Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County

Client's Request: I am about average in composting: mix a balance of brown and green; no weeds, seeds, meat, dairy products; moist like a squeezed-out sponge; and rotate/turn over. The internal heat will promote digestion – and result in some “steam.”

With my small garden, the beds fill to overflowing. Thus, I do not always apply all my compost. My question: Can compost “go bad?” if it dries out? If it is not used for months? Thank you!

MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your compost question. You asked if compost would go bad if it dries out. The answer is not really, but it can change. If it completely dries, it may become a little difficult to wet the compost. You might want to moisten it before putting it into your garden. 

When compost completely dries, many of the microorganisms (bacterial and fungi) will die, but some will form "survival capsules" or spores that will keep them alive until better conditions come along. Also, good soil is teeming with microorganisms that will "repopulate" the compost, and will continue to break down compost added to the soil. 

So, compost that has dried is fine to use in your garden. It just needs some management. And congratulations on being a successful composter!

Please let us know if you have more questions.

Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)

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Note: The  UC Master Gardeners Program of Contra Costa'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.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/)

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DAVIS--Hear that honey bee buzzing toward a flower? It's not just the nectar that she's scented.

Nectar-living microbes release scents or volatile compounds, too, and can influence a pollinator's foraging preference, according to newly published research led by UC Davis community ecologist Rachel Vannette.

The groundbreaking research, published in the current edition of New Phytologist journal, shows that nectar-inhabiting species of bacteria and fungi “can influence pollinator preference through differential volatile production,” said Vannette, an assistant professor in the UC Davis Department of Entomology and Nematology.

“This extends our understanding of how microbial species can differentially influence plant phenotype and species interactions through a previously overlooked mechanism,” Vannette said. “It's a novel mechanism by which the presence and species composition of the microbiome can influence pollination.”

“Broadly, our results imply that the microbiome can contribute to plant volatile phenotype,” she said. “This has implications for many plant-insect interactions.”

Their paper, titled “Nectar-inhabiting Microorganisms Influence Nectar Volatile Composition and Attractiveness to a Generalist Pollinator,” may explain in part the previous documented extreme variation floral volatiles that Robert Junker of University of Salzburg, Austria, and his team found; New Phytologist published their work in March 2017.

In their study, the Vannette team researchers first examined field flowers for the presence of nectar-inhabiting microbes, and in collaboration with co-authors Caitlin Rering and John Beck of the U.S. Department of Agriculture's Agricultural Research Service (USDA-ARS), Gainesville, Fla, characterized the headspace of four common fungi and bacteria in a nectar analog. Next, they used an intricate setup to quantify the antennal and behavior responses of honey bees to the chemical compounds. Finally, when they examined the scent of flowers in the field, they found that flowers which contained high densities of microorganisms also contained volatile compounds likely produced by those microbes, suggesting that microbial scent production can be detected and used by pollinators.

Although microbes commonly inhabit floral nectar, microbial species differ in volatile profiles, they found. “Honey bees detected most of the microbial volatiles or scents that we tested,” Vannette said, “and they distinguished the solutions of yeasts or bacteria based on volatiles only.” This suggests that pollinators could choose among flowers based on the microbes that inhabit those flowers.

The yeast Metschnikowia reukaufii produced the most distinctive compounds (some shared with the fruity flavors in wine) and was the most attractive of all microbes compared. This yeast is commonly found in flower nectar and is thought to hitch a ride on pollinators to travel from one flower to the next. Its scent production may help it attract pollinators, which then help the yeast disperse among flowers.

The Harry H. Laidlaw Jr. Honey Bee Research Facility, UC Davis, provided the honey bees. More than 20 species of flowers--mostly natives--were used in the survey, including canyon delphinium or canyon larkspur (Delphinium nudicaule), sticky monkey flower (Mimulus aurantiacus), salvia (Lepechinia calycina) and purple Chinese houses (Collinsia heterophylla). The samplings were done in the spring and early summer, when the natives are at their peak.

Co-authors of the paper are Caitlin Rering, postdoctoral fellow at USDA-ARS, Gainesville, Fla.; John Beck researcher at USDA-ARS; Griffin Hall, junior specialist in the Vannette lab; and Mitch McCartney in UC Davis Department of Mechanical and Aerospace Engineering.

The USDA and USDA-ARS funded the research.

Often in our gardening endeavors, it is only the plant itself that we know. However, beneath the soil we cultivate is a vast network of other natural helpers, working hard to ensure the right environment for plants to grow.

While earthworms, burrowing bugs and other critters are familiar sights, among the smallest—but very important—organisms are mycorrhizae.  Put simply, these are fungi that form close relationships with plant roots.  

 

This association allows for nutrient exchange between the plant and the mycorrhizae, benefiting both. These fungal organisms are small—much smaller than the root systems they associate with. In a way, they are extensions of the root systems, and as they penetrate the small pores in the surrounding soil, they extract key nutrients that the plant might not access otherwise.

