Posts Tagged: Master Gardeners
Welcome to another “New Normal!” Due to climate change resulting in hotter, drier conditions and reduced snowpack, the occurrence of a “fire season” which traditionally occurred from May through October is becoming a misnomer, with fire occurring throughout the year. The severity of what may lie ahead over the next several months was highlighted in a recent tweet posted by CAL FIRE: “Compared to last year, California has seen over 2,650 more fires and a nearly 2000% increase in the acres burned year-to-date (January 1 – September 7), across all jurisdictions.”
Indeed, Fall often hosts strong offshore winds that can quickly spread destructive fires, exacerbated by the impacts of climate change. What can you do to help ensure ‘defensible space' that increases the safety of your family, pets and property in fire-prone areas? First and foremost, select and properly maintain fire-resistant plants augmented with hardscapes and fire breaks extending from your home to at least one hundred feet outward. (This also helps ensure access to your home by firefighters and other first-line responders in the event of a fire or other life-threatening event.)
Vegetation chosen for your defensible space should have low flammability and can include trees and shrubs along with herbaceous plants. Allowing adequate space between woody plants is important to avoid a continuous fuel path (fuel ladder) where fire starting at ground level can climb to the top of a tree and spread from tree to tree.
1. Follow these ‘defensible space' guidelines to reduce the risk of fire spread and damage:
Zone 0 (first 5 feet from structures): avoid anything combustible including woody plants, mulch, woodpiles, trellises, and stacked items. Instead, add walkways and mulch and other hardscaping made from pebbles and rocks, pavers, rock mulch, or pea gravel. Include a 6-inch noncombustible area extending from the ground to the exterior siding of structures.
Zone 1 (5-30 feet from structures): Eliminate fire spread by ensuring adequate space between trees, removing lower branches. Consider adding irrigated groundcovers or mowed grass or hardscapes between these plant groupings, as well. Properly maintain plants and remove dead portions of plants.
Zone 2 (31-100+ feet from structure to the property line): Concentrate on reducing the density of plants to slow the spread of fire and to reduce the height of flames. Woody plants should be spaced (as illustrated below) to prevent fuel ladders.
Defensible Zones (source: National Fire Protection Association, nfpa.org)
2. Remember that even a so called “fire-resistant” species that is under-watered or otherwise poorly cared for can be highly combustible. The conditions under which the plant is grown influences its fire-resistance more than the species itself. However, plant species high in wax, oil, and resins such as conifers tend to be highly flammable while manzanita and ceanothus (California lilac) are less so.
3. Avoid planting or spreading invasive species. While invasive plants are never recommended in any landscape, they are especially problematic in natural areas prone to wildfire. Once established they can fuel fire as well as crowd out native vegetation and associated habitat. Refer to the California Invasive Plant Council website for more information and specific examples and plants to avoid (www.cal-ipc.org).
4. Follow recommended planting and pruning guidelines to prevent both horizontal and vertical spread from tree to tree. Horizontal spacing is directly related to the slope of the land and the height of the vegetation.
Photo above (courtesy of CAL FIRE) is a diagram to help you determine minimum horizontal clearance for tree and shrub placement to reduce fire risk.
Photo above (courtesy of CAL FIRE) shows a 5' shrub near a tree. In this example, 15' of clearance (3 x 5') is needed between the top of the shrub and the lowest tree branch to prevent a fire ladder.
5. While fire-resistant natives and adapted non-natives greatly reduce your chance of losing your home and property to wildfire, all plants will burn under favorable conditions. Ensure that plants receive adequate irrigation.
6. Rather than applying organic mulch near your home, use non-flammable materials such as stone and pebbles. Granite pathways are also suggested since they provide a fuel break. Firewood and propane tanks should also be kept away from your home.
CAL FIRE “Ready for Wildfire”: https://www.readyforwildfire.org/prepare-for-wildfire/get-ready/defensible-space/
Drill, S. et al. (2009), S.A.F.E Landscapes: Southern California Guidebook, UC Cooperative Extension: https://ucanr.edu/sites/SAFELandscapes/files/93415.pdf
UC ANR “Preparing Home Landscaping for Fire”: https://ucanr.edu/sites/fire/Prepare/Landscaping/
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!
Doug Arnold is 100% home-grown and has been a UC Cooperative Extension (UCCE) San Bernardino County Master Gardener in the High Desert since 1997. Doug and his wife have lived in the High Desert since 1982. He enjoys DIY projects, such as building raised...
When Loleta first learned she had been chosen for the Monthly Master Gardener Spotlight for March, she said she didn't think there would be much of interest about her to put in the article. I soon came to the realization that this was Loleta's humility...
Sandy Szukalski and I enjoyed a visit to the McKinley Elementary School Garden this past week. Virgina 'Gin' McMillin, the Garden Director had an amazing amount of enthusiasm for the garden, the children, her IERCD grant, the future...