Landscape Design
One of the most reliable ways of eliminating variability in effectiveness of
outdoor conservation options is to modify the design of gardens and
landscapes. We do not base our estimates of statewide potential on this
approach, because of our fundamental assumption that there be no
change in the “service” provided by water, even though we believe that
xeriscaping and reduction in turf area produces perfectly acceptable, and
sometimes even improved, garden aesthetics. Nevertheless, the potential
for significant reductions in outdoor water use is high, and we discuss
that potential here as an option available to all homeowners.
There are two aspects to landscape design: the choice of plants and the
physical layout of the landscaped area. Water needs of different plant
species vary considerably, and some vegetation is better equipped to withstand
the hot, dry regions and periods of parts of California than others.
Water requirements for vegetation commonly found throughout the state
range from up to 1.0 ETo for cool season grasses (Kentucky bluegrass,
rye, tall fescue, red fescue, etc.), 0.7 ETo for warm season grasses
(Bermuda, Zoysia, etc.)6
, 0.5 ETo or less for groundcovers, to 0.2 ETo for
shrubs and trees (http://www.owue.water.ca.gov/docs/wucols00.pdf)
(CDWR 2000). Proper landscape layout involves controlling the area and
perimeter of turf, minimizing narrow paths or steep areas that cannot be
irrigated efficiently, and grouping plants with similar irrigation needs.
A limited number of studies have quantified savings from xeriscape practices,
typically defined as water-efficient landscaping (Table 3-7). The
North Marin Water District conducted a series of such studies and found
that proper choice of plants and careful landscape design could reduce
water use by up to 54 percent (Nelson 1994).
Less water use was not the only benefit – the water demands of the
xeriscape landscapes were more level throughout the growing season and
lacked the dramatic peak demands common to traditional landscapes.
The Southern Nevada Water District compared the water use of traditional
landscapes with those that had been converted to xeriscape. They
found that relatively few properties in each group used vastly more water
on a per-unit area basis than the bulk of the rest of the sample. Mean
monthly household consumption dropped an average of 33 percent following
conversion. The xeriscaped landscapes consumed, on average, 20
to 25 percent as much water as the traditional landscapes. These savings
took place in the year following conversion and remained stable during
the following three years of analysis.