- Author: Janet Hartin
ANR Environmental Horticulture (EH) academics develop and extend research-based information to producers and end-users of landscape, nursery, turfgrass, and floriculture plants. Our work focuses on optimizing the environmental, social, and economic benefits plants provide while conserving and protecting natural resources required for their production, use, and care.
Research and education we provide is aligned with the following ANR public value statements:
- Protecting California's natural resources
- Building climate-resilient communities and ecosystems
- Promoting healthy people and communities
- Developing a qualified workforce
- Developing an inclusive and equitable society
Our applied research and education is relevant to all five ANR Strategic Initiatives (Endemic and Invasive Pests and Diseases; Sustainable Natural Ecosystems; Sustainable Food Systems; Healthy Families and Communities; and Water Quantity and Quality).
Crucially, it impacts all urban Californians (95% of our population) by increasing the sustainability of our living urban environments and enhancing physical and mental health. We help remedy the historical inequality in the distribution of environmental benefits through research and education we extend to plant producers, arborists, park superintendents, landscapers, planners, community-greening non-profit organizations, and others supporting urban sustainability and environmental justice.
While our work is beneficial to all, it is especially critical in resource-limited cities, neighborhoods and communities most negatively impacted by climate-change.
Issues Adressed by ANR EH Academics:
Reducing Impacts of Climate Change in Our Cities. Properly selected and maintained urban trees, shrubs, and turf mitigate the impacts of climate change by cooling urban heat islands, reducing energy use, providing shade, and sequestering carbon dioxide. Trees reduce surface temperature of urban heat islands in inland and desert cities in California up to 20°C (68°F) and air temperatures up to 2.0°C (35°F). Due to climate change and urbanization, the rate, intensity, and duration of heatwaves in these urbanized areas are increasing, as is the number of heat-related deaths. Members of underserved and disadvantaged communities are at high-risk of experiencing health-related consequences of climate change, further exacerbated by living in neighborhoods with low tree canopy cover and hotter conditions. The poorest Californians are often the most impacted by climate change, leading to a form of endemic and prolonged social injustice.
Our applied research and education focuses on identifying heat, drought, and pest-resistant trees that withstand impacts posed by a warming climate and urban heat islands. Managers of trees in disadvantaged neighborhoods, parks, schools, and green spaces often lack resources to hire outside experts to assist them with proper tree selection and care, relying heavily (and sometimes exclusively) on our trusted, objective expertise. We provide location-specific, relevant and scientifically-supported information on complex technical issues related to horticulture, arboriculture, water management, and policy. Our technical expertise helps the green industry produce and properly maintain landscape trees and shrubs best equipped to perform under the pressures of climate change and mitigate its impacts. Our work directly leads to cooler, more habitable communities and neighborhoods, demonstrating our important role supporting environmental justice and climate change mitigation.
Reducing Water Use in Commercial, Public, and Residential Landscapes. Our involvement in research and education measuring evapotranspiration (ET) rates and determining the minimum irrigation requirements of landscape species spans over 30 years. Early work included the design and implementation of the California Irrigation Management Information System (CIMIS) weather station network and determining crop coefficients for warm and cool season turfgrass based on historical ET and CIMIS data.
Our work identifies the minimum irrigation requirements of established landscape trees, shrubs, and groundcovers in diverse climate zones throughout the state, supporting urban water conservation. Through a partnership with the California Department of Water Resources, we developed the Water Use Classification of Landscape Species (WUCOLS) system in the early 1990s which, to date, has classified more than 3,500 landscape plant species into very low, low, moderate, and high water-use categories based on observation and personal experience by UC and industry experts. WUCOLS continues to be updated as we obtain more data from replicated trials. Our work in precision irrigation using smart controllers, remote sensing, and geospatial analysis under controlled conditions improves irrigation efficiency. Irrigation training and certification for public and private landscape managers also remains a priority because, even with advanced smart controller technologies, water savings cannot occur with poorly designed and malfunctioning irrigation systems.
We also develop and extend critical information leading to the formation of statewide water budgets and policy for commercial and residential users through participation on legislator-appointed boards and committees. Our work reduces the obstacles that were inhibiting widespread landscape water conservation including: a lack of credible information regarding landscape water requirements, inadequate training across a large segment of the landscape industry, lagging irrigation system technology, and an inadequate supply of locally available drought-resistant landscape plants.
Reducing Overuse of Pesticides and Fertilizers in Commercial, Public, and Residential Landscapes. Urban landscapes are now the single greatest source of non-point pesticide pollution of California waterways. Home use of pesticides is unregulated, and residential users are often unaware of proper application practices leading to runoff polluted with fertilizers and pesticides. Inefficient irrigation practices by residents and professional landscape managers contribute significantly to runoff leading to waterway pollution. Applied research and education that we develop and extend through the Green Gardener and other educational programs directed at the commercial sector and through the ANR Master Gardener Program (MGP) to non-commercial gardeners reduces reliance on pesticides and fertilizers in urban environments, further reducing water pollution.
