Soil bacteria perform many essential tasks to enable plant growth, including cycling nutrients and fixing nitrogen. To explain the fascinating things that researchers have discovered about soil bacteria in recent years, my guest on this encore presentation is gardening columnist and author Jeff Lowenfels.
Jeff writes a weekly gardening column for the Anchorage Daily News, and he’s a retired natural resources attorney who earned the title “America’s Dirtiest Lawyer.” He also previously hosted a gardening radio show and Alaska public television’s most popular show, “Alaska Gardens with Jeff Lowenfels.” He’s a former president of the Garden Writers Association of America, a GWA fellow and a GWA Hall of Fame inductee. His “Teaming” series of books includes “Teaming With Microbes,” “Teaming With Fungi,” Teaming With Nutrients” and the subject of this discussion, “Teaming With Bacteria.”
Jeff Lowenfels is the author of the “Teaming” series of books, including “Teaming with Bacteria.” (Photo by Judith Hoersting courtesy of Timber Press)
For a comprehensive rundown of our discussion, you can read the show notes from the original airing of our conversation. Otherwise, keep reading for an abbreviated recap and updated Links & Resources for this episode.
Meet Jeff Lowenfels
Jeff grew up in the Hudson Valley region of New York State, in Westchester County, where he planted, weeded and mowed and picked fruits, flowers and vegetables on his father’s 8-acre “gentlemen’s farm” until he left for Harvard College in Cambridge, Massachusetts, to study geology. He continued his studies in Boston at the Northeastern University School of Law, where he earned an environmental law degree
Jeff is also the founder of Plant a Row for the Hungry, a public service program he began in Anchorage that has since gone national and has resulted in millions of pounds of garden produce being donated to feed the hungry every year. He was a guest on the second season of my public television program “Growing a Greener World®” to talk about Grow a Row for the Hungry for an episode on how gardeners can help the needy.
How Soil Science Has Advanced Since ‘Teaming with Microbes’
Since the publication of “Teaming with Microbes” in 2006, researchers’ understanding of soil science has grown tremendously.
We knew in 2006 that plants take photosynthetic energy and use about 30%, 40% or even 50% of that energy to produce exudates that drip out of their roots. “The exudates are designed by the plant to attract bacteria and fungi,” Jeff explains.
These microorganisms eat the exudates, and then nematodes and protozoa come along that eat bacteria and fungi. The waste they excrete is in the form of nutrients that plants can easily absorb through their roots.
“What they poop out turns out to be plant nutrients in usable form,” Jeff says. “In other words, the microbes put a charge on it. And if you read my second book, ‘Teaming with Nutrients,’ you’ll see that that charge is necessary for these things to go inside the plant.”
It was years after “Teaming with Microbes” was published that the important role of mycorrhizal fungi was confirmed. Now we know that 90% of plants form a symbiotic relationship with mycorrhizae.
“The fungus feeds the plant in return for getting these nutrients,” Jeff says.
The system that he described back in 2006 was a soil-mediated nutrient system. He says the idea is that nutrients went into the soil, and from the soil, they moved into the plant. The mycorrhizal system that soil scientists later discovered works by nutrients going from the soil into the fungi, and then the fungi trading those nutrients with roots for exudates.
More recently, Jeff says, scientists gained a greater understanding of rhizobia, a type of nitrogen-fixing bacteria, which forms a relationship with legumes. The plant attracts the bacteria, which create a home in a root hair. As the bacteria take up residence there, they pull nitrogen from the air for the plant’s benefit. And when plants die, they release that nitrogen to feed future generations of plants.
To promote good bacteria on and in the plants in your garden, Jeff advises making sure your soil has plenty of organic matter to support a healthy biome. Sterile soil and sterilized seeds disrupt the natural systems of plants.
Plants release exudates through their root hairs to attract beneficial bacteria and fungi. (Photo Courtesy of Timber Press)
Endophytic Bacteria
Endophytic bacteria are bacteria that reside within plants for at least part of their lives and provide benefits to the plants. These bacteria assist in hormone production, which helps the plant in forming leaves, setting fruit, and dropping fruit, among other processes.
