Quick and Easy Guide: On-farm AM fungus inoculum production

Following is the crib-notes recipe for producing beneficial AM fungus inoculum on-farm. For more details on the when, why and how, read A Complete How-To.


The following list will produce 16 “Grow Bags” of inoculum, enough to make 200 or 400 ft3 of inoculated greenhouse potting media depending on the dilution ratio (1:9 or 1:19) of inoculum:potting media used in the final step.

Bahiagrass seed (sources for bahiagrass seed can be found on the internet, for example: http://agriseek.com/market/p/Pensacola-Bahiagrass-Seed.htm)

Conical plastic pots  (we use RLC-4 Pine Cells from Stuewe and Sons, Corvallis, OR 97333)

Coarse sand such as swimming pool filter sand (240 in3 for 80 seedlings)

Ground cover fabric (16 Grow Bags fit on a 1.2 m x 3.6 m or 4 ft x 12 ft section)

16-7 gallon “Grow Bags” (one source is Worm’s Way, Bloomington, IN 47404)

4-4 ft3 bags of vermiculite

4 ft3 of compost

In order to maximize mycorrhizal proliferation and colonization of the host plant, the inoculum bags should be setup outside as soon as possible after the last frost. Some work is necessary before this date. The finished inoculum will be ready for use the following spring.

4 months before the predicted last frost:

Germinate bahiagrass seeds (or other host seeds) in vermiculite or seed starter.

Order any needed materials.

3 months before the predicted last frost:

Transplant bahiagrass seedlings into conical plastic pots filled with 1:3 soil:sand mixture (volume basis). In order to avoid introducing pathogens, we suggest using sterilized field soil. Another option is to use soil from a natural area of the farm or from a field that has not been used within the past 2 years to grow the crop that will be inoculated.

As soon as possible after the last frost:

Set up the inoculum production area by covering an area with the ground cover fabric. This will provide a clean, open area that makes maintenance easy. It will prevent weeds from growing around the bags and contaminating the inoculum with weed seed.

Set up the grow bags:

Mix compost and vermiculite in chosen dilution. A basic recommendation for yard clippings compost from municipal facilities is a 1:4 compost:vermiculite ratio (volume basis).

Fill bags ¾ full with mixture. Roll the lip of the bag down to just above the level of the mix.

Add 100 cm3of field soil as the “inoculum starter” and mix well.

Pool 4-5 soil samples taken from the surface to 10cm (4 in) deep. Sieve out roots and rocks.

To avoid introducing pathogens and to obtain a diverse sample of AM fungi, take samples from a natural area of the farm or from a field that has not been used within the past 2 years to grow the crop that will be inoculated.

Transplant 5 bahiagrass or host plant seedlings into each bag.

During the growing season:

Weed and water the bags as needed. The mycorrhizae will proliferate as the plants grow.

Frost will kill the bahiagrass and the mycorrhizae will overwinter naturally outdoors in the bags.

The following spring:

Harvest the inoculum:

To keep the inoculum clean, cut off the dead bahiagrass leaves and discard.

Shake the compost and vermiculite mix from the root ball into a bin. This mix will contain the mycorrhizal spores and hyphae.

Cut the roots into short segments (less than 1cm or ½ inch) and mix into bin. The roots contain the mycorrhizal vesicles.

Mix the inoculum into your potting medium:

Use a 1:9 inoculum:media mix (volume basis) for flats with cells of 50 cm3 or smaller. For larger cells a 1:19 mixture should be sufficient.

Amend your greenhouse fertilization regime to avoid P-sufficient plants that will resist colonization:

Conventional farmers: Try to achieve a P addition of 3 ppm or less for no more than three fertilizer applications per week. Apply P-free solutions at other times if necessary.

Organic farmers: If your potting medium requires additional fertilization, use a low P source. If your potting medium contains all the nutrients needed during the greenhouse culture phase, no modifications are recommended at this time.

