What is a WUCOLS?

What is a WUCOLS?

WUCOLS is a publication that provides water usage guidance to landscape architects and other landscape professionals.

WUCOLS stands for the Water Use Classification of Landscape Species.

A group of smart university professors, researchers, and landscape professionals determined how much water landscape species require to maintain an aesthetic appearance.

The Results Were Shocking!

Most common landscape plants were overwatered—extremely overwatered. In fact, a lot of irrigation could be reduced and the plants stayed healthy and looked fine, too.

Forty-one of the state’s most experienced landscape and horticulture experts conducted field observations on over 1,900 landscape plant species and evaluated each species water needs.

The WUCOLS research team assigned each plant a water use category based on their water use in the landscape.

  • High
  • Medium
  • Low
  • Very Low

In addition to classifying plants based on the water they needed, each water use category received a numerical coefficient.

  • High = 70-90% of reference evapotranspiration
  • Medium = 49-60% of reference evapotranspiration
  • Low = 10-30% of reference evapotranspiration
  • Very Low = <10% of reference evapotranspiration

The plant factor can be used with Landscape Coefficient Method to estimate water use of plants and develop irrigation schedules that would adequately water the plants. By only irrigating with the amount of water the plants need, the states precious water resources can be conserved.

Not only were plants assigned a water use factor, the crack research team determined the water needs for plants in different parts of the state. Researchers determined the extent of each region based on the area’s evapotranspiration rate. A particular plant’s water needs are based on the evapotranspiration rate. Therefore, the plants should perform roughly the same in areas with the same reference ETo.

WUCOLS Regions

These are the 6 regions used in the WUCOLS manual:

  1. Region 1—North-Central Coastal
  2. Region 2—Central Valley
  3. Region 3—South Coastal
  4. Region 4—South Inland Valley
  5. Region 5—Intermediate and High Desert
  6. Region 6—Low Desert

The WUCOLS manual shows the water use needs of each plant in the six different regions.

Some plants are remarkably consistent and are the same water use category in all zones. For example, passionflower (Passiflora spp.) is in the medium water use category in all zones. Other plants have different water needs depending on their location. Coast live oak (Quercus agrifolia) has is classified as very low water use in Zones 1 and 2. However in Zones 3 and 4, the same plant is only categorized as low water use. In the low desert, coast live oak’s water needs are moderate in the low desert. A plant’s water requirements can change depending on where a plant is grown.

How to Use The WUCOLS Manual

Landscape architects can use the Information in the WUCOLS manuals in a few ways.

  1. Create Plant Palettes
  2. Estimate Water Use
  3. Develop Irrigation Schedules

Create Plant Palettes

Landscape architects can select plant species for a project based on their water needs. Group plants with similar water needs in the same hydrozone.

Estimate Water Use

Since the WUCOLS manual provides plant water use factors, landscape architects can use this information to estimate how much water a landscape may use in a given year. The California Model Water Efficient Landscape Ordinance requires landscape architects to estimate the annual applied water usage.

Develop Irrigation Schedules

Since the WUCOLS manual identifies the percentage of the reference ETo the landscape plants need to perform adequately in the landscape, landscape architects can use this information to develop weekly or monthly irrigation schedules for the irrigation controller. An accurate schedule ensures that the plants get the water they need and saves water by reducing excessive irrigation.

WUCOLS is a treasure trove of plant water use information for California landscape architects.

For More Information

The California Department of Water Resources funded the project which was conducted by the University of California Cooperative Extension.

You can download the WUCOLS manual here.


John is a landscape architect who is currently preparing to take the California Supplemental Exam to become licensed in California. He is currently a licensed professional landscape architect in Georgia and Florida. John graduated from California State University, Pomona with a BSLA degree in landscape architecture in 1997 and has extensive practice experience in residential and commercial landscape design.

Posted in Regulatory Agencies, State Agencies, Water

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