Water Use Classification of Landscape Species (WUCOLS)

WUCOLS Update: January 2024

Under the guidance of the California Center of Urban Horticulture, the review and update of WUCOLS IV to create version V employing the evaluation process outlined in the WUCOLS III update (WUCOLS, see P7 “The Evaluation Process) has commenced.  The qualitative research approach will be employed for updating the database. 

Scope of Work

Volunteers from horticultural industry, academia, government agencies and NGO’s will meet to review and provide plant water use recommendations for up to 1,700 new entries (taxa). Representatives will be from 6 different CA climate zones and will ensure that the same plant growing in multiple CA regions will be assigned a water use factor that accounts for climatic differences.  Online technology, such as ZOOM or Microsoft Teams, will be utilized for the meeting venue, and meeting facilitation will be conducted by PI or Program Manager for reviewing proposed taxa and assigning water use ratings/PF’s.  Upon completion of the review process for all new taxa, data will be reviewed (accuracy) and formatted for uploading to the existing database administered by the CA Center for Urban Horticulture, UC Davis.  Prior to uploading data, a cursory review of existing database will be conducted to ensure database capability.  Database will undergo review and beta testing prior to going live online.  Google Analytics will be employed periodically for measuring user impact. 

Work Completed Year-to-Date

1.  Wholesale nursery growers submitted very low and low water use taxa (plants) for review.

2.  Plants from nursery growers crossed referenced against WUCOLS IV list.

3.  Excel file template created for reviewing taxa not found in WUCOLS for regional review.

Next Steps

1.  Identify and and request horticultural professional volunteers to review.

2.  Volunteer qualifications:

  • Twenty+ years of experience in the landscape industry
  • Knowledgeable about native and non-native plants
  • Experience with a large number of species in the respective region
  • Experience with plant performance in urban residential, commercial, and non-residential landscapes
  • Experience with landscape irrigation systems (subsurface and surface)
  • Working knowledge of MWELO and WUCOLS data base, including an understanding of the User Manual
  • Effective collaborator in an online platform for Committee meetings
  • Ability to be objective and respectful of others’ opinions

Please contact Cheryl Buckwalter landscapeliaisons@gmail.com or (916) 207-8787, or Dave Fujino at dwfujino@ucdavis.edu with questions and/or to express your interest to participate on a Regional Committee by February 1. We also welcome your recommendations for other qualified professionals to participate and ask that you please provide contact information.

3.  WUCOLS Review Process

  • Independent, self-paced review the list of approximately 1,200 new plants proposed to be added to WUCOLS and assign a water-use classification for each.
  • Independent, self-paced focused review of the current WUCOLS IV list of 3,546 plants to identify plants that are no longer commercially available, determine if plants previously unfamiliar to the committee that could not be rated, can now be given a rating or, if a plant was determined to be inappropriate for a region can that rating be revised.
  • March 15 or earlier - The due date for items 1 and 2 above to be completed and the lists with your ratings returned to me.
  • Everyone’s ratings will be compiled by CCUH.
  • Mid-April, plants in which there was not consensus will be evaluated by the regional committees via Zoom meeting(s).
  • Mid-May - The target date for regional committees to have their review complete.

WUCOLS Press Release: September 2023

Attention all horticultural professionals and garden enthusiasts! The Department of Water Resources (DWR) has partnered with the UC Davis California Center for Urban Horticulture to update a free, online database that helps users find plants suitable for their region. With approximately 50 percent of urban water use going towards outdoor landscapes, this database will help residents adopt climate-ready landscapes that promote smart water use and help our natural pollinators thrive.   

The Water Use Classification of Landscape Species database offers water use data for more than 3,500 plants and helps users find the perfect plants for their water needs. Using the Water Use Classification of Landscape Species database, users can search for plants by region, water requirement, and plant type. Thanks to funding from DWR, the database will receive updates later this fall when it is the perfect time to plant and   will improve the user experience as California continues to embrace water conservation as a way of life.

