- Author: Saoimanu Sope
UC climate-ready landscape trials identify low-water yet attractive plants
Good news: roses can be a part of your water-efficient landscape. Lorence Oki, UC Cooperative Extension environmental horticulture specialist in the UC Davis Department of Plant Sciences, identified rose cultivars that remain aesthetically pleasing with little water.
Oki is the principal investigator of the Climate-Ready Landscape Plants project, which may be the largest irrigation trial in the western U.S., and the UC Plant Landscape Irrigation Trials (UCLPIT), the California component of that project. These projects evaluate landscape plants under varying irrigation levels to determine their optimal performance in regions requiring supplemental summer water.
“There are some assumptions that pretty plants use a lot of water, like roses,” Oki said. “Everyone thinks they need a lot of water, but we've found some that don't, and they still look great. A water-efficient landscape doesn't need to look like a Central Valley oak-grassland in the summer. It can look really attractive.”
In 2021, Oki's team at UC Davis identified Lomandra confertifolia ssp. pallida "Pom Pom" Shorty and Rosa "Sprogreatpink" Brick House® Pink as two of the best low-water plants in the trial.
“The useful tip or information that is shared at the end of each trial is the selection and designation of plants as Blue Ribbon winners. These are the plants that looked good with an overall rating of 4 or higher throughout and were on the low (20%) water treatment,” said Natalie Levy, associate specialist for water resources, who manages the project at the UC ANR South Coast Research and Extension Center.
How plants earn a blue ribbon
Each trial year, the selection of new plants is based on research recommendations and donated submissions from the nursery industry. The landscape plants are trialed in full sun or 50% shade cover.
Irrigation treatments are based on the rate of evaporation and plant transpiration (evapotranspiration) measured through a local California Irrigation Management Information System (CIMIS) weather station that provides a reference evapotranspiration (ETo) rate.
Three levels of irrigation are provided to the plants equal to 20%, 50%, and 80% of ETo. The volume of water applied is the same at each irrigation based on soil characteristics, but the interval between applications varies with weather and the treatment. Using this method, irrigations for the 20% treatment are less frequent than the 80% treatment.
“The 20% treatment during the 2022 trial was irrigated an average of once per month while the 80% treatment was irrigated weekly,” explained Levy.
During the deficit irrigation trial, monthly height and width measurements are taken to determine the plant growth index. Monthly qualitative aesthetic ratings on a scale of 1 to 5 are determined for foliage appearance, flowering abundance, pest tolerance, disease resistance, vigor and overall appearance.
A second round of flowering abundance and overall appearance measurements are also taken to capture more of the blooming period. For example, UCLPIT identified in the 2020 trial at South Coast REC that the "Apricot Drift" rose had a mean overall appearance score of 3.5 out of 5, deeming it “acceptable to very nice” and a low water use plant within the Water Use Classification of Landscape Species or WUCOLS guide.
Project expands options for landscape planting
“(WUCOLS) only has 3,500 plants in it. There are guesses that there are close to 10,000 cultivars in urban landscapes in California, if not more,” said Oki. “WUCOLS also didn't have numerical ratings. Instead, you'll see verbal ratings like ‘low water use' or ‘high water use.'”
The UCLPIT project has not only developed numerical recommendations for irrigation, but it has also added new landscape plants that are compliant with California's Model Water Efficient Landscape Ordinance. In fact, UCLPIT's data is one of the few sources that can be used to supplement WUCOLS.
Geographic diversity of trial sites adds to knowledge base
In addition to UC Davis and South Coast REC in Irvine, the trials have expanded beyond California as the Climate-Ready Landscape Plants project and is in progress at Oregon State University, University of Washington, University of Arizona and Utah State University thanks to a USDA/CDFA grant awarded in 2020.
Lloyd Nackley, associate professor of nursery production and greenhouse management at Oregon State University, is the principal investigator of the trial in the Portland metro area, which is entering its third year.
“People know that there are drought tolerant plants, but there are many. We're trying to highlight lesser known or newer varieties. And even though the trial is three years, most gardeners would hope that their garden lasts longer than that,” said Nackley.
