- Author: Jeannette Warnert
Facing costly water bills and stringent municipal water limits, some Fresno County residents and businesses are opting to replace their lawns with synthetic grass. However, research by UC Cooperative Extension environmental horticulture advisor Janet Hartin has found that fake lawns have significant drawbacks.
To begin with, synthetic lawns are superheating what are already urban heat islands like those found in Fresno County. In the City of Fresno, for example, the average summer temperature is 4° F higher than in rural areas due to the urban heat island effect. (CalEPA)
Hartin conducted her research in Palm Springs and Redlands. While average summer temps are 5 to 10 degrees higher in Palm Springs than in Fresno, temperatures in Redlands are very similar. Hartin measured the surface temperatures of synthetic lawns, black mulch, asphalt and plants between 3 and 3:30 p.m. on several dates between May and August for the last three years.
“The surface temperature of asphalt, synthetic lawns and black mulch were more than 65° hotter than plants in Palm Springs and 60° higher in Redlands,” Hartin said. “The highest temperature I recorded was 173 on synthetic turf in Palm Springs. Black asphalt adjacent to the synthetic turf got as hot as 170°.”
The surfaces of plants she measured for comparison – groundcovers, vegetables and turfgrass lawns – hovered around 90° to 95° in Redlands and 95° to 100° in the desert.
“Plants are so much cooler because of their transpiration, the process in which the plant releases water vapor back into the atmosphere, cooling plants and their surroundings. Non-living surfaces don't transpire, so they will never be as cool as a living surface,” she said.
The surfaces of concrete and light-colored mulches were warmer than living green areas, but not nearly as hot as surfaces of darker-colored materials.
More and more, sports fields are being converted to synthetic turf because of its durability and lower water and maintenance needs. However, the hotter surface when the weather is warm, and rigid base compared to the sponge-like quality of natural turf, has led to an increase in injuries, Hartin said.
“Managers of schoolgrounds, parks, playgrounds and sports fields in inland and desert communities should choose living grass over synthetic materials,” Hartin said. “Because of California water woes, the days of wall-to-wall grass in front and back yards should be behind us, but we don't want to get totally away from grass. Other alternatives to consider are drought-resistant groundcovers.”
Another concern is disposing of the fake grass when it is removed. According to the synthetic grass industry, the product is expected to last for 20 years. (Synthetic Turf Council) After that, it is difficult to recycle, so typically ends up in landfills.
Grass, on the other hand, is easy to recycle. Throughout California, mowed grass clippings – along with other green waste like leaves, prunings and leftover food - are being picked up separately from garbage and composted. The grass clippings play a key role in the quality of the compost produced by municipal recycling programs.
“Compost is best created when ‘browns,' like fallen leaves, are combined with ‘greens,” like fresh grass clippings, in a 50/50 ratio. After adding moisture and regular turning, the product is ideal for nurturing soil,” Hartin said. “Or, the clippings can be used as a mulch on the surface of soil to reduce weeds, conserve water and keep plant roots cool. You can't do that with fake grass.”
Grow plants instead
Hartin believes the best surfaces in front and back yards are living plants. Green living surfaces not only cool the environment, they provide habitat for pollinators and food for birds. Earth worms and healthy microbes break down organic matter under turf and groundcovers, which improves soil quality. Climate-appropriate plants also help reduce stormwater runoff and reduce soil erosion.
"The cooling and ecosystem benefits of growing plants outweigh their water and maintenance requirements," she said. “What we plant today is going to benefit the community for decades to come."
Read more:
In the valley, 'heat islands' of asphalt and fake lawn reach 170 degrees. What you can do, Janet Hartin, The Desert Sun
Once hailed as a drought fix, California moves to restrict synthetic turf over health concerns, CalMatters
Synthetic sports fields and the heat island effect, Sonia Myrick, National Recreation and Park Association Magazine
- Author: Saoimanu Sope
In a drought-prone region like Southern California, working with Mother Nature is not only wise but necessary, according to Janet Hartin, UC Cooperative Extension horticulture advisor for Los Angeles, San Bernardino and Riverside counties, who studies climate-ready trees.
