Guest author Jodie Cook, ASLA, SITES AP, is President of  Jodie Cook Landscape Design , in San Clemente, California. She takes us on a plant performance research journey as an evaluator. In addition to landscape design and program management, Jodie teaches The Sustainable Landscape and Native Garden Design at Saddleback College. Jodie also serves as a leader for ASLA’s  Planting Design Professional Practice Network (PPN) . The Credential provides an excerpt of Jodie's article here. 

As a horticulturally obsessed landscape designer for most of my adult life, I’ve observed how our landscape irrigation practices, tools, and technologies have evolved over time. In the last few decades, we have radically changed our plant irrigation practices in public and private designed spaces, particularly in the West. While using a plant palette of so called ‘drought tolerant’ species, many large commercial landscapes, and managed communities such as mine, irrigate four times per week or more in a climate that has never experienced rain with such frequency. I have often wondered, why do we irrigate non-lawn areas so much?

 

So, I was thrilled to be a participant in the Climate-Ready Landscape Plants trial evaluations at the University of California South Coast Research Center fields in Irvine, California. I was a plant performance evaluator and was not involved in the research in any other way. I discussed the research at length with those who devised the trial.

This trial is a long-term irrigation deficit study initiated in 2004 by then-graduate student and most recently UC Cooperative Environmental Horticultural Advisor Karrie Reid in collaboration with universities throughout the western states. The original growing fields were located on the campus of UC Davis in Northern California. The study has now evolved to include southern California and additional fields in Arizona, Oregon, Washington, and Utah.

Click to review the complete Plant trial evaluation rubric, University of California Climate-Ready Landscape Trials 

This long-term plant evaluation project is a deficit irrigation trial occurring in states that often suffer from drought conditions of historic proportions. Researchers are discovering exactly how far below reference evapotranspiration rates ornamental plant species can go while preserving their aesthetic qualities. This means scoring as close to 5 on the trial’s 1 to 5 multivariate scale as possible. As sustainability-focused landscape architects and designers, how little can we irrigate our landscapes to maintain high aesthetic performance? Not as much as we do right now.

Growers selected common landscape species—shrubs, perennials, and grasses—that revealed unexpected drought resistance. The researchers confirmed that some of these species were very low water users, but that with the correct soil preparation, irrigation frequency and duration, plus maintaining a three-inch layer of wood chip mulch on top of the soil, many other plants could be drought resistant, too. 

The unique aspect of this ongoing trial is in how irrigation is applied. It is a reduction in watering frequency over time, allowing the soil to dry to a specific level based on site soil texture before topping it up fully and allowing this oscillation to dictate ongoing watering frequency.

Recently, weather-based controllers were manufactured to easily allow longer intervals of up to a month or more between watering events.  Irrigation is often delivered as a reduced percentage during each weekly set of irrigation run times—a reduced duration occurred, but the weekly frequency remained. For many low-water plants (especially natives), this is not an ideal arrangement. It can lead to crown rot, invasion by pathogens, salt accumulation in soil, and to a significant waste of water over time.

The UC Climate-Ready Landscape Plants trials used a different method. After a one-year establishment period when plants were watered regularly at 25% root zone moisture depletion to foster healthy growth and a deep root system, the researchers began to alter the frequency of irrigation based on localized evapotranspiration rates. Irrigation frequency decreased slowly so plants would adapt by growing deeper roots to access soil moisture. Then, plant root zones were allowed to deplete 50% of plant available moisture. At each irrigation, that 50% was reapplied to refill the root zone volume calculated as 1m (3.3 ft) wide, by .5m (1.6 ft) deep for the trial’s primarily shrub species. The plants were not irrigated again until 50% of the root zone was depleted. Evapotranspiration rates were calculated daily but accumulated until the 50% depletion rate was achieved before irrigation was applied. The studied plants were a mix of common landscape species such as roses, larger flowering shrubs, and flowering groundcovers.

Three water requirements are used in the trial program: High (80% ETo), Moderate (50% ETo), and Low (20% ETo). The resulting irrigation frequency in the dry Mediterranean climate of my region revealed high water plants needing irrigation approximately every 10 days between April and October, and the low water plants every 51 days. The high-water plants required 26.9 inches of water, and the low water plants required just 6 inches. During the study period, our region enjoyed just 1.56 inches of natural rainfall, and the trial fields are in full sun under varying soil conditions.

It is relatively easy to calculate irrigation in this way. Water plants deeply, infrequently, and use sustainable technology and methods. Let’s remember these lessons from the University of California Climate-Ready Landscape Plants trials.

NOW DELIVERING: 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If your license renews on your date of birth this month, or by state requirement when your license origination occurred, or any other jurisdiction imposed requirement, it's time to renew.

 

Contact us to receive a sample custom monthly credentials report containing:

 

1.

All A/E/LA national and international licensure status with renewal dates

 

2.
Professional affiliation membership types with renewal dates

 

3.
Current multi-discipline continuing education requirements needed

 

4.
 Comprehensive recorded history of categorized education credits

Learn more about our innovative and easy-to-use service at: AECredentialing.com.

 

 Contact Details:

LS Credentialing Services LLC

WBE Certified

P.O. Box 91

Olathe, KS 66051

Lexi@AECredentialing.com
913-608-7880