 

As you might imagine, this relationship is critical for plants in nutrient-poor soils. Mycorrhizae have even been known to help bind toxic residues, such as heavy metals, preventing uptake by the host plant. These fungal partners also increase the surface area of a plant's root system, allowing for better nutrient absorption, structural anchoring and overall resilience. 

 

The full range of benefits that mycorrhizae offer is beyond the scope of this article, but a bit of basic science can help you appreciate why they are important.

 

While some mycorrhizae actually penetrate plant cells and carry out their processes internally, others reside outside the plant cells. Complex chemical cues and interactions attract—or in some cases repel—these fungi and their plant hosts. 

 

Many of these relationships are very specific, requiring a direct match between plant host and fungi. The host provides carbohydrates, and the fungi break down and supply other vital products that the plant can eventually use.

 

Many of us think about fertilizer or soil amendments when we think about plant health.  But the microscopic biological activity of mycorrhizae is critical to the health of our gardens, too. 

 

Consider the mycorrhizae when deciding on treatments for pests or diseases. Toxic chemicals can leach into the soil, adversely affecting beneficial soil microorganisms. Fungicides present special concerns because mycorrhizae are fungi. Do your homework and read any label directions before use.

 

Also think about the impact of soil disturbance. Tilling soil breaks up those extensive root networks, which take time to get established. 

 

Perennials and shrubs aren't the only plants that benefit from these microorganisms. Many trees form extensive networks with mycorrhizae and share nutrients and nitrogen. Fungi help with soil tilth as well. Their fine structures improve water retention and soil aeration, and they help break down soil minerals due to acids they secrete.

 

Given the benefits attributed to these organisms, some gardeners consider inoculating their soil with them. While many commercial growers do so, home gardeners typically have enough microorganisms in their soil to do the job. 

 

However, if you have recently planted a bed with sterile soil media—or are just curious to see if your yields increase—you could inquire at local nurseries about a product for your particular needs. Remember that the goal is healthy soil. Mycorrhizae make a contribution, but so will minimizing the use of harmful chemicals, encouraging earthworms and other native soil inhabitants, and practicing good gardening habits such as crop rotation and mulching.

 

The next time you step into your garden, consider the great events taking place just beneath your feet.  Although the produce we harvest is the most tangible part of our efforts, an entire underground universe of mycorrhizal connections and structures makes it possible.

 

Workshop: U. C. Master Gardeners of Napa County will host a workshop on “Rose Pruning” on Saturday, January 7, from 10 a.m. to noon, at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Certified Rosarian Lynne Andresen and other Master Gardener rose enthusiasts will demonstrate and explain proper pruning techniques and review rose types, common rose disorders and routine maintenance. Online registration (credit card only); Mail-in registration (check only or drop off cash payment).

 

Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.

 

An ambitious effort to sequence the genomes of 100,000 infectious microorganisms and speed diagnosis of foodborne illnesses has been launched by the University of California, Davis, Agilent Technologies, and the U.S. Food and Drug Administration.

Bart Weimer, professor in the UC Davis School of Veterinary Medicine, serves as director of the 100K Genome Project and co-director of the recently established BGI@UC Davis facility, where the sequencing will be done. Other collaborators include the U.S. Centers for Disease Control and Prevention and the U.S. Department of Agriculture.

The new five-year microbial pathogen project focuses on making the food supply safer for consumers. The group will build a free, public database including sequence information for each pathogen's genome — the complete collection of its hereditary information. The database will contain the genomes of important foodborne pathogens including Salmonella, Listeria, and E. coli, as well as the most common foodborne and waterborne viruses that sicken people and animals.

The project will provide a roadmap for developing tests to identify pathogens and help trace their origins more quickly. The new genome database also will enable scientists to make discoveries that can be used to develop new methods for controlling disease-causing bacteria in the food chain.

"This landmark project will revolutionize our basic understanding of these disease-causing microorganisms," said Harris Lewin, vice chancellor for research at UC Davis.

The sequencing project is critically important for tackling the continuing outbreaks of often-deadly foodborne diseases around the world. In the United States alone, foodborne diseases annually sicken 48 million people and kill 3,000, according to the CDC.

"The lack of information about food-related bacterial genomes is hindering the research community's ability to improve the safety and security of the world food supply," Weimer said.  "The data provided by the 100K Genome Project will make diagnostic tests quicker, more reliable, more accurate and more cost-effective."

"We see this project as a way to improve quality of life for a great many people, while minimizing a major business risk for food producers and distributors," said Mike McMullen, president of Agilent’s Chemical Analysis Group.

A consumer-focused article about the project is available on the FDA website.

(This article was condensed from a UC Davis news release. Read the full press release and watch a video of Bart Weimer giving an overview of the project.)