One of the observations that Nackley recalls is of the Hibiscus Purple Pillar plant. Unlike the trial at South Coast, the Purple Pillar did not perform well in Oregon in the spring.
“It wasn't until August that we saw the plant bloom and begin to look like what we saw from South Coast in April,” Nackley said.
Ursula Schuch, horticulture professor and principal investigator of the trial taking place at the University of Arizona, was also surprised at the range of performance among different plant types and the effects of irrigation, heat and temperature.
“This research will reassure green industry professionals that they can stretch their water budget to successfully cultivate more plants, watering them according to their needs instead of irrigating every plant according to the highest water-using plants,” said Schuch.
Although research is only conducted in the West, the hope is that there will be trials in other regions of U.S.
Doing so would yield comprehensive information about the plants and their performance in different climates. As extreme weather events persist in the U.S., disease pressure and risks do too. Trials throughout the country would provide location-specific data regarding disease susceptibility.
To learn more about the UCLPIT research project, visit https://ucanr.edu/sites/UCLPIT/
/h3>/h3>/h3>/h3>- Author: Pamela Kan-Rice
Karrie Reid didn't plan to become a scientist, but she fell in love with plants. Reid, who joined UC Agriculture and Natural Resources as the UC Cooperative Extension environmental horticulture advisor for San Joaquin County in 2010 with funding from the county's Public Works Solid Waste Division, retired Sept. 30.
Reid, who was born in Jackson in Amador County, earned her bachelor's degree in biology from UC Santa Cruz and her master's degree in horticulture and agronomy from UC Davis. She has written nearly 100 articles on – and trained hundreds of people in – sustainable urban landscape management.
“I wasn't much interested in biology in high school,” Reid said, “but after taking a botany class at San Joaquin Delta College, I fell in love with plants and subsequently took every class related to plants I could find both at Delta and UCSC.”
“After spending several years teaching and raising my children, I decided to go back to school for my graduate degree mostly because I saw such a great need for better planning and management in urban landscapes.”
While working on her graduate degree, Reid began assisting Loren Oki, UC Cooperative Extension landscape horticulture specialist in the UC Davis Department of Plant Sciences, on two projects related to landscape water conservation and quality.
For one of those projects, she identified chemicals in urban runoff water from single-family homes and educated homeowners on practices to reduce pollutants sent to local waterways. In the other, she ran irrigation and climate zone trials on landscape ornamental plants in Northern California at UC Davis and Southern California at UC South Coast Research and Extension Center in Irvine.
As a UCCE advisor, Reid has continued to collaborate on the UC Landscape Plant Irrigation Trials project, sharing the results with UC Master Gardener volunteers, landscape professionals and home gardeners, who use the water use and climate performance data to select their plants. Because about half of urban water in California is used for landscape irrigation, the plant varieties chosen can help conserve water.
When asked what stands out looking back on her career, Reid said, “I feel most proud of my role in the UC Landscape Plant Irrigation Trials because it has reached so many people and had such a high impact for the nursery and landscape industries. We had a lot of detractors, but we continued to pursue it because we believed in it. It has been a powerful vehicle for raising awareness and changing practice around urban landscape water conservation.”
Reid and Oki received nearly $1 million in 2020 from the CDFA/USDA Specialty Crops Multistate Program to fund a new Climate Ready Landscape Plants project, expanding the research trials to Washington, Oregon, Utah and Arizona. She is currently finishing up that research and the results will help people in the other Western states make informed decisions to select low water-use landscape plants.
In 2020, when the county considered redirecting funding for Reid's salary as a UC Cooperative Extension advisor to cover new mandates, several people who had collaborated with Reid over the years wrote letters urging the county to continue funding her position.
One of her supporters was Todd Rocha, Parks and Recreation superintendent for the city of Tracy.
“When I reached out to the UC Cooperative Extension for assistance with an issue in a streetscape, Karrie responded,” Rocha wrote. “Upon her arrival, it became immediately evident she is knowledgeable and eager to share that knowledge. As an added result to the solution she offered that day, we coordinated a landscape irrigation seminar in which she presented basic irrigation principles in a manner that was straightforward and understandable by my maintenance staff.”
