Cohnella: The Cold-Season Soil Microbe That Keeps Working When Others Go Dormant
Cohnella is a genus of spore-forming soil bacteria in the Paenibacillaceae family. Some species fix nitrogen from the air, and others break down plant fiber into soil nutrients. Its tough spores let it survive cold, drought, and heat that stop more delicate microbes. One species, Cohnella laeviribosi, is among the 291 DNA-verified microbial species in Elm Dirt Plant Juice.
By mid-December my garden in Kansas City looks like somebody pulled the plug on it. Brown stalks, a little crust of frost on the last of the kale, nothing moving at all.
It's awfully easy to assume the soil underneath has quit for the year too, but it hasn't, and one of the reasons is a tough little bacterium with a name that sounds like a law firm. Welcome back to our microbe spotlight. This week it's Cohnella.
A quick confession before we dig in. The first draft of this post said Cohnella wasn't in our Plant Juice, and it was just about ready to go out that way until I sat down with the DNA report and a highlighter and went through it again, one species at a time. Page seven. Rank 124. Sitting right there the whole time.
Meet the microbe: Cohnella. A spore-forming soil bacterium from the Paenibacillaceae family. It has been found around pepper, plantain, corn, and alfalfa roots, in Arctic tundra, and in a volcanic area in Indonesia.
What's in this guide
What Is Cohnella?
Cohnella belongs to the Paenibacillaceae family. That makes it a close cousin of Paenibacillus and a more distant relative of the Bacillus bacteria you may have seen listed on a garden product label.
What sets it apart from most soil microbes is the spore.
If you've never given a bacterial spore much thought, picture a seed in a packet: the cell dries itself down, wraps up in a tough coat, and sits there doing basically nothing (for a very long time, if it has to) until the soil gets warm and wet enough to be worth waking up for.
It also turns up in some pretty odd places.
- Around pepper roots in China, where researchers found Cohnella capsici.
- Cohnella plantaginis came out of the soil packed around plantain roots.
- Alfalfa fields in Taiwan gave us Cohnella formosensis.
- Cohnella arctica? Tundra soil in Norway's Svalbard islands, roughly 800 miles from the North Pole.
- And Cohnella laeviribosi, the one in our bottle, was first pulled from a volcanic area in Indonesia.
No single species handles both the tundra and the volcano, as far as anybody knows. The genus just gets around.
Several Cohnella species were found in the rhizosphere, that crowded strip of soil hugging the roots.
Cohnella Species at a Glance
| Species | Where it was found | What it's known for |
|---|---|---|
| Cohnella plantaginis | Plantain root-zone soil, China | Fixes nitrogen |
| Cohnella capsici | Pepper root-zone soil, China | Fixes nitrogen; forms spores |
| Cohnella formosensis | Alfalfa root-zone soil, Taiwan | Breaks down plant fiber (xylan) |
| Cohnella arctica | Arctic tundra soil, Svalbard, Norway | Cold-tolerant; grows from 39°F to 86°F (4–30°C) |
| Cohnella laeviribosi | Volcanic area, Indonesia | Heat-loving; grows from 99°F to 140°F (37–60°C); in Elm Dirt Plant Juice |
Why Spores Matter in Winter
Most soil microbes are fragile. Let the ground get cold enough or dry enough and a lot of them slow to a crawl or die off, and whoever makes it through has to rebuild their numbers come spring.
Spore-formers skip that whole ordeal.
Now I owe you the less flattering part. The Cohnella in Plant Juice likes it hot, and I do mean hot: C. laeviribosi grows best right around 113°F, which is steamier than most hot tubs, so it is not out in your January flower bed getting anything done. It's sealed up in its spore coat and waiting, same as a bean seed in the kitchen drawer.
The cold one in the family is its cousin C. arctica. It'll grow at 39°F, about what your refrigerator runs.
Put those two next to each other and you've got the whole case for soil diversity inside a single genus. But I'm getting ahead of myself.
(If spore-formers are your thing, Clostridium is another one worth meeting.)
What Cohnella Does for Your Plants
Not every Cohnella species does the same job. Which is sort of the point.
- A couple of them fix nitrogen. C. plantaginis and C. capsici were both described as nitrogen-fixing species, which means they pull nitrogen out of the air and turn it into a form roots can actually use (Wang et al., 2012).
- Others go after fiber. C. formosensis breaks down xylan, the stringy stuff in plant cell walls, and a strain of C. laeviribosi makes a xylanase enzyme as well (Bioresource Technology, 2010). That's part of how last summer's tomato roots slowly become food for next year's soil.
- Several species were found living in the root zone, close enough that plants can use what they release.
