WUCOLS Update: April 2025

Under the guidance of the California Center of Urban Horticulture, the review and update of WUCOLS IV to create version V employing the qualitative research evaluation process outlined in the WUCOLS III update (WUCOLS, see P7 “The Evaluation Process) is nearing completion date June 2025.  

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 1,200 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/Plant Factors (PF).  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.  

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 approximately 1,200 taxa (WUCOLS V) not found in WUCOLS IV.
4. Volunteers for all 6 WUCOLS regions identified (see Regional Committee List below).
5. Individual reviews of WUCOLS V plant list completed by all 6 Regional Committee members.
6. Individual reviews consolidated by region and plant list created for those plants where committee consensus was not achieved (gap list) along with committee reviewer’s comments.
7. Regional committee meetings conducted to gap lists for achieving consensus on plant water use ratings and comments.
8. Upload of plant water use ratings complete along with comments into WUCOLS database. 
9.  Addition of “new” WUCOLS plant factors and edits are “live” as of March 25, 2025.

Next Steps

1.  Complete edits to the existing WUCOLS IV plants.

• Update water use ratings, if applicable
• Nomenclature
• Remove plants deemed not commercially available
• Note potential invasive species, if applicable

2.  Complete WUCOLS V manual.

3.  Update and publish WUCOLS V webpage and Table of Contents

For specific questions regarding update status and questions on content, please contact Dave Fujino at dwfujino@ucdavis.

WUCOLS V Acknowledgements

The following tables list the horticultural professionals who spent countless hours individually and, in their committees, reviewing and providing water use ratings (Plant Factors) of approximately 1,200 new taxa and to be added to the current WUCOLS IV online database.  Please join me and the WUCOLS management team (Cheryl Buckwalter, Landscape Liaisons, Don Franklin, Hunter Industries (retired), and Emily Finch, CCUH Program Manager) in thanking the WUCOLS regional committee members.  With their commitment, WUCOLS V is now updated and enhanced. 

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.

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.