value. Plants that did not evolve in a Mediterranean climate should have their appropriateness questioned. Then find out what your Marin Municipal Water District climate zone is: Northern, Central or Southern.
It should go without saying (but I'll say it) that non-recreational or purely aesthetic turf falls into inappropriate plants category. More responsible alternatives should be considered.
The next question is how much and how often. Think in terms of replacing water lost and getting it into the root zone. "Evapotranspiration" (ET) is the combination of water lost through plant leaves (transpiration) and water lost from the surface (evaporation) in your microclimate. The Water Use Classification of Landscape Species, or WUCOLS, resource allows you to see what specific plant species need in terms of the percent of your specific ETo ("reference ET") in inches. MMWD makes it simple by not only posting the daily and weekly ETo every Friday on its website, but also suggesting how many minutes to run your irrigation each week. This should be adjusted according to your soil type to avoid run-off.
Further help can be found by having a Master Gardener trained in landscape water management come to your garden. Sign up for a Marin Friendly Garden Walk by calling 473-4204. If you think adjusting your irrigation controller every week (or better, daily) is a hassle, consider taking advantage of the MMWD Smart Controller Rebate program by calling 945-1527. These controllers, once programmed correctly, will do this for you.