- 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
By David Walther, UC Master Gardener of Butte County, March 2, 2018.
Mulch is good for the soil, and thus good for your plants for a number of reasons. It jump-starts the useful work done by microscopic organisms (this is often referred to as microbial activity); retains moisture, thus preventing plants' roots from drying out; and deters weeds by providing a barrier between the soil and the sun.
Mulching is also a time-saver for the gardener – it takes a fraction of the time to put down mulch that it would take to weed later on. And using mulch to control weeds reduces the use of expensive herbicides.
Natural inorganic mulches include gravel, pebbles, and crushed stone. Other inorganic mulches are plastic, cardboard, and even pieces of old carpet. The mulch you use will depend upon the job you want the mulch to perform and how you want it to look.
Any ground that needs enrichment, such as flower or vegetable beds you will be planting later in the season, will benefit from an application of organic mulch. Mulching around shrubs, trees, annuals, and perennials will improve the soil that feeds their roots, as well as deter weeds. Large areas that you wish to keep weed-free are also candidates for a thick application of mulch.
To control annual weeds, apply four to six inches of mulch on top of the soil, or even on top of the weeds themselves. To control perennial weeds, an application of 12 to 16 inches of mulch is needed.
The reappearance of weeds in an area that has been mulched is an indication that the mulch has decomposed to such a degree that a new application of mulch is required.
While the benefits of applying mulch are many, mulch can also lead to an increase in mole activity because of the increase in the worms and grubs they feed on – the more alive your soil is, the more it becomes a habitat for other creatures.
Finally, different garden situations require different choices of mulching materials: for example, dryland garden plants (xeriscape plants) such as native California plants, cacti, and succulents, have evolved to flourish in dry conditions and poor soil. The moisture-retentive qualities of organic mulch could be detrimental to their vigor and growth while the use of stone or gravel mulch would be helpful in replicating their natural environment.
Your mulch choices can range from commercial mulches purchased at a landscape center, to bags of organic mulch available at nurseries and home improvement stores, to your own (free!) shredded leaves, grass clippings, and yesterday's paper. The benefits of mulching far outweigh any negatives, so there is no reason not to mulch.
For more information see: Mulches
Questions? Plant problems? Call the Master Gardener Hotline at 530-538-7201 and/or visit our website Hotline page at ucanr.edu/p/49588.