Project Rationale and Goal
It is well understood that plants vary in their irrigation water needs (Fig. 1). Some species require very little or no water during the summer months, while others need relatively large amounts. Unfortunately, there is no authoritative resource that identifies the specific water needs of landscape plants. Certainly, field research has been conducted that identifies the water needs of some species, but this amounts to a very small percentage (less than 1%) of the species available in California wholesale nurseries. Furthermore, due to the resource challenges involved in conducting this research, it is unlikely that another 1 or 2% of species will be evaluated in the near future.
Considering the paucity of research-based information, it was reasoned that compiling information based on the collective experience and knowledge of leading horticulturists in California was far better than providing little or no guidance. This project was based largely on that rationale. Essentially, our goal was to provide users with the most comprehensive and up-to-date information available from the best sources in California. In considering the extent of the list and the extensive experience and knowledge of the regional committees involved, we believe this goal has been achieved.
Use of the WUCOLS List
Originally, the intent of the WUCOLS project was to provide guidance to landscape professionals regarding the water needs of landscape species. This continues to be the intent. Specifically, it can be used to
- assist landscape architects, designers, and planners in selecting plants for water-efficient landscapes.
- assist landscape managers in evaluating water needs of existing plantings and in creating irrigation schedules that match species needs.
- assist landscape managers who seek to modify the species composition of existing landscapes to reduce variation in water needs and create effective hydrozones.
- provide support information for formulae used to estimate water needs for new or existing landscapes.
Note: Water agencies and local authorities may opt to use WUCOLS evaluations to help meet conservation goals. When doing so, however, agencies and users must be familiar with how the evaluations were made and the specific limitations on their use. This information is provided in the following sections that describe the evaluation process, define the categories of water needs, and identify symbols used in the list.