Water Use Classification of Landscape Species (WUCOLS IV)
Water Use Classification of Landscape Species (WUCOLS IV)
Water Use Classification of Landscape Species (WUCOLS IV)
University of California
Water Use Classification of Landscape Species (WUCOLS IV)

Categories of Water Needs

Fig. 2. Five-finger fern was assigned to the “high” water needs category in four regions.
Fig. 2. Five-finger fern was assigned to the “high” water needs category in four regions.

Category

Abbreviation

Percentage of ETo

High

H

70–90

Moderate/Medium

M

40–60

Low

L

10–30

Very Low

VL

< 10

Species were evaluated as needing high (H), moderate/medium (M), low (L), and very low (VL) amounts of irrigation water. Expressed as a percentage of reference evapotranspiration (ETo)[1], these categories were quantitatively defined as follows.

Fig. 3. Cone flower was assigned to the “moderate” water needs category in all regions.
Fig. 3. Cone flower was assigned to the “moderate” water needs category in all regions.
Water needs categories were assigned for each species in each of the six regions. The category High contains species requiring the greatest amount of water during the summer months to maintain acceptable health, appearance, and growth, such as white alder (Alnus rhombifolia) and five-finger fern (Adiantum aleuticum) (Fig. 2). Species in the category Moderate/Medium need lesser amounts of water, such as ivy geranium (Pelargonium peltatum) and cone flower (Echinacea spp.) (Fig. 3). Species in the category Low are considered to be water conserving because they perform well with relatively small amounts of irrigation water, such as carob (Ceratonia siliqua) and strawberry tree (Arbutus unedo). (Fig. 4).

Fig. 4. Strawberry tree was assigned to “low” water needs category in four regions.
Fig. 4. Strawberry tree was assigned to “low” water needs category in four regions.
Species assigned to the category Very Low were classified as needing no irrigation except during years of below average rainfall for the region, such as chamise (Adenostoma fasciculatum) and matilija poppy (Romneya coulteri) (Fig. 5).

If disagreement existed regarding a category, the higher category was assigned. For instance, if some members thought a species was in the category Low, while others thought it was in the category Moderate/Medium, it was assigned to Moderate/Medium. With this in mind, users should be aware that lesser amounts of water may be used for a species, but greater amounts generally will not be warranted.

Fig. 5. Matilija poppy was assigned to the “very low” water needs category in four regions.
Fig. 5. Matilija poppy was assigned to the “very low” water needs category in four regions.
If the committee was not familiar with the species or did not have experience growing it in the region, a “?” was assigned. This does not imply that the species should not be planted and tested in the region, however.

If the committee did not think the species was appropriate for the region, a “/” was assigned. The performance of these species was believed to be truly unsatisfactory for the region. For instance, species that grow in the North-Central Coastal region were considered to be not appropriate for the Low or High Desert regions. Additionally, species that are frost sensitive were considered to be not appropriate for the Central Valley.

In some cases, all species in certain genera were evaluated as a group (e.g., Dianthus spp.). Essentially, all species of these genera were thought to have similar water needs.

Many species on the WUCOLS list can be irrigated at levels lower than those identified by regional committees. In some cases, such a reduction in irrigation will mean survival of the plant but not necessarily good performance. For example, many California native species are adapted to summer-dry conditions and survive from year to year, but their performance and appearance may be compromised. For the WUCOLS project, species were not evaluated for survival levels of irrigation. Rather, category assignments were based on an assessment of the level of water needed to maintain satisfactory health, appearance, and growth (see the section “Standard Conditions,” below).


 [1] For further information on ETo, see the Model Water Efficient Landscape Ordinance (MWELO) at http://www.water.ca.gov/wateruseefficiency/docs/MWELO_TbContent_Law.pdf.

 

Page Last Updated: September 16, 2016
CCUH transparent
DWR logo
UCD blue2 transparent
Webmaster Email: lldodge@ucdavis.edu