- Author: Janet Hartin
1. Select drought-resistant plants that grow well in your climate zone and microclimate (sun, shade, etc.). Try these search engines:
SelecTree: A Tree Selection Guide (calpoly.edu) Plant Search Database
Plant Search Database - Water Use Classification of Landscape Species (WUCOLS IV) (ucanr.edu)
For inland San Bernardino County: Home - Inland Valley Garden Planner
2. ‘Hydrozone': Place plants with similar water needs (very low, low, medium, high) together and water the hydrozones on different valves (or, if hand watering, water plants requiring the most water longer but not necessarily more often than other plants).
3. Make sure your irrigation system is operating properly (pressure, spacing, no weeds around heads, no broken parts, etc.).
4. Irrigate based on species and seasonal water needs (highest in summer) and soil type (sandy loam, clay loam, etc.).
5. Irrigate slightly below the current root zone depth of your plants to encourage deep rooting into cooler soil: - 6”-8” for annuals, perennials, and turf - 8”- 1' for shrubs - 1' or deeper for trees
6. Water early in the morning when soil evaporation is minimal.
7. Control weeds. They compete with your garden plants for water.
8. Spread and maintain 2-4” of mulch around garden plants and trees (3-4” for wood chips, 2” for pebbles, decomposed gravel, etc.) keeping it a few inches away from tree trunks.
9. Avoid over-fertilizing. Too much nitrogen creates weak growth and the need for more water.
10. If you have a lawn and still want to keep it, water based on the UC ANR 'Lawn Watering Guide': http://ucanr.org/freepubs/docs/8044.pdf
Contact a trained University of California Cooperative Extension (UCCE) Master Gardener in San Bernardino County for more help! mgsanbern@ucanr.edu (fastest!) or: (909)387-2182 (leave a message for a return phone call)
Redlands trees
- 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.
Bibliography
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
As we enter another summer of drought, conserving water is essential. Luckily, there are a number of ways you can significantly reduce water use in your vegetable garden.
Mulch, mulch, mulch! Mulching is probably the single most important thing a gardener can do to reduce water consumption in a vegetable garden, or the home landscape in general. Mulching reduces evaporation from the soil by up to 35% and can significantly cut irrigation needs. Mulches also smother weeds, which compete with vegetables for water.
Mulching with black plastic sheeting is the most effective way to conserve soil moisture, but it also raises soil temperatures, so its use should be limited to heat-loving vegetables such as tomatoes, peppers, eggplants, cucumbers, squash and melons. Plan to lay down black plastic early in the season, so that by the time extreme summer temperatures arrive, plants will have matured and their leaves will shade the plastic.
Grass clippings make excellent mulch because they release nitrogen into the soil as they break down. To avoid matting, clippings should applied in thin layers between one-quarter and one-half an inch deep and be allowed to dry out between layers. Do not use grass clippings from lawns that have been treated with herbicides. Other organic mulches include wood shavings, compost, bark, straw, or alfalfa. Organic mulches should be one to three inches thick in vegetable gardens; the larger the mulch particles, the thicker the mulch needs to be. Also, thicker layers of shavings, straw, or bark may lead to a carbon-nitrogen imbalance in the soil. A layer of newspaper two sheets thick can be placed under organic mulches to enhance their effectiveness. (Do not use glossy printed material for this purpose, as the ink may be toxic to plants.)
When deciding which vegetables to plant, be aware that the amount of water needed by different crops varies. Corn and most beans require the greatest water use of commonly-planted garden vegetables. Vegetables that are more drought tolerant include chard, black-eyed peas (cowpeas), heat-tolerant tomatoes (including many cherry varieties), some varieties of okra, mustard greens, eggplant, jalapeno and poblano peppers, Black Knight zucchini, and New Zealand and Malabar spinach. Shallow-rooted crops, including potatoes, onions (and most other bulb, root or tuber crops), celery, and plants in the cabbage family, require more frequent irrigation. For this reason, mulch is especially beneficial for shallow-rooted crops. Tomatoes, sweet potatoes, melons and asparagus are more deep-rooted and can tolerate longer periods without irrigation. Beans, carrots, peppers, summer squash and cucumbers are intermediate in root depth. Additionally, low-growing plants and plants with smaller leaves tend to lose less water through their leaves than taller, leafier varieties. Bush beans, for example, use less water than pole beans. Also, miniature varieties of vegetables, such as mini bell peppers and eggplants, need less water for fruit development than standard varieties.