Adapted from David Douds’ “Checklist of steps for the on-farm production of arbuscular mycorrhizal [AM] fungus inoculum”
in his eOrganic article  On-farm Production and Utilization of AM Fungus Inoculum.
This material is based upon work supported by the U.S. Department of Agriculture, Agricultural Research Service, under Specific Cooperative Agreement Number 58-1935-5-524. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

10 Responses to “Quick and Easy Guide: On-farm AM fungus inoculum production”

  1. Corazon Cook

    I would like to teach the farmers in the Philippines how to use mycorrhiza. Vermiculite is one of the materials needed for the inoculum production. Can it be substituted with coconut coir because vermiculite might be difficult to obtain.

    How do you measure the success of the inoculum production? Do you check the mycorrhiza production under a powerful microscope?


  2. amanda

    Dr. David Douds did look at alternatives for vermiculite and says that although they didn’t use coir, he thinks it could be used.

    Dr. Douds also included the following regarding measuring success of propogation:

    Researchers evaluate the success of the inoculum production process by isolating and counting the spores of AM fungi produced in the compost and vermiculite mixture. This requires a dissecting microscope, sieves, and a centrifuge. Also, roots can be observed for colonization by the fungi. This requires a variety of chemicals and the same dissecting microscope.

    However, the method has always been successful in our hands, so one can safely assume a propagules density of approx. 25 per cm3.

  3. Ton Lagerway


    Have become very much interested in Mycorrhizae and intend to grow some in an “old disfunctional” freezer.
    I can get hold of Bahia grass seeds in Australia to sow in the sub-tropical climate prevailing in the Gold Coast hinterland!

    I would like to utilise the inoculated soil produced by the grass as the soil used in the punnets for the production of new seedlings for planting out.

    Would the mycorrhizal propagules remain viable in the harvested & stockpile as (inoculated) compost for the next 1/2 year when stored in plastic bags under the house where the temperature remains moderately cool even during our hot summers?

    If so, this would (could) allow for the production of a crop of “Bahia Grass inoculated compost” every 1/2 year or so.

    Would inter-planting additional species of plants amongst the Bahia Grass allow/promote the maintenance of a diverse range of Mycorrhizal species with which I intend to inoculate the first batch?

    Another thought:

  4. Nick Rose

    I live in San Mateo, California and have a about 2600sqft of land that has lawn, roses fruit trees and a small vegetable area. The house was built in 1947 and no major disturbance to the soil has occurred since then except for a new 1000sft back lawn that was put in around 2013. I have not used any chemical fertilizers, herbicides since 2013, no pesticides have been used on the site for probably decades. I know the only true way to find out if I have mycorrhizae in the soil is by having it tested for. But with that said is it possible that mycorrhizae have re-populated the soil. On the NRCS websoil survey shows the area is Urban land-Orthents, reclaimed complex. The land use to be tidal flats but the area was filled with around 5ft of fill.

  5. larry

    seeing how i have been gardening in the same spot for 5 years, with varied results from year to year. i remembered using a fungi when i had worked for a local landscaper. mostly for trees and shrubs, so i did not make the connection to vegetable gardening until recently. i enjoyed reading these web pages. i am curious though? why Bahiagrass for AM fungus inoculum production? would local varieties of grass be acceptable? or a plant with a fast growing high density root system be acceptable as well? i understand that local AM is prefered, but would using an biologically active product and mixing with local spores work as well, better or worse?

  6. larry

    also is there further research in progress. i have seen other sites with research articles on the use of mycorrhizal fungi, though most of those do not have the time in, or the backing of the usda. thank you for your time and consideration

  7. Carlos Loeza

    This is interesting considering bahiagrass seed has grown abundantly throughout central Florida. I wonder if Bill Mollison’s ‘imitating the forest floor’ by creating raised beds over the bahiagrass is an on-site production of fungus inoculum.
    Here is a transcript from his show in the 90s:

    Stand in one place and lean out a little bit. Reach around you in a circular motion and that’s your garden. Covers 12sq meters. Where you can reach from standing in one place is 12sq meters. Maybe if you’re small, you need two of them, opposite of each other.
    Those gardens are the least for the greatest production beds. Six feet across, maybe larger. A single sprinkler can cover all of that. You can water the whole garden from that point.