- Spores keep it banked in the soil all year.
If nitrogen fixing plus decomposition sounds familiar, it's the same story we told about Rhizobium and Bacillus. Want the full trip from air to leaf? Our nitrogen cycle guide walks through it without the textbook headache.
Old roots and leaves don't disappear. Something has to eat them.
Cohnella in Plant Juice
Plant Juice is independently DNA-sequenced by BiomeMakers, and the report runs page after page, with a cell count for every species it finds. I'm a chemical engineer, so of course I read the whole thing. Usually twice. Three times, this go-round.
It's got company, too. The same report turned up a handful of its Paenibacillaceae relatives:
- Thermobacillus composti, at about 24,500 cells per mL
- four Paenibacillus species, P. edaphicus and P. montaniterrae among them
- a pair of Brevibacillus species
Of all 291 species, about 80% are associated with nitrogen release. You can see what we test for on our nutrient and microbial analysis page.
No one microbe makes or breaks a garden, Cohnella included. The crowd is what you're after.
Do Soil Microbes Work in Winter?
They do. A lot slower, but they don't clock out.
The study that surprised me most looked at boreal forest soil frozen at about 25°F, where microbes were still breaking down cellulose, and it's the kind of result that sends an engineer back to reread the methods section just to be sure she understood it right the first time.
Other researchers have shown cold-tolerant soil bacteria helping tomato plants handle chilling stress. Some cold-adapted strains are even being studied as phosphate fertilizers for cold climates.
We've already spotlighted one of those cold-season workers. Chryseobacterium is a cold-tolerant bacterium that helps keep roots growing in tough conditions, and it's in Plant Juice too.
So think about what that means in your own backyard. A soil with hundreds of species has somebody suited to whatever the weather throws at it, whether that's a soggy April or a November that can't make up its mind. A bed that's been living on synthetic fertilizer has a lot less folks home when it turns cold. There's more on that in living soil vs. sterile soil.
Frost on the surface doesn't mean the soil's gone quiet.
How to Keep the Tough Crew Thriving
You can't run to the store for a jug of Cohnella, and you really don't need to.
What you can do is make your soil the kind of place hardy microbes want to move into and stick around, and most of that work happens in fall, before the ground locks up.
- Cover bare soil before it freezes. University of Minnesota Extension notes that mulch slows heat loss and cuts down on freeze-thaw swings. Shredded leaves work great, and they're free. Our mulching how-to has the details.
- Stop yanking spent annuals out by the roots. Snip them at the soil line instead and leave the roots behind for the fiber-digesters to work on all winter. I used to pull every tomato plant, root ball and all, and I cringe a little now.
- Compost, worm castings, or Ancient Soil (a Class A certified compost) spread in fall brings in a wide mix of microbes. Not sure where to start? Try how to amend garden soil in fall.
- Plant Juice adds microbes directly, 291 verified species with Cohnella in the mix.
- Go easy on synthetics. Salt fertilizers and pesticides thin out the very diversity you're trying to build, which we dug into in our organic vs. synthetic soil health study.
An afternoon of this in October pays off all winter long.
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Real Gardeners, Real Results
I'd rather you hear it from them than from me, especially this time of year. A few folks who used Plant Juice on plants that had a rough go with the cold:
Linda L.
After a surprise Texas cold snap, all the blooms fell off. The leaves looked healthy so I watered it with my Elm Dirt. Just days later it is once again covered in beautiful blooms!!
LeAnn G.
A few days after plant booster everything greened up. My roses had some issues after a previous vicious winter. I also applied Elm Dirt a few days later for extra love. It’s quite wonderful to see this change! Great products, easy to apply.
Doreen C.
I was losing my 50 year old Christmas cactus, this past winter in the house was rough on it. The leaves were falling off, the whole plant was limp and there had been no new growth for a long while. I watered it twice with Elm Dirt Plant Juice and it is a brand new plant. The leaves firmed up and the branches perked up and I’m seeing new growth all over the plant. I’m so happy with the outcome. The only reason I liked the product instead of loving it was because of the smell. But the smell won’t keep me from using it, it is that good for plants. I’m using the Plant Juice on all my plants. It’s a little pricey but it’s worth it.
Jeannie D.
I used it on my porch ferns and within a short time the whole thing was standing up straight. Some garden plants are reviving after the cold weather better then ever.
Rated 4.65 out of 5 across 1,793 Plant Juice reviews. (Doreen's right about the smell. It's alive. Living things smell.)
Frequently Asked Questions
What is Cohnella bacteria?