Pleased with Reid's seminar, Rocha arranged for her to provide Green Gardener training to City of Tracy's parks staff and school ground staff. Green Gardener's environmentally friendly landscape practices conserve water, prevent polluted runoff, divert green waste from landfills and use best management practices to care for grass, shrubs and trees. After the training, the city diverted thousands of yards of chipped tree trimming to be used as mulch.
“What they are learning in this program will improve the conditions of our sites, make the facilities safer and just as importantly – help us protect and conserve resources,” wrote Don Scholl, Tracy's Public Works Department director.
Reid said, “I am also quite satisfied with the Green Gardener Training I put together for landscape maintenance professionals and the large number of folks in the industry that educational program has helped during my relatively short career with UCCE.”
Timothy Pelican, agricultural commissioner in San Joaquin County, wrote: “The job she does in helping gardeners understand the use of integrated pest management helps to protect our air and waterways from unnecessary pesticide exposure. In San Joaquin County, runoff from improper pesticide use oftentimes ends up running off into the Delta, endangering both people and wildlife.”
Steve Dutra, president of Tree Lodi, wrote that he has attended several of Reid's workshops. “As a certified arborist, I have relied on this advisor numerous times,” Dutra wrote. “It is a known fact that not everyone can know everything in their given profession. From my prospective, having the expertise and experience available is of great value.”
Farmers also voiced appreciation for Reid. Jerry Barton of Ripon worked with her to recycle his orchards by chipping trees for mulch rather than burning the wood.
“In Karrie Reid you have an exceptional person working as our environmental horticulture advisor in San Joaquin County,” Barton wrote to the Solid Waste Division. “On numerous occasions I have called on her for advice. She is always prompt in her response and I have even received her counsel after normal business hours. She represents the very definition of an exceptional public servant.”
- Author: Ann Filmer
A research project initiated in the Department of Plant Sciences at UC Davis evaluates landscape plants in two-year trials under varying irrigation levels to determine the best irrigation level for optimal plant performance in regions requiring supplemental summer water. Creating water budgets is required by California's Model Water Efficient Landscape Ordinance (MWELO), and the results from these research trials help landscape professionals and home gardeners make informed decisions when specifying, selecting or promoting low water-use landscape plant material.
This year, the CDFA/USDA Specialty Crops Multistate Program funded a new Climate Ready Landscape Plants project, which will replicate the successful fields that are currently installed at UC Davis and UC ANR South Coast Research and Extension Center in Irvine.
Loren Oki, UC Cooperative Extension specialist in the UC Davis Department of Plant Sciences, is the lead principal investigator and collaborators include researcher Jared Sisneroz; project leader Karrie Reid, UC Cooperative Extension environmental horticulture advisor in San Joaquin County; and Darren Haver, UC Cooperative Extension water resources and water quality advisor and director of South Coast REC and UCCE in Orange County.
Under Oki's oversight, this new $999,992 grant will support the development of additional fields at several western universities:
- University of Washington, Soo-Hyung Kim
- Oregon State University, Lloyd Nackley and Ryan Contreras
- Utah State University Center, Youping Sun and Larry Rupp
- University of Arizona, Ursula Schuch
Conducting these new experiments on landscape plants at diverse sites across the western U.S. will reveal differences in recommendations since irrigation guidelines for landscapes vary depending on climate and soil type.
The initial project was initiated as Reid's master's degree thesis research in 2004, with Oki as her major professor, and has been ongoing since then.
Project descriptions, results and images can be seen at the UC Landscape Plant Irrigation Trials website at https://ucanr.edu/sites/UCLPIT.
- Author: Karrie Reid
Did you ever wonder how that latest plant variety made its way to your local nursery? Few people outside of the plant breeding and marketing industry realize that the “new” plant you just saw at the garden center last weekend actually began its journey from 6 to 20 years earlier 1 . One of the last steps in that journey is the plant trial.
Plant trials take place all over the country at universities and public gardens and are usually the last step before a company decides to launch a new cultivar onto the market. Although they will have evaluated a promising new cultivar in a company field, the information received from a third-party trial has the advantage of being unbiased. Those plants that prove themselves novel, attractive, and hardy are then branded and put into the latest catalog.
