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feed the soil: my experiment with mycorrhizae

mycorrhizae illustration copyright Bio-OrganicsI ALWAYS SAY “feed the soil, not the plants,” which for decades has meant to me to turn in compost—lots and lots of compost, and then more—and every few years a topdressing of organic fertilizer. Lately I’ve been curious what more I can do, as stressors ranging from dryspells to disease test me and the plants. I’d often read about inoculating the soil with mycorrhizae–myco means fungus and the suffix means root, so literally root fungi, a word used to indicate a symbiotic relationship between the two. Until last fall, at garlic-planting time, when I purchased $49.50 worth (enough for the garlic, plus my whole vegetable garden) I’d never experimented hands-on. More about my mycorrhizae adventure:

The tipping point had been meeting Graham and Layla Phillips, who had recently taken over Bio-Organics, founded in 1996 and one of the first companies to commercialize mycorrhizal agricultural products (disclosure: they have advertised on A Way to Garden).  We got to talking, and I pestered them with my usual endless questions–and then bought myself that jar of a blend of viable beneficial organisms from their online store.

I didn’t just take their word for how it all worked, however; I dug deeper. Extensive Texas A&M research over more than 25 years reports that the benefits of mycorrhizae include plants that are more vigorous, with increased drought and disease resistance and the ability take up more nutrients and water. They may also need less pesticides because of their overall better response to stress. (Mycorrhizae have even been used by Aggie researchers on Texas lignite coal-industry land to try to revitalize it after mining, but I’m hoping your garden isn’t in that condition!)

Even deeper background: Mycorrhizae weren’t “invented,” not by Bio-Organics or Texas A&M any other current commercial producer or research institution. They’re a group of naturally occurring soil organisms, one or more species of which most plants depend on to thrive (different plants, different preferred species).  The interaction is mutualistic, not just one-way: The fungi use the Carbon produced by the plants to support their own functions, in turn helping the plant to reach farther into the soil by creating an extensive network or web of fungal filaments–they look like root hairs–called hyphae.

When I first read about using mycorrhizae, it all sounded a little like pre-treating beans and peas with Nitrogen-fixing inoculant, or taking probiotics for a healthy gut—you know, natural, or holistic. But of course those examples are uses of friendly bacteria, not fungi like the mycorrhizae. (And you know how I’m fascinated by the power of fungi.)

Much of the commerce in mycorrhizae to date has been geared to agriculture and the nursery industry.  Grapes, for instance, are very dependent on mycorrhizae (as are roses, for another example), so vineyards are one industry that extolls their virtues. Spurred by Texas A&M findings, wholesale nurseries, including giants like Monrovia, have begun inoculating their potting soils, seeking potential benefits such as reduced transplant issues and faster establishment.

Such industries hadn’t initially come to mycorrhizae seeking a ”save the earth” solution, says Graham (read more about the Wharton law-and-business graduate in this “Philadelphia Inquirer” story), but rather a better economic equation in crop production. For instance, they may harvest at a younger age (as with the grapes), or reduce fertilizer costs, or otherwise improve the bottom line.

Now other potential customers—including more gardeners—are coming asking about natural solutions to growing success.

Like me with my curiosity about fine-tuning my soil-feeding mantra. And so when the raised beds here can be worked in a couple of weeks, I’ll continue my experiment with mycorrhizae, by using the rest of my supply.

I’d love to hear if you’ve begun your own experiments with these fascinating microbes and what your experience has been.

mycorrhizae 101, the basics

I ASKED GRAHAM PHILLIPS a few key practical questions about using mycorrhizae, in this short Q&A:

Q. When do I apply mycorrhizae?  Do I re-apply every year?

A. Mycorrhizal products are often used by gardeners when sowing seeds, when transplanting, or to inoculate a bed before planting, working them into the top 4-6 inches. Inoculated soils will actually improve year after year, so it’s a sustainable product.

Q. Do I till in coming seasons?

A. We recommend no- or low-till practices, so the network of filaments, or hyphae, can develop and flourish year to year. Keep using your compost.

Q. Do I use fertilizer as well?

A. Many synthetic plant foods, especially fast-acting liquids, harm microbial activity in the soil and create fertilizer-dependent plants, so we don’t recommend using them. We say that the fungi are not an “add-on-” to a chemical-fertilizer routine, but best used “instead of.” We recommend ongoing use of compost, compost tea, cover crops, and if needed, small amounts of dry organic fertilizers that release slowly.

Q. Does mycorrhizae work on all plants?

A. There are a few plants that are said to be non-mycorrhizal, meaning they don’t form the mutualistic relationship with the microbes. These include blueberries and other ericaceous plants such as azaleas; brassicas (cabbage, broccoli, mustard, etc.); spinach and beets.