Cohnella is a genus of spore-forming soil bacteria in the Paenibacillaceae family, the same family as Paenibacillus. Species have been found in the root zones of pepper, plantain, corn, and alfalfa, and in places as extreme as Arctic tundra and volcanic ponds. Some species fix nitrogen, and others break down plant fiber.
Is Cohnella in Elm Dirt Plant Juice?
Yes. Independent DNA sequencing by BiomeMakers identified Cohnella laeviribosi in Plant Juice at about 10,100 cells per mL, one of 291 verified microbial species. The same test found several relatives from the Paenibacillaceae family, including Thermobacillus composti and four Paenibacillus species.
Do soil microbes keep working in cold weather?
Most soil microbes slow down as soil cools, but activity does not stop completely. Cold-tolerant bacteria keep cycling nutrients at low temperatures, and researchers have measured microbes breaking down cellulose in soil frozen at 25°F (-4°C). Spore-forming bacteria like Cohnella survive the cold in a dormant state and restart when soil warms.
How does Cohnella help plants?
Some Cohnella species, such as Cohnella plantaginis and Cohnella capsici, fix nitrogen from the air into forms plants can use. Others, such as Cohnella formosensis, produce xylanase, an enzyme that breaks down plant fiber. Because several species live in the root zone, that work happens close to plant roots.
Is Cohnella laeviribosi a cold-tolerant microbe?
No. Cohnella laeviribosi is heat-loving. It was first isolated from a volcanic area in Indonesia and grows between 99°F and 140°F (37–60°C). It gets through cold weather as a dormant spore. The cold-tolerant member of the genus is Cohnella arctica, isolated from Arctic tundra soil, which grows at temperatures as low as 39°F (4°C).
How do I keep beneficial soil microbes alive over winter?
Keep the soil covered with mulch or shredded leaves, leave the roots of spent annuals in the ground, add compost or worm castings in fall, and avoid synthetic salt fertilizers and pesticides. Mulch buffers soil against freeze-thaw swings, and organic matter gives microbes food to draw on when temperatures rise.
The Soil Never Really Sleeps
So when you look out the kitchen window in January and the garden looks dead, remember that it isn't.
Down in the root zone the spore-formers are sealed up and waiting on spring while the cold-tolerant bacteria keep chewing slowly through last year's roots and leaves, and the richer and more varied your soil is, the more of that quiet work gets done without you having to lift a finger or even put your boots on.
Best deal in gardening, if you ask me. They work the cold shift while I stay inside with coffee and a seed catalog.
Your next step: join our email list for one small growing win each week, or keep exploring with what's living in a tablespoon of healthy dirt and living soil explained.
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Sources & further reading:
Cho et al., "Cohnella laeviribosi sp. nov., isolated from a volcanic pond," IJSEM, 2007 (PubMed).
Jiang et al., "Cohnella arctica sp. nov., isolated from Arctic tundra soil," IJSEM, 2012 (PubMed).
Wang et al., "Cohnella plantaginis sp. nov., a novel nitrogen-fixing species isolated from plantain rhizosphere soil," Antonie van Leeuwenhoek, 2012 (PubMed).
"Cohnella capsici sp. nov., a novel nitrogen-fixing species isolated from Capsicum annuum rhizosphere soil" (PubMed).
Hameed et al., "Cohnella formosensis sp. nov., a xylanolytic bacterium isolated from the rhizosphere of Medicago sativa L.," IJSEM, 2013 (PubMed).
"Novel intracellular GH10 xylanase from Cohnella laeviribosi HY-21," Bioresource Technology, 2010 (PubMed).
"Microbial mineralization of cellulose in frozen soils" (PMC).
Subramanian et al., "Cold Stress Tolerance in Psychrotolerant Soil Bacteria and Their Conferred Chilling Resistance in Tomato," PLOS ONE, 2016 (link).
Rizvi et al., "Psychrophilic Bacterial Phosphate-Biofertilizers," Microorganisms, 2021 (MDPI).
University of Minnesota Extension, Mulching for soil and garden health.
Plant Juice species data: independent BiomeMakers DNA sequencing of Elm Dirt Plant Juice.
Lauren Cain
Founder & Chemical Engineer · Elm Dirt, Grandview, Missouri
Lauren started Elm Dirt after her 6-month-old daughter grabbed fistfuls of backyard dirt and ate them. As a chemical engineer and a mom, she couldn't just shrug it off, so she dug into the science of what was really in garden soil. That rabbit hole led her to build a fertilizer line around beneficial microbes instead of synthetic chemicals, and to have every batch independently DNA-sequenced so she knows exactly what's in it. Today Elm Dirt products are used by home gardeners, rose show champions, and organic growers nationwide.