Focus on sustainability
The vast majority of university and botanical garden or arboretum trials are designed to provide ideal growing conditions— ample water and fertilizer — to maximize the potential of the plants. At the University of California, Davis, we go about plant trials in a completely different way. Our goal is to reveal the best perennial plants for sustainable landscaping in the increasingly hot and dry West.
What we promote with the UC Landscape Plant Irrigation Trials, or UCLPIT, is gardening with plants that are suited to their environment without the need for fertilizers, pesticides, or excessive amounts of water. Plants that make it through our trials with a high score can be counted on to be beautiful, low maintenance, and low water users, our Blue Ribbon™ winners, or moderate water users, which we designate Happy Mediums™.
Plants on trial
The unique thing about this trial is that plants are given several different irrigation treatments (high, moderate, or low) and evaluated for performance on each. 2 While other trials typically evaluate from 3 to 5 individuals of a new cultivar all under the same conditions, we evaluate 24, with 8 plants on each weather-based irrigation treatment.
Plants are placed in randomized complete blocks in the ground, established on regular water in the first year, and evaluated on the different irrigation levels in the second year. Monthly measurements and quality ratings give us a good picture of how the plants perform and whether there are differences caused by the amount of water they receive. This robust scientific method over two years means we can perform statistical analysis and determine with a good degree of certainty the actual water needs of a particular cultivar.
Looking at them for two years affords the opportunity to see how they handle the mild frost and strong breezes we receive in Davis. We can also assess what kind of maintenance they require to keep their good looks. We do provide winter pruning too many of our shrubs and most of the grasses, but we make a point not to be too “precious” about it; we are trying to think like a commercial landscaper and imitate what they would probably do. With over 500 plants in the ground, anything requiring more than annual trimming is just too much work! For instance, with groundcover roses, we take power hedge trimmers to them and just whack them back to a consistently small mound, without paying attention to outward-facing buds.
Low water use vs. drought tolerant
Drought tolerance really just means that a plant will survive without water for some period of time. However, there are plenty of these survivors that look hideous without regular water and are not desirable to the average gardener. Few people want a garden that appears to be barely hanging on to life.
To be good for sustainable landscaping, a plant must not just survive, but thrive and still be attractive on low or moderate water. So, while we are evaluating plants for water use, we are also looking at a variety of aesthetic and health parameters:
- Foliage quality: does it wilt or curl up in the midday sun? Is it healthy and uniform?
- Pest and disease damage: is it more or less susceptible based on water availability?
- Flowering period and abundance: is the bloom affected by water; is it a flash-in-the-pan or lackluster bloomer; or does it re-flower or flower over a long period of time?
- Vigor: does it languish or continue to grow?
- Visitation by pollinators and beneficial insects: is it providing added ecosystem benefits?
- Most importantly, the overall landscape appearance — the WOW factor: do I see this from across the field and think, “What is that plant?” It does a plant no good to be classified as a low-water user if no one wants to buy it.
Some surprises
One of the best things about plant trials is that they have the potential to shatter your preconceived ideas about plants. One of the most fascinating things to me has been just how many of the plants we have evaluated performed equally well on all irrigation treatments. This suggests that most people over-water or water too frequently. Our highest irrigation treatment is watered once a week during the middle of July and less often in the shade.
From a scientific standpoint, when plant growth is virtually identical on all irrigation treatments, it means that many genera have evolved the ability to grow only so much during a particular growing season, regardless of the availability of water. Additional water may actually be a disadvantage if not used. If the soil is heavy and water cannot drain below the root zone, it may set up an unhealthy root environment. The water is then not only wasted but detrimental.
My realization of the power of research to disprove our assumptions came in the very first trial where we evaluated San Diego sedge, Carex spissa. At that time, the current edition of Sunset Western Garden Book stated that it required “ample moisture”. Given that it was a riparian/bog species, that was a fair assumption. However, we showed that with one year of regular water for establishment, it was actually able to perform quite well on low water; plants that were irrigated only twice during the summer looked just as robust and healthy as those that received the high-water treatment. When you consider the fluctuating nature of California's water supply, the evolution of the ability to handle both inundation and drought seems quite advantageous, making Carex spissa an excellent choice for vegetated swales.