Q. Where do I store leftover product, or can I?

A. You can store it for two years, preferably in a cool, dry place, but it will last longer.  After two years the spores begin to degrade as time passes, but many will remain viable–you would just have to use a little more each subsequent year.

(Top illustration courtesy of Bio-Organics.)

  1. Roger Giovinazzo says:

    P. Allen Smith has been extolling the virtues of mycorrhizae for years, specifically through the use of ProMix potting mix and garden amendments. So I have been mixing in a bale in any new bed I make and added a bag from Espoma as well. I haven’t done any experiments like growing a tomato with and without amending so I can’t say how well it “works”. I have read where it does no good in a healthy soil so I have always been left wondering, is it worthwhile. I’m counting on you, Margaret, for the definitive answer. (:

  2. At our organic perennial nursery and garden center we have been using mycorrhizae fungi when potting for two years. In Canada, the product is called MYKE. We also have been trialing and testing it for three years in our botanical gardens. From our experience, we have seen exponential growth and root development using mycorrhizae fungi. It does cost more to incorporate into our regimen and it does effect our bottom line, but it is a huge benefit to the root growth and plant life. With greater and faster root development we have seen the plants winter over more successfully. The product we use for perennials contains endomycorrhizae fungi. The formula with ectomycorrhizae and ectomycorrhizae is used for shrubs and evergreens. The company we purchase our product from advises that the roots make direct contact with the mycorrhizae. There are also certain plants that cannot be colonized by the mycorrhizae fungi; for example lupins, alyssums, orchids, broccoli, cabbages, beets, turnips, spinach, radish…etc. Also any high NPK applications of synthetic fertilizers will destroy the mycorrhizae. We use only organic, granular or liquid fertilizers (4-4-4) and compost. It is all about the soil. The mycorrhizae form a symbiotic relationship with the plant roots and this in turn makes it easier for us to grow more successfully.

    1. margaret says:

      Thanks for the first-hand nursery-tested feedback, Lorraine. Such an interesting subject.

      I’ll look up the Reading talk, Sarah. What Graham suggested to me (when I posed the skeptic’s view on mycorrhizae) was to try a side-by-side control test — same crop and conditions, but in two separate beds, one a control (without inoculation) and the other the test bed, sort of a mini-version of what Texas A&M researchers (and other university types) have done.

  3. Sarah Wilson says:

    I attended a talk last year given by a professor at Reading University in the UK. He had also been conducting experiments with micorrhizal fungi and had found that it didn’t little to benefit plants. He stated that the fungi are living organisms and may not survive the processes of packaging and storage associated with transporting them and offering them for sale on a commercial scale. He also believed that because each plant has its own species of symbiotic fungi, the chances of you purchasing a bag of fungi that contains the fungi specific to your plant, it being alive and it then establishing a relationship with your plant were extremely low. Just thought I’d put that out there.

  4. Beth Urie says:

    Margaret – have you noticed improvements in the issues you had been seeing in your garden? I love seeing mycorrhizae, often under or through old mulch. But I had been told the fungi were so specific to their locations that an all-purpose fungal inoculation was probably not worth the investment. There has been much debate on the various blogs/forums that we all frequent. Sometimes, you go for it anyway, in the interest of the experiment. And to add to the data. Let us know, and thanks for sharing all, as you do.
    P.S. I plan to inoculate a new garden area, right under the its ‘lasagne method prep’ period. Then use no-till methods.

  5. Roger Giovinazzo says:

    Here is what Linda Chalker-Scott from Washington State University and contributor to Fine Gardening magazine has to say about it under her “garden myths” heading-http://www.puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Mycorrhizae.pdf She says “nay” to amending.
    She is well worth checking out everybody.

  6. Deirdre says:

    I did not know that about the Ericaceae. My garden is at LEAST 60% Ericaceae. It’s a good thing I haven’t wasted any money on mycorrhizeae.

    PS woodland soils are dominated by fungi. Non woodland soils are dominated by bacteria. Giving fungi to meadow plants (sun loving perennials) is a waste of money. They are adapted to bacterially dominated soils.

    If you build it, they will come. Pile organic matter; compost in sunny borders, wood chips in shady garden on (not in) your soil. The mycorrhizae and bacteria will come.

  7. Jan says:

    How it was explained to me was that the soil had to be in pretty good shape to begin with to provide a good environment for the mycorrhizae to function. The example was if you took 10 people from a Caribbean island and dumped them out in Chicago in January, how many would still be there 2 weeks later?

  8. I also say Nay, along with Linda Chalker-Scott to amending or inoculating your garden with mycorrhizal fungi, but I say Yes to adding it to the roots only when planting. That’s it, never again. We have done trials with tomatoes, lettuce and thousands of perennials side by side and have seen the difference firsthand. Compost helps to increase the mycorrhizal fungi activity.

