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Organic herbicides for weed control in urban landscapes
Weed management in landscaped areas can be challenging. Weeds may need to be controlled for public safety, fire reduction, aesthetics, and elimination of harborage for other pests. While many non-chemical options for controlling weeds exist—such as physical removal with tools, steam, flame or...
Your water-efficient landscape doesn’t have to be barren
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/
Save trees first: Tips to keep them alive during drought
Trees essential to lowering temperatures, cooling ‘heat islands'
Water restrictions prompted by the drought are driving Californians to prioritize how they will use their limited water. Because landscape irrigation is a major water use for many households, residents are looking outdoors to conserve water.
When choosing which landscape plants to save, “trees come first,” said Janet Hartin, UC Cooperative Extension area environmental horticulture advisor for San Bernardino, Los Angeles and Riverside counties. “Healthy communities need trees. Fortunately new California water restrictions allow for provisions to ensure trees receive adequate water to stay alive and healthy.”
“Mature trees are instrumental in cooling urban heat islands and we can't afford to lose them and start all over,” Hartin said. “Shade from mature trees can reduce surface temperatures by as much as 65 degrees in asphalt-covered parking lots. Shade from a single tree can reduce these surface temperatures from 165 to less than 100 degrees when air temperatures reach 110 degrees. Even with air temperatures in the 90s, surface temperatures can reach 140 degrees.”
In addition to providing shade, trees absorb and store carbon dioxide, release oxygen, enhance pollinators and wildlife habitat, filter pollutants from air and water and can reduce energy use, according to Hartin. Because trees take years to grow, they aren't as easily replaced as other plants.
As residents let lawns go brown, she recommends watering trees that are near or surrounded by lawn.
“If a tree is in the middle of a lawn, it is almost certainly watered by lawn irrigation,” Hartin said. “If it's not on a separate drip system, drag out a hose and allow the water to slowly trickle into the soil early in the morning or in the evening. Deep watering for two hours once every couple of weeks will keep most established trees alive."
In most jurisdictions, watering restrictions do not apply to hand watering and hand-held watering devices such as hoses, which may be used for longer periods of time than the restrictions permit otherwise. However, watering may be restricted in all cases to prescribed times of day.
“Check to see if your jurisdiction also requires a hose shutoff valve,” Hartin said.
“For fruit trees, we may have to forgo fruit production for a year or so. There may not be enough water to support fruit production, but the goal is to keep the trees alive during the drought,” she said.
She recommends watering trees away from the trunk, halfway between the trunk and the dripline – where the foliage ends and rain drips off the leaves – because “roots grow outward quite a distance as well as downward. Leave the hose on so the water is just trickling out,” she said. “You want water to seep into the soil and encourage the roots to grow deeper. The slow water flow will seep down a foot or so and the roots will follow, which will help anchor the tree. Move the hose around every half hour to hour in quadrants around the tree for more even watering.”
Don't have time to move the hose? Hartin suggests getting a soaker hose and wrapping it in concentric circles 2 to 3 feet apart.
“Soaker hoses are made from recycled tire rubber and allow water to slowly ooze out of the pores along the hose, distributing the water fairly evenly throughout the hose length. Avoid using soaker hoses longer than 75 feet due to pressure issues.”
To reduce evaporation around the tree, spreading mulch a few inches from trunk can help.
“Dark mulches can heat the environment so it's best not to use them,”Hartin said. “If you are in a fire-prone area, don't use organic wood-based mulches because they are flammable. Use decomposed gravel or pebbles, rock-based products instead. To keep sunlight out and discourage weeds, large wood chip mulches should be maintained 3-4-inches deep and smaller inorganic mulches at 1-2 inches.”
Residents may want to maintain some grass for children and pets because bare feet and paws can sustain serious burns on surfaces hotter than 120 degrees.
“People don't realize how hot fake grass can get,” Hartin said. “Research I conducted last summer in the Coachella Valley and Redlands found that surface temperatures of synthetic lawns can be more than 65 degrees higher than living turf and groundcover surfaces on several dates in between May and August.”
For California lawns, there are drought-tolerant grasses that can thrive on 30% less water than bluegrass and other cool season varieties. Examples are buffalograss and bermudagrass. They still require maintenance, such as mowing, but are great for play and recreational surfaces for people and pets.
Jim Baird, UC Cooperative Extension turf specialist based at UC Riverside, said, “Turfgrasses offer numerous recreational, aesthetic, and environmental benefits including player safety, property value, mental health, erosion control, groundwater recharge and surface water quality, organic chemical decomposition, carbon sequestration and environmental cooling.”
There are also non-turf groundcovers that are drought resistant.
“As they transpire, plants cool the environment. We have more and more drought-resistant alternatives to high-water-requiring plants on the market now, and that's where we should be going,” Hartin said.
For people considering replacing their lawns and adding new landscape plants, she recommends planting low-water using groundcovers in the fall.
“It's too hot to plant in summer and even native and drought-resistant plants require water several times week until they get established,” she said.
