- 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.
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- Author: Janet Hartin
Did you know that many landscape problems are not caused by either diseases or insects? In the majority of cases the culprits are poorly drained soils, irrigation issues, trees in too tight of quarters or improperly pruned, and other non-living (abiotic) maladies. The good news is that most of these issues can be prevented. Follow these suggestions to steer clear of common abiotic problems in your landscape. Following these suggestions will also help your plants stay healthy and better able to fend off insects and diseases they would otherwise be vulnerable to.
Select plants that grow well in your climate zone. Choosing the right plant for the right place is a sure way to green up your thumb and keep your plants healthy and attractive. The Sunset climate zone map is a great resource for finding out what climate zone you are in. These zones are more accurate for most areas of California than USDA plant hardiness zones since they are smaller and take into account more relevant factors than do the USDA hardiness zones. An exception are mountain communities in which case either resource works equally well. Click here to find your Sunset climate zone https://www.sunsetwesterngardencollection.com/climate-zones and here to locate your USDA plant hardiness zone: https://planthardiness.ars.usda.gov/PHZMWeb/.
Select plants that will grow well under various ‘microclimates' around your home. Microclimates are smaller areas within your larger climate zone that further determine the suitability of a plant for a specific spot. Typical microclimates are sunny or shady areas, sections of your yard that get splashed by chlorinated water from a pool or spa, narrow strips in side yards that are too small for a large-growing tree, and poorly drained soil with not enough air to support plant growth. While all plants need adequate space, trees need the most. While a beautiful shade tree like a ornamental fig, magnolia, or rosewood might be tempting, they all need about 3,000 cubic feet of space underground and 50 feet or more above ground clearance at maturity. Otherwise roots can buckle sidewalks and driveways and branches can interfere with utility lines. There are many smaller-maturing trees such as acacia, mesquite, crape myrtle, and dozens of other species that won't cause these problems and are good choices for smaller areas.
Be sure to do adequate research on the expected size of a tree you're interested in before making a purchase. Care tags, UC Cooperative Extension Master Gardeners, and nursery and garden center personnel are all good sources of help to match a plant's requirements regarding space, sun, and shade and their tolerance to salt spray, problem soils and other restrictions with conditions in your own yard. Three excellent searchable plant databases for finding suitable plants for your climate zone and microclimate conditions are: Urban Forest Ecosystems Institutes (https://selectree.calpoly.edu/); California Native Plant Society (https://calflora.org/); and UC's California Center for Urban Horticulture Water Use Classification of Landscape Species (WUCOLS) (https://ccuh.ucdavis.edu/wucols-iv).
Apply the right amount of water at the right time. Many newly transplanted landscape trees, shrubs, and flowers die from the soil drying out too much between waterings. Their root systems are small and need to be kept moist for the first few weeks in their new home (or a full season for a tree). This holds true for drought-tolerant species as well as those that require more water. Once plants become well-rooted they should be watered less often but for longer periods of time. Water slightly below their current root system to encourage downward growth. This practice is especially important for trees since it promotes deeper roots better able to support and stabilize above-ground growth.
Since tree roots spread outward as well as downward, water should be applied beyond the dripline of the tree as well. Some soils never fully drain leading to low oxygen levels than hamper tree growth and can eventually kill the plant. To test for adequate drainage before planting a tree, dig a hole at least one foot deep and one foot wide and fill it with water. If it doesn't drain in one day or less a tree should not be planted at that site.
Hydrozone (place plants with similar water needs together). If your landscape is irrigated on an automated system, you can save water and reduce your water bill by grouping plants according to their water need. Divide your landscape into very low, low and medium water use hydrozones at the design stage and remember to replace any dead plants with new ones requiring a similar amount of water. This allows you to fine tune how often and how long to water each zone. Hydrozoning also helps you stay within a medium or even low water tier even if you have designated high water use areas for vegetables and fruits that generally require higher amounts of water than most landscape plants.
Prevent soil compaction and poor drainage. Avoid adding soil amendments to tree planting holes. Trees need adequate underground support as they grow upward and become heavier. Trees in either too small of planting hole or in holes where compost or other organic soil amendments have been added may grow in circles around the hole, never venturing outward beyond the constraints of the hole. Trees may eventually topple, causing injury to people and nearby structures. Instead, dig a hole at least twice the width of the container and at the same depth the tree you will be transplanting came in, remove the soil, gently plant the tree, tamping the original soil around the plant. Remember to water the newly planted tree in well and keep the rootzone moist the first season as discussed above.