Some endophytic bacteria can move from one plant, like grass, to another, like a dandelion, kill the dandelion, and then return to the grass. These bacteria could eventually be cultivated and sold as a biological control for weeds.
“It’s a whole new frontier,” Jeff says.
Endophytic bacteria inhabit the flower of a plant and become enclosed within the seed coat as the flower forms seeds. This is how the bacteria persist in the next generation of plants.
“Then when the seed germinates, they hop back into the soil, and they’re available to help the plant,” Jeff says. “The same bacteria that infected — if that’s the right word — corn 400 years ago, exists on corn today because it’s in the seed, and it jumps back out again.”
There are also endophytic (endo=inside, phytic=plant) mycorrhizal fungi and endophytic yeast.
Bacteria move in and out of plants at the root hairs. (Photo Courtesy of Timber Press)
How Understanding Bacteria Will Improve Agriculture
By understanding how plants can naturally fix their own nitrogen, we can reduce the reliance on harmful chemicals in agriculture.
“Research has shown that if you’re using chemical nitrogen, you are reducing your nitrogen produced by bacteria,” Jeff says. “And, you know, plants have been doing this for thousands and tens of thousands of years. Why do we think we’ve got a better system?”
When plants receive chemical nitrogen fertilizers, they no longer need to signal to beneficial nitrogen-fixing bacteria for assistance. To encourage beneficial bacteria in your garden, Jeff recommends ensuring your soil is rich in organic matter, which supports a healthy biome. Sterile soil and sterilized seeds can disrupt the natural systems that plants rely on.
He points out that compost and vermicompost have different bacterial compositions, and one may be more effective for certain plants than the other. The type of compost input determines the bacteria present. Jeff advises that if you want to grow grass, you should use compost made from grass clippings, and if you want to grow tomatoes, you should use compost made from composted tomato plants. (A note to add: if your tomato plant had a disease, it’s best to discard it rather than compost it, as the pathogens can persist in the compost.)
“Teaming with Bacteria” is the fourth book in Jeff’s “Teaming” series. (Photo Courtesy of Timber Press)
I hope you enjoyed my conversation with Jeff Lowenfels on “Teaming with Bacteria.” If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
How have you encouraged beneficials microbes in your garden? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 116: Understanding the Soil Food Web, with Dr. Elaine Ingham
Episode 117: Compost, Compost Tea and the Soil Food Web, with Dr. Elaine Ingham
Episode 184: More Must-Have Books for Every Gardener
Episode 270: Plant Science for Gardeners, with Robert Pavlis, Part I
Episode 281: The Chemical Age: How Tools of War Became Agricultural Chemicals
Episode 282: The Vital Role of Soil Bacteria in the Garden, with Jeff Lowenfels
Episode 287: No-Till Gardening and The Living Soil Handbook, with Jesse Frost
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joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
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joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
Earthbound Expeditions: Discover South Africa with Joe Lamp’l
GGW Episode 220: Gardening for the Hungry
“Growing a Greener World with Joe Lamp’l” podcast Ep. 029 with Jeff Lowenfels
Jeff Lowenfels on Instagram: @gardenerjeff
Jeff Lowenfels on X: @gardenerjeff
Jeff Lowenfels | Alaska Gardening and Growing column
“Teaming with Microbes: The Organic Gardener’s Guide to the Soil Food Web” by Jeff Lowenfels and Wayne Lewis
“Teaming with Fungi: The Organic Grower’s Guide to Mycorrhizae” by Jeff Lowenfels
“Teaming with Bacteria: The Organic Gardener’s Guide to Endophytic Bacteria and the Rhizophagy Cycle” by Jeff Lowenfels
“Teaming with Nutrients: The Organic Gardener’s Guide to Optimizing Plant Nutrition” by Jeff Lowenfels
“He Wrote a Gardening Column. He Ended Up Documenting Climate Change.” | The New York Times | By Zach St. George
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