Guide to Estimating Irrigation Water Needs of Landscape Plantings

Other Important
Information About
the Guide
Variation in Regional Evaluations
Variation in species evaluations among regions occurs
in many cases. Two patterns of variation are
found:
1. where the variation ranges from less water
needed in cooler climates to more in warmer
ones, and
2. where less water is required in warmer climates
than in cooler ones.
The following examples are typical cases:
Case 1— Laurus nobilis, sweet bay
1 2 3 4 5 6
L L L L M M
This is the most common variation. It merely indicates
that certain species were thought to require
more water in warmer climates.
Case 2—Gleditsia tricanthos, honey locust
1 2 3 4 5 6
L L M L L L
A warmer region indicates a lower water requirement
than a cooler region. This case reflects differ-
ences in observation and experience among regional
committees.
Zauchneria spp., California fuchsia
1 2 3 4 5 6
L L VL L / M
This example shows both cases. Sometimes, for
certain California natives and other drought tolerant
species, there was agreement that the plant would
grow with little or no irrigation, but opinions varied
as to how well it would perform in a managed landscape
under those conditions.
Drought Stress/Insect Attack Relationships
Although some species perform well with little or
no irrigation water, their susceptibility to insect attack
and injury may increase with water stress. For
example, many Eucalyptus species perform well in
non-irrigated conditions in many parts of California.
When drought stressed, however, they become
susceptible to attack and injury from the Eucalyptus
long-horned borer. This is the case as well for
Monterey pine (California five-spined engraver
beetle) and white alder (Flatheaded borer). For these
species, evaluations were made with consideration
given to water stress and pest interactions. For example,
although Eucalyptus globulus will perform
well in Regions 3 and 4 with little summer water, it
was assigned to the “moderate” category to minimize
its susceptibility to borer injury.
Shade
Most species were evaluated for full sun conditions.
Light intensity and duration varies with seasons,
microclimates and proximity to the coast. Many
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