Add soil amendments (including compost) to soil before planting small ornamental plants and edibles. They add valuable organic matter to the soil, improving aeration and drainage in heavy clay soils and water-holding capacity in sandier soils. Compost also adds valuable microbes that break down the organic matter improving overall soil health. Mix enough soil amendments into the soil so that the final volume contains about 40% soil amendments and 60% original soil. Make sure that the soil amendment is mixed into the soil evenly and completely. Do not add soil amendments to tree-planting holes to avoid circling roots.
Correct high pH (alkaline) soils. Southern California soils tend to be alkaline, with average pH ranges from 7.1 – 7.6. (Most plants prefer a neutral pH of 7.) Highly alkaline soils often tie up nutrients necessary for plant growth - such as iron, zinc, and manganese – making them unavailable to the plant. Once the pH is reduced, the problem is often resolved.
Avoid salt damage. Damage due to too much fertilizer or water high in certain salts (such as chlorinated swimming pool water) can cause brown leaf margins and leaves that look scorched. Over time, the damage gets worse and sensitive plants may die. One way to reduce the chance of too many salts building up in your soil is to not over-fertilize. For instance, woody trees and shrubs do not need to be fertilized at planting time and older trees may get all the nutrients they need from fertilizer applied to neighboring lawns and plants. .If symptoms of nitrogen deficiency (yellow newer leaves) do appear, apply no more than .25 lb/actual nitrogen per inch of trunk circumference. Leaching salts out of saline soils (applying water over what may be a few hours very slowly so it can drain salt build-up below the roots) may be necessary to avoid damage to your plants.
Take Care of Your Trees. Trees are likely the most highly valued plants in your landscape. They provide shade, reduce temperatures in hot urban heat islands, add beauty, and even help clean the environment by storing carbon dioxide. Prune trees correctly.
Don't top trees! Topping a tree is the process of giving a tree a virtual crewcut by making one or more horizontal cuts across the top of the tree (add photo) to shorten it. Why is topping trees harmful? Topping trees results in unstable, unsafe, and unattractive trees. It also reduces the ability for trees to reduce high temperatures and provide adequate shade in urban heat islands, sequester (store) carbon produced by fossil fuels, and provide wildlife habitat. In some cases, trees are topped because a tall tree that should not have been selected in the first place is growing into utility lines. In other cases, topping occurs due to a lack of knowledge about the dangers of topping and/or simply wanting to save money by going with the lowest bid. In all cases, topping should be avoided. The combination of improper balance and weak, poor-quality growth following topping creates a much higher likelihood of personal injury and property damage than occurs from properly pruned trees.
Trees should be properly thinned and pruned rather than topped. Proper pruning involves maintaining the natural integrity and balance of the tree. (For detailed information on proper pruning visit the International Society of Arboriculture's (ISA) consumer website: www.treesaregood.org). Contact a Certified Arborist (https://www.isa-arbor.com/Credentials.) who is trained in tree health and care if you are in doubt about caring for your landscape trees. S/he will determine the proper pruning and thinning procedures and otherwise assess the overall health of your tree.
Prevent Circled and Kinked Tree Roots. Circled, kinked tree roots can lead to stressed trees that drop limbs or topple, causing injury to people and structures. They occur when trees are left too long in containers, are planted in too small of a planting hole, or when the planting hole is filled with organic matter such as compost. In the latter case, roots will often prefer the higher quality compost to the surrounding native soil and never grow beyond its bounds. In some cases, one or more condition exists. To avoid these problems, make sure roots are not overgrown at the time of purchase and do not add soil amendments to the planting hole.
Avoid Mechanical Injury to Tree Trunks. Remove staking ties before they cut off the flow of water and nutrients in the vascular system of the trunk. If the tree will not support itself due to high winds, loosen the ties and move outward any stakes that may rub the trunk as the tree grows. Add mulch around trees (but avoid contact with trunks) to prevent damage from mowers and weed trimmers. (Mulch also reduces soil evaporation and weed seed germination).
Avoid Soil Grade Changes. Grade changes from construction activities should be kept several yards from trees. Even small changes in the depth of the soil can result in serious root system injury. As little as four to six inches of soil applied on top of the root zone of a mature tree can dramatically reduce the amount of oxygen available to roots and can kill a tree over time. Lowering the grade can cause lower trunk and root injury and reduce the nutrient and moisture supply to the roots.