In 2020, Governor Newsom launched the California Climate Action Corps, empowering Californians to protect their communities from the impacts of climate change. Newsom's call to action emphasizes the need for long-term and sustainable solutions like Hartin's research, which urges Southern California to care for existing trees and plant new ones.
In collaboration with the U.S. Forest Service and other UC Cooperative Extension scientists, Hartin is amid a 20-year research study identifying trees suitable for California's different climate zones. Her work provides a comprehensive understanding of trees and their benefits related to human and environmental health, particularly as Californians navigate climate change's evolving challenges.
One of these concerns is urban heat islands. UHIs are areas in which heat is reradiated from paved concrete or asphalt surfaces. In cities covered in asphalt, like Los Angeles, average temperatures can become six degrees hotter than surrounding areas.
To reduce urban heat islands, she has been working with community organizations to plant trees. In March, for example, Hartin teamed up with the Inland Empire Resource Conservation District to increase tree canopy in the Inland Empire.
Trees keep cities cool
To keep the city cool, some Los Angeles neighborhoods are repainting pavements with reflective coating. According to a 2020 study published in Environmental Research Letters, reflective coating can decrease pavement temperatures up to 10 degrees. As helpful as this is, augmenting urban landscapes to include heat-, drought- and pest-resistant tree species, whether native or not, can significantly reduce the impacts of urban heat islands too.
“Trees can cool impervious surfaces by 40 to 65 degrees,” Hartin said. During a 2021 study, in May and June Hartin discovered that unshaded asphalt could be more than 60 degrees hotter than shaded asphalt during late spring and early summer in inland and desert cities.
Other than providing shade, trees are effective at deflecting the sun's radiation and cooling the atmosphere through evapotranspiration. Given that they absorb and store carbon as well, trees lessen the impacts of pollution from fossil fuels.
“A well-tended mature landscape tree can absorb 40 tons of carbon over its lifespan,” said Hartin.
In a 2021 blog post, Hartin suggests trees be selected based on their adaptation to the “micro-climate” in each particular landscape, noting factors to consider like shade, proximity to buildings, space needs below and above ground, soil type and water source. She also recommends the Sunset Western Climate Zone maps for reference, noting that they are “more precise than USDA zones for our warmer climates.”
Based on the study with the U.S. Forest Service examining the performance of 12 species of underplanted but promising landscape trees at UC Riverside, favorable candidates include bubba desert willow and maverick thornless honey mesquite for their drought resistance, and red push pistache for its drought and heat resistance.
Tamara Hedges, executive director of UC Riverside Palm Desert Center and member of the Board of Directors for the Oswit Land Trust, agrees that trees are important in our fight against climate change:
“Through our partnerships with the UC California Naturalist and the Master Gardener Programs and many other nonprofits in the Coachella Valley, natural ecosystems are being protected and expanded and built environments cooled through the planting of appropriate tree species. These UC/USFS studies go a long way in identifying new underrepresented tree species."
General tips for planting
For California, planting in early fall through late winter provides ample time for trees to establish a strong root system before enduring the summer heat. Doing so also means that natural rainfall can fulfill water needs, as opposed to solely relying on irrigation systems.
Unlike newly planted trees, mature trees should be watered infrequently but deeply. Watering too often can reduce the level of oxygen in the rootzone and result in waterlogged soils prone to crown and root rots.
During the fall, trees only need about 15% of the water they would require in the summer. When watering, keep the tree trunk dry. Because the roots of the tree grow outward and are usually a foot deep into the ground, Hartin recommends watering the area around the trunk rather than the trunk itself. This will also help avoid water waste.
“Trees not adapted to the climate they're planted in and not receiving proper care are much more susceptible to invasive pests like shothole borers and diseases,” said Hartin. “Even the loss of one front yard tree can significantly reduce shade, increase the surrounding temperature, and diminish energy savings.”
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