“We’re   excited to support an update to a great resource offered by UC Davis and the California Center for Urban Horticulture,” said Ryan Bailey, DWR Water Use Efficiency branch manager. “This update means the general public and our industry professionals will have the necessary information to make water-wise decisions that improve water conservation while planting a beautiful landscape.”

With California’s new climate reality involving frequent swings between extreme drought, flooding, and everything in between, smart water use – indoors and outdoors – continues to be important rain or shine. The Water Use Classification of Landscape Species database can help Californians make more informed decisions about their landscape and the types of plants they select based on local conditions.

“It has been almost 10 years since the last review and update to the Water Use Classification of Landscape Species database, database, and we are eager to begin the process of adding another 1,700 plant groups.” Said Dr. David Fujino, executive director for the California Center for Urban Horticulture. “We appreciate the support of the Department of Water Resources and the participation of the horticultural industry to provide this timely update.”

In addition to new plant entries, the updated database will include improved search functions allowing users to interact with maps to identify areas of interest, find results faster, create a “favorite” plant list, and download hi-resolution photos of low water use plants. The updated database is expected to launch in November 2024. Until then, users can use the existing Water Use Classification of Landscape Species database, information at https://ccuh.ucdavis.edu/wucols.

For more information on water use efficiency updates, visit DWR’s Water Use Efficiency webpage. For water conservation tips, visit saveourwater.com.

About WUCOLS: 

Water conservation is an essential consideration in the design and management of California landscapes. Effective strategies that increase water use efficiency must be identified and implemented. One key strategy when landscaping is to group plants with similar water requirements.  By supplying only the amount of water needed to maintain landscape health and appearance, unnecessary applications that exceed plant needs can be avoided. Doing so, however, requires some knowledge of plant water needs.  The WUCOLS searchable database allows you to create your “favorite” plant list by water needs (very low, low, moderate and high) for your climatic region.

WUCOLS IV provides evaluations of the irrigation water needs for over 3,500 taxa (taxonomic plant groups) used in California landscapes. It is based on the observations and extensive field experience of thirty-six landscape horticulturists (see the section "Regional Committees") and provides guidance in the selection and care of landscape plants relative to their water needs.

Home Page Photo
WUCOLS IV provides an assessment of irrigation water needs for over 3,500 taxa. Photo by Ellen Zagory.

About WUCOLS IV (The 4th Edition 2014)

The 4th edition (Costello, L.R. and K.S. Jones. 2014. WUCOLS IV: Water Use Classification of Landscape Species. California Center for Urban Horticulture, University of California, Davis.  http://ucanr.edu/sites/WUCOLS/) represents a substantial expansion in the number of plant evaluations. Over 1,500 entries have been added to the 3rd edition list, for a total of 3,546 entries. Essentially, the great majority of taxa available from wholesale nurseries in California are included.

Unlike the 3rd edition, the 4th edition includes evaluations of many cultivars and hybrids. For a number of species (e.g., Ceanothus spp.), water needs of cultivars were thought to be sufficiently different than water needs of the species and were evaluated separately. In addition, a number of cultivars do not have a specific epithet, such as Erysimum ‘Bowles Mauve’, and the species from which it is selected is not obvious. Hence, only the cultivar could be listed.

In addition, a number of species evaluations made in previous editions were revisited by the regional committees. If the committees believed that the evaluation of plant water needs should be changed (raised or lowered), it was changed. In some cases, a “?” was replaced by VL, L, M, or H (see the section “Categories of Water Needs”). As a result, users should be aware that species assignments from WUCOLS I, II, or III may not be the same as those found in WUCOLS IV.



If you are using the WUCOLS list for the first time, it is essential that you read the User Manual. The manual contains very important information regarding the evaluation process, categories of water needs, plant types, and climatic regions. It is necessary to know this information to use WUCOLS evaluations and the plant search tool appropriately. To access the User Manual, click on the tab and view specific topics.