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In the Beginning...

Karrie Reid and Loren Oki (JA Sisneroz)
Karrie Reid and Loren Oki (JA Sisneroz)

The UC Landscape Plant Irrigation Trials (UCLPIT) began as a graduate student research project taken on by Karrie Reid in 2004 under the guidance of her advisor Loren Oki, UCCE Specialist at UC Davis. The original scope of the trial was to evaluate plants on the UC Davis Arboretum All-Stars list. The original trial evaluated the response of 10 species of California natives to four irrigation treatments.

Although other water-use trials had been performed on landscape plants, these trials, as conceived by Dr. Oki, were the first to schedule the irrigation frequency of a fixed volume of water based on reference evapotranspiration (ETo). Previous water-use trials applied irrigation on a preset schedule, e.g. weekly, or used ETo to adjust the amount of irrigation applied. The results of this novel trial were published in California Agriculture (https://doi.org/10.3733/ca.v062n03p97).

UCCE Master Gardener Participation

In the initial trial, five of the 10 species that were evaluated maintained favorable performance throughout the season. Due to the wide range of California climates, researchers partnered with UC Cooperative Extension (UCCE) Master Gardeners (MGs) from around the state to evaluate successful plants from those trials in their own counties. Master Gardeners planted, tended, and collected data on selected plant material. In addition to tracking irrigation frequency, MGs collected aesthetic ratings to determine if plants had a wide-ranging appeal. Ultimately MGs in 14 counties participated in the project between 2009 and 2014 in 17 demonstration gardens in the cities listed below.

El Cajon Livermore Redding
Encinitas Madera Riverside
Fallbrook Mariposa Stockton
Fresno Palo Alto Sun Valley
Grass Valley Plymouth Thousand Oaks
Irvine Pt. Loma  

This portion of the UCLPIT was terminated after 2014 due to time and financial constraints.

Doubling Down

After the completion of the first trial, Karrie and Loren decided to replant the field with 6 additional natives to continue the research project. As the research progressed, interest in the project grew. In 2009, Ball Ornamentals became our first industry partner to submit plants to the trial, providing 10 varieties for evaluation. In response to continued interest in the project, Karrie and Loren developed the site to accommodate a second field, planted in 2012.

The evaluation of the plants requires two years with planting in the fall, establishment during the first summer, and the application of the deficit irrigation treatments and plant performance evaluations taking place during the second summer.  Due to the two year cycle of the trials, utilizing two fields that are planted in alternate years allows the opportunity to have a portion of the field undergoing the deficit evaluation each year.  In 2012, the trials transitioned to all plant material evaluated being submitted by industry cooperators.

Getting Shady

In 2009 another graduate student, Carolee Trimble, joined Dr. Oki's lab group and focused on applying the trials protocol to shade conditions. To evaluate plant material that prefers some shade, a structure was constructed and covered with commercial shade cloth providing 50% shade. Carolee evaluated five taxa in Davis, which were also planted in 11 MG demonstration gardens throughout the state for further evaluation.

Spreading South

Since California is a large state with a wide range of climatic regions, in 2017 the researchers obtained funding from the California Department of Agriculture’s Specialty Crop Block Grant Program to replicate the trial fields in southern California. Researchers partnered with Dr. Darren Haver, a UCCE Advisor in Orange County and Director of UC ANR South Coast Research and Extension Center (South Coast REC) to develop a trial site at the REC in Irvine, CA. A grant from the California Association of Nurseries and Garden Centers (now Plant California Alliance) provided funding to replicate the 50% shade trials at South Coast as well. In addition to providing irrigation recommendations for a different climate region and soil type, replicating the trials at South Coast REC has allowed researchers to evaluate plant performance when irrigated with reclaimed water.