September 29, 2018
After a few years of near-average rainfall, warnings about drought can seem less urgent. Yet the winter rains on which we depend are far from predictable, with annual rainfall (measured at Lake Lagunitas) ranging from 18 to 112 inches. It takes only two years of rainfall below the average annual 52 inches to seriously deplete our reservoir water supply. In addition to seasonal droughts, groundwater pollution and population growth contribute to water stress. Typically, around 50 percent of residential water goes into our landscapes during summer months, so good gardening practices mandate that we use our water efficiently.
Most Marin landscape plants, including some natives, require additional water during the dry summers. Our challenge is to avoid waste while providing our plants the right amount of needed water. State and district water conservation regulations enacted in 2015 prohibit irrigating between 9 a.m. and 7 p.m., irrigating more than three days per week and irrigating during and 48 hours following a rainfall. Other restrictions include using a hose without a shut-off nozzle, allowing irrigation overspray or runoff, hosing down sidewalks and driveways, and using non-recirculating decorative fountains.
In contrast to the previous regulations that targeted waste, long-term water use efficiency legislation, recently enacted in 2018, requires development of objectives and standards for indoor and outdoor residential water use. While indoor residential standards are established on per capita use, outdoor standards are to be based upon a community’s climate and the amount of landscaped area. This is where the Model Water Efficient Landscape Ordinance (MWELO) becomes important. The ordinance establishes reporting requirements for local water districts and sets landscape guidelines to optimize water use. The new efficiency goals will address the challenge of matching water supply to plant requirements as determined by the Water Use Classification of Landscape Species (WUCOLS IV). WUCOLS categorizes plants according to type, climate region and level of water need. Using the WUCOLS categories, the estimated total water use and the maximum applied water allowance will guide landscape plant selections. Installation of high-water use plants, such as lawn turf, will be restricted.
While it is helpful to know about the current and pending regulations, wise watering is really a matter of observation and common sense. The goal is to replace the water lost through the plant leaves (transpiration) and from surface (evaporation) in your particular microclimate. This combination is referred to as evapotranspiration. The rate of evapotranspiration changes with day length and weather conditions. Irrigation controllers allow you to manage the amount of water delivered to landscape plants and to make seasonal adjustments. It’s important to make certain your irrigation systems are functioning efficiently with no broken lines, plugged emitters or spontaneous geysers. Of course, it is always preferable to organize your system according to hydrozones in which plants with similar water needs are supplied by the same valve. When this isn’t possible, give some attention to the amount of water delivered by the emitters in order to direct appropriate amounts to each plant. Hand watering, although less efficient than automatic drip, can be an alternative in some situations and a hose meter can be used to measure the amount of water applied.
Fortunately, here in Marin, there are many resources to assist us in watering wisely. Both the Marin Municipal Water District (MMWD) and the Northern Marin Water District (NMWD) provide a wealth of conservation information on their websites and offer additional consultation services to residents on request. MMWD publishes a weekly watering schedule as a guide to replenishing the moisture lost through evapotranspiration. NMWD offers a water smart home survey that includes a landscape irrigation system efficiency test. You can also schedule a free Marin-friendly garden walk with a UC Marin master gardener and receive information and advice on improving irrigation practices in your own garden. Go to ucanr.edu and click on the main page link to “Garden Walks” for scheduling your free evaluation or call the help desk.
Don’t wait for drought warnings to prompt your wise watering. If we all do our part, we can sustain our beautiful gardens and conserve our precious water resources.