How a garden is irrigated can affect how much water it uses. Water early in the morning, so that water has a better chance to soak into the soil before it evaporates. A drip system (under mulch) is an efficient way to deliver water to crops with minimal evaporation loss. To avoid overwatering, monitor soil moisture. Generally, if garden soil has dried out to a depth of two to four inches, it's time to water. Including a timer as part of an irrigation system will reduce waste due to human error. Overhead sprinklers and hose-end sprayers are inefficient, result in high evaporation losses and are more likely to trigger diseases such as mildew. Also, the amount of water needed by plants varies over their life cycle. As a rule of thumb, water is most critical for plants during the first few weeks of development, immediately following transplanting, and during flowering and fruit production. Target the timing and amount of water with these plant needs in mind. It is also important to check and maintain your irrigation system frequently to keep it performing at top efficiency.
For more information, see “Water Conservation Suggestions for Your Home Vegetable Garden." UCCE Master Gardeners of Trinity County.
The Master Gardeners Spring 2021 Workshop Series is underway. It is not too late to sign up for our workshop on Honeybees, and an upcoming 4-part series on Firewise Landscaping. Check our website to read about these free workshops and register for them.
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu (preferred) or call (530) 538-7201.
- Author: Janet Hartin
I hope all of you and your loved ones are staying well and healthy as the pandemic continues. Involving yourself in outdoor activities is not only a great way to escape 'cabin fever' and improve your physical health but it is also good for you psychologically, as well.
A silver lining for me over the past few months has been the opportunity to summarize results of some research studies including an update from a mulch trial that I'll report on virtually rather than live at the American Society for Horticultural Science conference (that was to be held in Orlando). I thought you might be interested in the results.
The objective of the research project was to measure the impacts of organic mulch treatments on the growth and health of four species of low maintenance, drought-tolerant landscape trees under deficit irrigation. Species selected were Parkinsonia x ‘Desert Museum' (it's thornless!); Chilopsis linearis ‘Bubba' (Desert Willow) (beautiful magenta flowers!), Pistacia ‘Red Push' (hybrid from P. atlantica and P. integerrima with brilliant orange fall foliage), and Prosopis glandulosa ‘Maverick' (thornless). Trees were planted in a randomized complete block experimental design in at the Chino Basin Water Conservation District (CBWCD) in Montclair in October, 2016. Half of the trees received 4” of organic mulch and half did not. Trees were transplanted from 15-gallon containers and irrigated with recycled water at 80 percent of reference evapotranspiration (ETo) the first 12 months.
Irrigation was reduced to 50% ETo in November, 2017 which was maintained until May 2020, when irrigation ceased. While the study continues through October 2020, there are some interesting early results. Organic mulch applications enhanced growth with no loss in quality in the Pistacia, Prosopis glandulosa, and Chilopsis linearis trees while growth was actually better in the Parkinsonia trees that did not receive mulch. This may be due to the fact that its trunk and branches actively photosynthesize as well as its leaves. Parkinsonia leaves also feature sunken guard cells, providing another form of drought avoidance. Furthermore, they develop deep root systems and may not need the added benefit of reduced soil evaporation in the top few inches of soil provided by the mulch. While all of the species selected have wonderful attributes, the Parkinsonia 'Desert Museum' has all the best traits of its palo verde heritage including having no thorns and a continues bloom throughout summer.
A huge thanks to our UCCE San Bernardino County Master Gardener team (led by Irene) who take data quarterly on the trees, recording trunk circumference at 6" and 3'. This is another great example of the breadth and depth of the contributions of our wonderful volunteers!