One of the critical things to bear in mind with new introductions is that plant breeding brings new genetics into known plant genera. While they are adding a flower color or leaf shape or plant size, there may be something hitchhiking along in the genome that alters previous water use habits for better or worse. By evaluating new plants under different irrigation regimes, we have revealed both sides of this equation. For example, we have seen both rose and butterfly bush cultivars that performed best on low water, while others required moderate or high for best performance. Clearly, we cannot assume that a new cultivar will have the same adaptations as previously-known varieties.
Open house
One of the ways we assess the appeal of these potential introductions to the market is by holding Open House ratings events three times a year: spring, summer, and fall. We invite landscape and nursery professionals and academics, garden writers, public agency personnel, and UC Master Gardeners to view the second-year plants undergoing irrigation treatments and rate a sample of them on a limited number of characteristics. We also invite feedback on favorite plants, plants they would use, and plants they dislike. We share this information with our cooperators who have entered the plants into the trials so they can make decisions about whether or not to advance plants to market, at least in our region.
Looking ahead
For the entire life of UCLPIT, grant funding has played a major role in allowing us to provide this program to the industry and the gardening public. Our most recent grant from the U.S. Dept. of Agriculture and the California Dept. of Food and Agriculture is allowing us to partner with academic colleagues at universities in Washington, Oregon, Utah, and Arizona to replicate our trials in their locations. They will work with industry partners in their regions to identify and evaluate plants appropriate to their sites.
Three years ago, we took the leap and replicated our trials for both sun and shade in Southern California at the UC South Coast Research and Extension Center (REC) in Irvine under the direction of Dr. Darren Haver. This allows us to evaluate plants in this very different climate zone and soil type (sandy loam).
Additionally, the REC uses reclaimed water. Since many parts of Southern California are now using reclaimed water for landscape use, it will be critical to know if potential introductions can tolerate it.
We know that the trend toward sustainable landscaping has spread across the country and believe that Step One is knowing which plants are regionally appropriate. We are excited about bringing the scientific rigor of our plant trials process to other regions and hope that wherever water availability is a factor, this model of plant evaluation becomes the norm. With so many beautiful plants in development and now available for the sustainable gardening model, we are thrilled to be part of the process that brings an ever-wider variety of new and exciting climate-appropriate plants to a garden center near you!
If you fit into the category of one of our Open House participants and would like to attend one of our events, please contact us for more information.
Visit the UC Landscape Plant Irrigation Trials website and Facebook page.
1 The UK Plant Breeding Sector and Innovation https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/552498/Plan t-breeders.pdf
2 For a more detailed description of our irrigation protocols, please visit our website: https://ucanr.edu/uclpit
This article was originally published on the Pacific Horticulture Society website.
/span>/h3>/h3>/h3>/h3>/h3>/h3>- Author: Jeannette E. Warnert
San Joaquin County UC Cooperative Extension in Stockton maintains pesticide-free roses as one of two trial sites in California for the American Rose Trials for Sustainability, reported Angelina Dequina in the Daily Titan. The other California location is at California State University, Fullerton.
Since 2012, the American Rose Trials for Sustainability has conducted scientific research to determine the best rose cultivation techniques for gardeners in each region of the U.S. The roses in the trial plots are grown with minimal care; the only inputs are water and compost. The San Joaquin County roses are maintained by UC Master Gardeners in the UCCE Learning Landscape, which beautifies the Robert J. Cabral Agricultural Center and features a series of small, themed, climate-appropriate gardens.
The Learning Landscape is used for educational Open Garden Days and to teach a variety of workshops for landscape professionals. The public is welcome to stroll the gardens seven days a week during daylight hours. The facility is at 2101 E. Earhart Ave. in Stockton.
Project lead Karrie Reid, UCCE San Joaquin County environmental horticulture advisor, said the rose trials are integral to the marketing of rose cultivars, according to the Daily Titan article.
Once the two-year trial ends, the trial gardens may keep the roses they planted.