Healing plants with compost tea in the UC Botanical Garden
There are inherent problems in cultivating a botanical garden. Meant to serve as a living museum, a botanical garden brings plants from other ecosystems, countries, and continents together so that a visitor may experience the vegetation of far away places. The University Botanical Garden, spreading out over 34 acres in Strawberry Canyon and serving as a home to rare and endangered species from all over the globe, is no exception. Not all plants in the garden were tailored for the soil of the Berkeley Hills, and certainly not all of them grew prepared for the myriad of pathogens that the diverse California ecosystem brings.
Regardless, the collection is as beautiful as it is extensive, and it must be maintained. Two of the keys to proper garden maintenance are nutrient input and pest management – and the UC Botanical Garden is currently taking steps towards less traditional, more “eco-friendly” solutions to these processes.
Until 2010, the UC Botanical Garden maintained its collection largely through the use of modern fertilizers and pesticides alongside traditional gardening techniques. In 2010, the UC Botanical Garden tapped into Cal’s “The Green Initiative Fund” (TGIF) in order to being the process of what they called “Greening the Garden”, which initiated an integrated pest management program centered on the use of compost tea.
Coming from an ecological standpoint, Anthony Garza, the supervisor of Horticulture and Grounds at the Garden, explained the reasoning behind greening the garden: “we were not at a chemical burnout, but wanted to stop using pesticides, particularly fungicides, outdoors in order to protect staff, the public, and the environment.” With Strawberry Creek collecting in a pool before running through the rest of the garden, down to campus, and out to the bay, there was concern that the chemicals used in the garden could quickly escape the control of the horticuluralists there and cause damage in unpredictable ways downstream.
To replace these potentially harmful chemicals, the garden staff turned to compost tea as a more natural solution to pest issues.
Compost tea is a water extract of healthy, thermophillic – or warm – compost, where the “warmth” comes from the metabolism of organisms breaking down the dead plant material present. Dr. Elaine Ingham, a soil biology researcher at Soil Foodweb Inc, found in her work that many of the bacteria, fungi, nematodes, and protozoa present in thermophillic compost provide a variety of beneficial services besides breaking down plant material. These microorganisms are extracted from compost into a large quantity of water and mixed with liquefied fish and kelp, which serve as food so that they can propagate and saturate their brewing tank, creating a probiotic smoothie for plants. When this smoothie is sprayed on vegetation, the microorganisms, which are natural predators of many pathogens, will begin to consume pathogens on a microscopic level as well as physically occupy the locations on plants’ root systems, stems, and vegetation that they may use to enter the plant. In addition, the beneficial microorganisms soak into the soil surrounding a treated plant, where they continue to carry out their metabolic processes and bring fertility to the soil.
The UC Botanical Garden currently employs two student interns, who prepare and apply compost tea in 100 gallon batches for disease prevention and containment in the garden. Batches will occasionally be augmented with the addition of other beneficial microorganisms to target specific diseases, as well as extra liquid fish and kelp in order to provide extra nutrients in target soils. While it is certain that there are fewer EPA-regulated chemicals being washed down Strawberry Creek, the beneficial effects of compost tea are uncertain. To date, there has not been an empirical study on the actual effect compost tea has had in the garden, but anecdotal evidence from several staff members points to a positive result, supported by the fact that the garden has only needed to resort to chemical use for small and specific incidents.
Howevwe, that benefit may never be fully measured, as the grant money from the Green Initiative Fund is nearly used up, and the garden has found itself unable to locate the extra funding necessary to keep the project staffed into the future. Moving forward, Garza makes it clear that the garden will not be returning to the practices of years past, stating that “the Botanical Garden takes seriously it’s responsibility to ensure that the intrinsic value of the Strawberry Canyon watershed in which it sits is protected for the sake of its flora and fauna, and for enjoyment and use by UC students, staff, faculty, and visitors.”