    If you don’t have a sprinkler, you can hand water by hoses. If you don’t have that, you have to sink unglazed clay pots and keep them full of water. Refill them every 4-5 days. That is the most economical way to garden. It leaks out water and grows an area about 3 feet across.

    Paper all over with newspaper because we’re in America. If we’re in India, we do it with banana leaves. Throw with straw on top.

    Have a bucket of soil from a nice place with nice soil (dug it out from pig sty or scraped up from forest floor).

    Three or four layers:
    Straw or Dry Banana leaves
    Newspaper overlapped (so there’s ever no more weeds)
    Planting seeds – Make Lens about 3 inches thick in the middle of good soil and on that you sprinkle fine seeds (patch of carrots or radishes)
    Thick in the middle about 15inches across. You make as many patches of fine seeds as you like.

    Another one is you push your hand down and force a little hole open and leave a handful of soil in it. In that you plant your seedlings and large seeds like beans.

    For root crops, you put them down on top of newspaper. Punch a hole in newspaper and put your artichokes and your tubers.

    You can newspaper your little standing spot and put thick sawdust on top.

    So the garden is weed free. You haven’t put a lot of effort in.

    A bucket, a few bales of straw and your seeds and tubers. About 40minutes.

    If you’re going on a plan
    Plant in spring, thats your next six months. Plant again in late summer to early autumn.

    Don’t have to put any worms in. If you have a worm within five miles, you get it.

    Straw height doesn’t matter (9-12 inches). You can use loosened hay, that is very high protein and makes garden immensely successful.

    Put about 2-4inches of hay (alfalfa) around the bottom and put ordinary straw.

    If you forget to water it, invest in automatic water machine and harvest your food.

    Doesn’t matter if its on concrete. If it is in concrete, put 3-4 inches higher of straw.

    People in wheelchairs can also, just do it on a table. Paper + Loosed hay + 2-3 bricks high, hand them their seeds and bucket of soil. Two tables will make too much food for one person. One table is plenty.

    We didn’t do any heavy work. We didn’t plant any weeds so No weeding, no tilling and no digging.

    The crops and the worms together work down the soil in three years. So you gotta remulch; spend 40min every three years.

    End of Gardening. Although that sounds a bit careless, its a result of an awful lot of trial and error to get this recipe right.

    -Bill Mollison

    Instread of straw you can use leaves or flat stones. What you have to do is cut the light out to the Earth’s surface so there’s no chance of weeds germinating.

    If by any chance a weed comes out, just push it down and put more straw on it.

    It will keep your salads and ordinary vegetables. Squashes, cucumbers. You can put a trellis around the back (using sunflowers). Its a windbreak and also another crop.

    If you’re on high planes and its screaming cold, build a four tire wall and face that to the sun. It makes a warm and sheltered environment.

    Lettuces go on top. Lettuce disappears if straw goes across it.

  8. vrheadset

    At round £27 in the UK, these aren’t the most affordable VR glasses
    we’ve tested, nor are they the very best in terms of performance.

  9. Ethan Smith

    Thank you for the tutorial. We are planning to begin this system next year on our farm in Montana. Since we failed to set up grow bags early enough to have innoculum finished for next year, we are going to try to colonize our Bahia grass in grow bins in a University greenhouse over the winter. We will let you know how successful we are.
    Have you tried perlite as a substitute for vermiculite? I understand the physical differences between the two in terms of surface area,CEC, water holding, etc, so I would assume that vermiculite would be a preferred substrate for colonization. Perlite can be up to 300% cheaper here, and would thus be ideal in a cost context. Any input or comments based on experience would be great. Thanks!

  10. Baran Tan

    it is possible that you can explain this experiment by video?

    If so that would be an amazing source for the farmers from another countries


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