Most counties have a UC Master Gardener Program with a helpline staffed by well-trained volunteers dispensing advice to help keep plants alive and recommend plants that are well-suited for the local environment. Find a local UC Master Gardener Program at https://mg.ucanr.edu/FindUs.
University of California Cooperative Extension
Drought and Landscape Tree Care Resources
Keeping Plants Alive Under Drought and Water Restrictions (English)
https://anrcatalog.ucanr.edu/pdf/8553.pdf
Mantener las plantas del exterior vivas con poca agua (Spanish)
https://anrcatalog.ucanr.edu/pdf/8628.pdf
Prioritizing Trees Under Drought and Water Restrictions (5-minute video)
https://www.youtube.com/watch?v=CTKLlJgdLVk
Tips to Keep Your Landscape Trees Alive During Drought
Landscape Tree Irrigation to Maximize Tree Health, Benefits, and Beauty
Landscape Tree Irrigation 101
Top 10 Ways to Conserve Water in Your Landscape and Garden
Use of Graywater in Urban Landscapes in California
https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8536
UC Master Gardeners ‘Garden Walks’ conserves millions of gallons of water annually in Marin
The Marin Municipal Water District has saved nearly 30 million gallons of water since it initiated a partnership with UC Cooperative Extension's Master Gardener program in Marin to teach residents how to conserve water.
The program, Garden Walks, was established in 2008 to help Marin conserve water in a district with limited supply. MMWD purchases about 75% of its water from reservoirs on Mt. Tamalpais and in west Marin, and the rest from Sonoma County's Russian River water system.
Garden Walks provides personalized information and advice to water district customers focused on improving their irrigation practices to conserve water. The part-time coordinator sets up about 150 appointments a year for UC Master Gardener volunteers to visit the homes of Marin County residents and teach them how to manage their outdoor water usage with conservation in mind.
“When we finish our visits, I hope that the client is more confident about being proactive in their garden,” said Pam Polite Fisco, the program coordinator. “We hope they will be saving water, will use natives and will encourage wildlife in their gardens.”
The volunteers, dispatched in pairs, spend about an hour at the homes. They walk the garden and talk with residents about grouping plants with similar water requirements, adding mulch to the soil surface and composting clippings, leaves and other green waste so it stays on the property.
The UC Master Gardeners teach the residents how to check their water meters and use the meter to help determine whether there are leaks in the system. They provide advice on water-conserving plants, such as natives or other drought-tolerant plants. They ask the residents to run their sprinklers and other irrigation systems to ensure they know how to manage the controls.
The majority of the water savings realized by the program stems from repairing leaks and cutting back on overwatering, said Steven Swain, UC Cooperative Extension horticulture advisor and the technical advisor to the Marin County Master Gardener program.
As part of their agreement with UC Cooperative Extension, the Marin Water District monitors changes in water usage and reports them annually on their website, allowing Swain to determine the program's impact.
The majority of water savings during the life of the program is attributable to just one quarter of the houses Master Gardeners visited; three quarters of participants were managing water sustainably.
“Sometimes, our volunteers just give the residents a pat on the back and compliment them for a job well done,” Swain said.
About 6% of the clients visited have hidden water leaks in their irrigation systems. These leaks can waste huge amounts of water if not caught, and account for a large portion of the water savings. Another 18% of clients are overwatering, which accounts for much of the rest of the savings.
Considering the value of the water conserved by the Garden Walks program, the $40,000 annual cost to hire the coordinator is more than offset by the reducing amount of water the district must provide.
This program has received a number of awards, including the Marin Conservation League's Ted Wellman Water Award in 2010. In 2011, it received first place in the UC Master Gardener's Search For Excellence awards and the Community Outreach Award at the National Extension Master Gardener Coordinating Conference. Marin County residents have also praised the program.
“The Master Gardener team was friendly, professional and helpful and shared their positive attitude to their garden and their outreach,” said Fairfax resident ‘Julie' in a follow-up survey
‘Jean' of San Rafael said, “I'm a beginning gardener. They helped me figure out how to start off right.”
A number of California counties were inspired by the success of the Marin County Garden Walks program and have adopted similar efforts to visit homeowners and assess irrigation efficiency.
View a video about the Marin Garden Walks porgram:
Meet Emily Meineke, New UC Davis Urban Landscape Entomologist
While you're sheltering in place due to the coronavirus pandemic precautions, not too many people are aware of a new faculty member in the UC Davis Department of Entomology and Nematology, recently arrived from Harvard. Welcome, Emily Meineke! She joined the UC Davis Department of Entomology and...
These redhumped caterpillars, to become moths, Schizura concinna, family Notodontidae, are dining on the leaf of a Western redbud, (Cercis occidentalis) in Vacaville, Calif. Emily Meineke, newest faculty member of the UC Davis Department of Entomology and Nematology, studies how climate change and urban development affect insects, plants, and how they interact with one another. (Photo by Kathy Keatley Garvey)