  9. Lisa Mertins says:

    I’ve begun my yearly battle with the Devil Grass, however, I find that it has a lovely amount of mycorrhizae attached. I wonder what happens to the good stuff when I eliminate the grass. Will it be happy without its evil partner?

  10. mikeinportc says:

    When I worked for a greenhouse/florist business, we inoculated poinsettias with mycorrhizae, and some other beneficials, to prevent root diseases, that commonly plague poinsettias. It definitely helped. The dead , among 5000+ pots ( ~,14,000 cuttings) were a countable number. ;) We watered it in, about two weeks after transplanting the cuttings, when they were firmly rooted into the planting medium.
    Maybe we should have used it on some other things, especially summer-grown cut flowers. ( Tough to keep them sufficiently watered.)

  11. Karlie says:

    I am a firm beliver in the benefits of mycorrhizae when planting. It has improved the survival rate of my shrubs and trees when used in the planting hole. I have not added any to my flower or vegetable beds – may give that a try this year.

  12. BooksInGarden says:

    Love the topic and explanation. Mycorrhizae are just beginning to be properly recognized for their contributions to plant and ecosystem health. I have had a lot of success with their use.
    Small nitpick on picture: most of the root system of all plants, including trees, in all soils is concentrated in the top 12 inches of soil.

  13. So timely! I’ve been reading about Mycorrhizae and we are implementing it at the nursery/landscape company where I work. Think I will order some. Thanks for the info Margaret!

    1. margaret says:

      Welcome, Mario. Interesting to hear your company is going to be using it, too. So much to learn, isn’t there? :)

  14. Beverly, zone 6 eastern PA says:

    If using Mycorrhizae would somehow lead to less use of synthetic fertilizers, I’m all for it! Folks need to be educated on how to care for their soil. Not enough people know what is harmful and/or why it is harmful.

    My gardening neighbor reaches for the blue stuff whenever she can, then laments the steady decline of her large landscape. In contrast, I am running 8 compost bins, maintaining a thriving one-third-acre plot nearly completely cultivated and do not have one speck of synthetic anything for the garden.

    I would love to see a photo of the mycorrhizae. I feel certain I must have come across them at some point while digging here for 23 years….

  15. Beth says:

    I have always felt guilty when turning over the soil to add compost because I have read that it’s best not to disturb the microrrhizae. I am wondering where the balance lies between the two. Thanks for the article, there are so many strange and wonderful things going on beneath our feet!

  16. Susan Galyon says:

    Maybe we have all seen the rizobial networks in our compost? White, thread like structure that often seen to have a gel stickiness? I think annual applications of compost would innoculate for many species but maybe not all. A good source of informaiton for me has been the book Teaming with Microbes, The Organic Gardener’s Guide to the Soil Food Web by Jeff Lowenfels and Wayne Lewis. The one I have is the revised edition published in 2010. For me, an organic grower of 30 years experience, one of the revelations was feeding the microrrizae in my soils. I have started my own little experiments with various combos of sources of carbon for the fungal growth. I would reccommend the book to gardeners who love to make soil. I don’t grow great plants; I make great soil. The rest is up to God. Spring is just around the corner in NW Georgia. Yeah!

    1. margaret says:

      I have the book, Susan — I didn’t even think about it, until your reminder. Thanks. I set it on the shelf in my office and sort of forgot! :)

  17. Hello Margaret,
    I have had personal experience with mycorrhizae for years now. Mycorrhizae is both beneficial fungi and bacteria. My initial exposure was to Dr. Elaine Ingham at Oregon State University and Hendrikus Schraven in Seattle. Jeff Lowenfels & Wayne Lewis put out a book (recently revised) through Timber Press: Teaming With Microbes. Cascadia (in Seattle) is working on some tests, as well; I believe their tests are with oxygenated compost tea. My personal experiences have been with using tablet form mycorrhizae obtained at the Olympia Farmers Market, maybe 7 years ago. I plugged 4 of the tablets into the root zone of a Japanese Maple with early verticillium wilt. I trimmed the affected branches from the tree and watered in the tablets. The tree has never looked back and is still healthy today. I’ve used this same method on tree peonies that were suffering from a fungal infection. I have also made my own oxygenated (read: stirred) compost tea and then at optimum strength, sprayed roses with blackspot and cruciferous plants. I would swear by this method. That said, I sat in on a talk by Linda Chalker-Scott, who remains unconvinced because she has not seen adequate testing. I hope that some of these resources help you. Welcome to the mycorrhizae club! (It’s a bit of gardener’s religion here in the PNW.)

  18. I forgot to mention that when I work with landscape contractors, they buy mycorrhizae in bulk and add it to the planting hole of nearly all plants. (Some plants don’t benefit from it.) We’ve had excellent success with client plants!

  19. Sandie Anne says:

    I have a maple tree in the front yard that isn’t doing so well. How would I apply these mycorrhizae? Would I have to dig down to the roots? I would really like to save this tree.

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