Preventing and Controlling Pests and Diseases in Commercial Nurseries/ Greenhouses/ Controlled Environments and Landscapes. Global trade and illegal imports of plants from unlicensed facilities have introduced devastating pests and diseases that irreversibly impact production, end-user sectors of the green industry, and California's natural landscapes, often requiring expensive, area-wide control programs. As global trade and movement of pests into California continue to increase populations of exotic pests and diseases, the need for applied research in detecting and managing them in production nurseries and landscapes has also increased. We help protect California's green infrastructure from the threat of pests and diseases by developing, updating, and implementing science-based best management practices that contain and control them.
We regularly train arborists, growers, land managers, and other green industry personnel to identify and manage a wide variety of pests and diseases, including new invasive species. We also provide education to ANR MGP volunteers and the general public on ways to reduce the spread of invasive species and, in some cases, we involve citizen scientists in our work detecting invasive tree pests.
Addressing Water Quality and Quantity Issues in Nurseries/Greenhouses/Controlled Environments. Federal, state, and local governments mandate elimination and/or reduction of wastewater discharges that exceed established water quality criteria. The passage of the Sustainable Groundwater Management Act in 2014 to protect groundwater resources brought us and ANR colleagues in related disciplines to the forefront working with regulatory agencies and industries to develop long-term groundwater sustainability plans and address fertilizer management to mitigate groundwater pollution.
In addition, due to water scarcity and imposed restrictions due to drought, we develop and extend research-based information to enable water conservation while supplying adequate amounts of water to produce high-quality, functional plants. We also develop technologies and systems to improve the quality and delivery of recycled water which reduces reliance on potable water but can impair irrigation water quality, leading to plugging of nozzles, high substrate salt levels, and plant damage. Our expertise helps nursery and floriculture producers obtain and retain sustainable alternative water sources that minimize dependence on potable water without diminishing long-term economic viability.
Enhancing Human Health and Well-being/Quality of Life. Our work improves the health and quality of life of all Californians benefiting from products and services provided by the green industry. Numerous studies document the myriad ways that landscapes enhance our physical, psychological, sociological, and emotional well-being. Besides providing sources of exercise and recreational opportunities (parks, schoolyards, sports fields, etc.), research affirms that gardening and exposure to nature enhances work productivity, mood, creativity, social bonding, cognition, mental acuity, and a sense of belonging. Studies have also shown that indoor flowering plants reduce stress and improve concentration, productivity, and happiness. In addition, many people engaged in horticulture therapy activities with trained professionals recover more quickly and fully from physical injuries with improved mental health. It is now widely recognized that separation from peaceful, landscaped environments causes stress, increased crime rates, decreased life-spans, and increased incidence of chronic disease in densely populated and sparsely vegetated urban areas, even when controlled for education, race, and income.
Providing ANR MGP Oversight/Research and Extension. We provide vital program oversight and research-based information to over 6,000 ANR MGP volunteers who, in turn, use this information to teach the public how to landscape more sustainably and grow food. Our work provides the foundation to ensure that accurate information is conveyed to the public, ultimately helping protect California's natural resources, reducing overuse and misuse of pesticides, supporting locally grown food, and enhancing health and the quality of life for all Californians.
ANR MGP volunteers are a trusted source of objective research-based information by the gardening public, recording over 395,000 volunteer and continuing education hours in 2019/2020. Surveys completed by Californians after participating in ANR MGP volunteer-led events and classes during this same period document the impact of the program: 74% monitor for insects, weeds, and diseases, which reduces the use of pesticides and waterway pollution; 73% use improved practices to grow food, which reduces food deserts and improves health; 69% spend more time outdoors, which enhances individual and community health; and 67% make use of more plants that attract and support pollinators, which enhances biodiversity and a healthy ecosystem. Our role in providing oversight and research-based information through the MGP will become even more vital due to increased interest in landscaping and gardening by the public. More than four in ten U.S. households (42%) report participating in food gardening in 2020, significantly higher than in 2019 (33%). Importantly, participation by lower income populations, people of color and younger people has outpaced many other demographics.
Developing a Qualified “Green Collar” Workforce for California. Our outreach is critical to familiarize and train interested Californians for green industry careers (arboriculture, landscape pest management, urban water management, nursery, floriculture, controlled environments, etc.) at all educational levels, from those entering the skilled trade to mid-level managers and seasoned professionals and educators seeking to advance their careers and stay abreast of scientific developments. We are front-line teachers for many adult education programs focused on green industry training, often through trade groups and professional associations. Because we are familiar with the local workforce and issues pertinent to clientele in counties we serve, we play a particularly vital role educating the green industry. Often, we are the only source of research-based information locally for early-career individuals with limited resources unable to attend conferences miles away. In addition, we often provide subject-matter material in Spanish through the Green Gardener and other valued programs. As noted below, not only is professional development critical to the individual workers, but a knowledgeable workforce is essential for the proper care and maintenance of California's urban green infrastructure.