The four species of landscape trees in this study are part of a larger study at University of California, Riverside to determine the ability of 12 species of landscape trees to mitigate impacts of climate change. While I'll be long retired, growth and health data of all species will continue to be evaluated through at least 2035. The study at CBWCD provided the opportunity for a mulch/no mulch treatment for four of the most promising species which was space-limited at UCR.
Below are plot photos from October 2016 (right after planting), July 2020 (no irrigation for 3 months), a mature 'Desert Museum' tree in prolific bloom (photo credit to Dr. Bob Perry, Emeritus Professor, Cal Poly Pomona), and a mature Chilopsis linearis 'Bubba' from our UCR plot.
Save the date! We will be hosting a virtual UCR Field Day on September 3, 2020 featuring our drought-tolerant landscape plots at UC Riverside that was to be held live last May. More information is forthcoming but it will provide at least four hours of continuing education hours and a chance for you to ask questions of Dr's Amir Haghverdi, Don Merhaut and myself.
Have a wonderful August in your garden!
Janet
- Author: Steve I Morse
Advice for the Home Gardener
from the UC Master Gardener Program
of Contra Costa County
Client's Request: Hello. We would like to plant a shade tree in our backyard in mid-County. We have a fairly shallow well… and am assuming a high water table although we don't have any wet, boggy areas. We have two semi-dwarf orange trees s that we never water and they are productive and sweet. Can you recommend links for some shade trees in these conditions .... such as Crape Myrtle, deciduous Magnolia, and Japanese Maples? Thank You.
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with a question about tree selection. You didn't say how deep your well is, but the water table is probably deep enough that it won't impact trees in your landscape. Tree roots are generally found in the top 1 to 3 feet of soil, with only some sinker roots possibly venturing deeper. Trees don't usually have tap roots past the seedling stage, but rather grow roots that extend well past the dripline (outer edge of the tree's canopy).
If you have good drainage in your soil, any tree suited for your climate should be fine. To test your drainage, dig a hole about a foot deep. Fill it with water and allow it to drain completely. Immediately refill the hole and measure the depth of the water with a ruler. Fifteen minutes later, measure the drop in water in inches, and multiply by 4 to calculate how much water drains in an hour. Ideally, you should have 1 to 6 inches drainage per hour.
The trees you specifically asked about were Crape Myrtle, deciduous Magnolia and Japanese maple. Crape Myrtles (Lagerstroemia spp.) do well in mid-county. They need full sun and seem to appreciate our hot summers. There are many varieties to choose from. This link is to an article from the Sonoma County Master Gardeners about growing Crape Myrtles: http://sonomamg.ucanr.edu/Plant_of_the_Month/Lagerstroemia_spp_Crepe_Myrtle/.
Deciduous Magnolia may not be a good choice. According to Sunset Western Garden Book, deciduous magnolias with saucer flowers do poorly in hot and dry areas. Deciduous magnolias with star flowers seem to do better, but are very slow-growing, and the variety called Star Magnolia (Magnolia stellata) stays quite small and is usually grown as a shrub.
Japanese maples (Acer palmatum) do best in cool climates and will need partial shade and protection from hot, dry wind in the hotter areas of the County. Morning sun and afternoon shade is best. The varieties with green leaves do better with more sun exposure than the varieties with red leaves or those with lacier leaves.
You might also consider Chinese pistache (Pistacia chinesis). It is well suited for our climate and makes a good shade tree. This link is to another article from the Sonoma Master gardeners: http://sonomamg.ucanr.edu/Plant_of_the_Month/Chinese_Pistache/.
For other ideas, this link is to a searchable database where you can select aspects you want such as shade tree, deciduous, maximum height, etc. https://selectree.calpoly.edu/about. They have good descriptions of the trees, along with photographs.
If after you perform a drainage test you find you have poor drainage (less than 1 inch per hour), contact us again and we will research those trees more suitable for a boggier area. Don't hesitate to contact us if you have any questions.
I hope this information is helpful and you find a good shade tree for your yard!
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.edu/HortCoCo/ You can also subscribe to the Biog.