Size and Scope of California's Environmental Horticulture Industries
Nursery & Floriculture. The California nursery and floriculture industries have a farm gate value of $3.73 billion (annual average from 2013-2017) and $3.74 billion in 2019, the largest in the United States, accounting for over 20% of U.S. production from 2,609 operations. In fact, only dairy and milk, almonds, and grapes have higher farm gate economic values in California. In addition, California producers accounted for 14% of national bedding and garden plant sales, 34% of potted flowering plant sales, and 78% of total wholesale cut flowers. In 2017, San Diego County ($1.19 billion) dominated California with 43.3% of the state's nursery and floriculture production. (San Diego County and 8 other counties each realized over $100 million and produced $2.25 billion of production). Stanislaus, Monterey, Ventura, Santa Barbara, and Riverside combined were the next largest producers, accounting for 38.7% of total nursery and floriculture production in California. Nursery and floricultural crops ranked in the top 10 agricultural commodities in 36 of California's 58 counties that reported agricultural production.
Landscape Horticulture. The value of the landscape industry in California has been steadily rising as well, totaling over $11 billion of products and related services in 2017. There are more arborists in California (9,560) than any other U.S. state and this number is expected to grow by 11.6% (1,300 jobs) between by 2028. Unfortunately, this increase coincides in many cases with the prevalence of poorly trained, non-certified tree care workers unaware of best practices necessary for ensuring the health and longevity of our urban trees. Less than 10% of individuals in California providing tree care service are certified through the International Society of Arboriculture, a professional development process that increases the competency of an individual's abilities to provide proper tree selection and care and ensures ethical practices.
Aldridge, J. & Sempik, J. (2002) Social and therapeutic horticulture: Evidence and messages from research. CCFR Evidence, 6, 1-4. Anderson G.B. & Bell M.L. Heat waves in the United States: mortality risk during heat waves and effect modification by heat wave characteristics in 43 US communities. Environ Health Perspect. 2011;119(2):210.
Berman, M.G., Jonides, J. & Kaplan, S. (2008) The cognitive benefits of interacting with nature. Psychological Science, 19, 1207-1212. Blair, D. (2009) The child in the garden: An evaluative review of the benefits of school gardening. Journal of Environmental Education, 40(2), 15-38.
Burger, D. (2000) The State of Environmental Horticulture in California: a White Paper for UC-DANR, (Growing Points: Vol. 4, Number 4, Fall). Retrieved from: http://groups.ucanr.org/ehric/documents/Growing_Points4795.pdf.
Butterfield, B. (2009) The impact of home and community gardening in America. National Gardening Association. Retrieved from: http://www.gardenresearch.com/home?q=show&id=3126.
Carmen, H. (2020) Chapter 12: California nursery and floral industry. Giannini Foundation of Agricultural Economics. 2020. Retrieved from: https://s.giannini.ucop.edu/uploads/pub/2021/01/21/chapter_12_nurseryfloral_2020.pdf CDFA)
California Agricultural Statistics Review (2019-2020). California Department of Food and Agriculture. Retrieved from: https://www.cdfa.ca.gov/Statistics/PDFs/2020_Ag_Stats_Review.pdf.
Chen Y. (2017) The impact of biophilic design on health and wellbeing of residents through raising environmental awareness and nature connectedness. University of Georgia Masters Thesis. Retrieved from: chen_yingting_201708_mla.pdf (uga.edu)
Gable, M. & Womack, M. (2020) UC ANR Master Gardener Program Annual Impact Report for 2019/2020. Retrieved from: https://bit.ly/3j6oisl
Gerrish E. & Watkins, S.L. The relationship between urban forests and income: A meta-analysis. Landsc Urban Plan. 2018;170:293–308. pmid:29249844
Hartig T., Van-den-Berg A., Hagerhall C. et al. (2011) Health benefits and nature experiences: psychological, social and cultural processes. In: Forests, trees and human health. Dordrechtr: Springer; 2011. p. 127–168
Hartin, J., Fujino, D., Reid, K., Ingels, C., Haver, D., & Baker, W. (2019) UC ANR research and education influences landscape water conservation and public policy. California Agriculture. 73:1, 25-32. Retrieved from: https://doi.org/10.3733/ca.2018a0041
Hartin, J.S., Fujino, D.W., Oki, L.R., Reid, S.K., & Ingels, C.E. (2018) Water requirements of landscape plants studies conducted by the University of California researchers. HortTechnology. 28:4, 422-426. August. Retrieved from: https://journals.ashs.org/horttech/view/journals/horttech/28/4/article-p422.xml
Jesdale B.M., Morello-Frosch R. & Cushing L. The racial/ethnic distribution of heat risk–related land cover in relation to residential segregation. Environmental health perspectives. 2013;121(7):811–7.
Jenerette G.D., Harlan S.L., Buyantuev A., Stefanov W.L., Declet-Barreto J., Ruddell B.L., et al. Micro-scale urban surface temperatures are related to land-cover features and residential heat related health impacts in Phoenix, AZ USA. Landsc Ecol. 2016;31(4):745–60.
Kroeger T., McDonald R.I., Boucher T., Zhang .P, & Wang L. Where the people are: Current trends and future potential targeted investments in urban trees for PM10 and temperature mitigation in 27 U.S. cities. Landsc Urban Plan. 2018;177:227–40.
Kuo, Ming. (July, 2021). Trees are Essential- Growing Human Health and Equity. California Urban Forests Council. Retrieved from: https://caufc.org/trees-are-essential-growing-human-health-equity/ Landry S.M. & Chakraborty J. Street trees and equity: evaluating the spatial distribution of an urban amenity. Environment and Planning a. 2009;41(11):2651–70.
Masashi Soga, Masashi, K. Gaston & Yamaura, Y. (2017) Gardening is beneficial for health: A meta-analysis. Preventive Medicine Reports, vol.5, pp: 92-99, ISSN 2211-3355. Retrieved from:https://doi.org/10.1016/j.pmedr.2016.11.007
McBride, Joe & Lacan, Igor (2018) The impact of climate-change induced temperature increases on the suitability of street tree species in California (USA) cities. Urban Forestry & Urban Greening. 34, 348-356. Retrieved from: https://www.sciencedirect.com/science/article/pii/S1618866718300013
McDonald R.I., Biswas T., Sachar C., Housman I., Boucher T.M., Balk D., et al. (2021) The tree cover and temperature disparity in US urbanized areas: Quantifying the association with income across 5,723 communities. PLoS ONE 16(4): e0249715. Retrieved from: https://doi.org/10.1371/journal.pone.0249715
McDonald R.I., Kroeger T., Zhang P., & Hamel P. The Value of US Urban Tree Cover for Reducing Heat-Related Health Impacts and Electricity Consumption. Ecosystems. 2020;23:137–50.
Newman, Julie P., Kabashima, John N., Merhaut, Donald, Haver, Darren L., Gan, Jay, Oki, Lorence R. (2014) Controlling Runoff and Recycling Water, Nutrients, and Waste. Container Nursery Production and Business Management Manual, ANR Manual 3540: 95-118.
Reid, K., Fujino, D., Oki, L., Hartin, J., et al. (2018) Maintaining urban landscape health and services on reduced irrigation: A multi-site study in best management practices. ActaHortic.2018. 1215. Retrieved from: https:/doi.org/10.17660/ActaHortic.2018.1215.33
Reid, K. & Gable, M. (2020) University-trained volunteers use demonstration gardens as tools for effective and transformative community education. Acta Hortic. ISHS. 1298, 85-90. December. Retrieved from: https://doi.org/10.17660/ActaHortic.2020.1298.13
Riley C.B. & Gardiner M.M., Examining the distributional equity of urban tree canopy cover and ecosystem services across United States cities. PLoS ONE. 2020;15(2):e0228499.
State of California. (2021) Economic Development Department/LMID Projections of Employment by Occupation. Retrieved from: https://www.labormarketinfo.edd.ca.gov/OccGuides/Detail.aspx?Soccode=373013&Geography=0604000059
Troy, A., Grove, J.M. & O'Neil-Dunne, J. (2012) The relationship between tree canopy and crime rates across an urban-rural gradient in the greater Baltimore region. Landscape and Urban Planning, 106 (3) 262-270.
Twohig-Bennett C. & Jones A. The health benefits of the great outdoors: A systematic review and meta-analysis of greenspace exposure and health outcomes. Environ Res. 2018;166:628–37. USDA California Agricultural Statistics (2017) Retrieved from: https://www.nass.usda.gov/Publications/AgCensus/2017/Full_Report/Census_by_State/California/index.php
Weinberger, Kate R., Harris, Daniel, Spangler, Keith R., Zanobetti, Antonellae & Wellenius, Gregory A. (2020) Estimating the number of excess deaths attributable to heat in 297 United States counties, Environmental Epidemiology: June 2020; 4(3) Retrieved from: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020EF001480
Weston, D.P., Holmes, R.W., You, J., & and. Lydy, M.J. (2005) Aquatic toxicity due to residential use of pyrethroid insecticides. Environmental Science & Technology, 39(24): 9778-9784. Retrieved from http://dx.doi.org/10.1021/es0506354