Dr. Ted's Chunky Style Myco-bits

The plants that become mycorrhizal

Ted St. John, Ph.D.


See the myco-bit on types of mycorrhizas for part of the story here. This part is intended to quickly figure out what kind of inoculum your plants may need.

In the majority of cases the right kind is arbuscular mycorrhiza (AM), often just called endomycorrhiza. In this group are all grasses, palms, almost all bulb plants, anything related to roses, apples, peaches, pears, strawberries etc. (the rose family), most tropical plants apart from orchids, and the great majority of horticultural species. Almost all crop plants, apart from the mustard and spinach families, have this kind. The majority of wild plants, including shrubs, wildflowers, and broad leaf trees, have this kind. A few conifers do, especially the ones related to redwoods, cedars, and junipers. It is easier to list the non-host species (no mycorrhizae) than the ones that have AM.

The forest timber trees (apart from redwoods and cedars) are ectomycorrhizal (ECM). This includes all pines, firs, Douglas firs, spruce, larch, oaks, birch, beech, and some willows and cottonwoods, which have both ECM and AM. A few nut crops have EM, including chestnut, hazel, and sometimes walnut and pecan. There are recent reports that very old grape vines might be EM, although grape is normally a good AM host.

Manzanita and madrone have the arbutoid type, and there seems to be no commercial inoculum for those. Blueberry, huckleberry, heather, and related plants have ericoid mycorrhizas, and there is also no inoculum for those.

Orchids have their own kind and there is no need to inoculate them. Commercial orchid production is done with special chemical media that bypass the need for mycorrhizas. Grown orchids usually have rejected the fungus and are non-mycorrhizal.

Some plants do not become mycorrhizal at all- the "non-hosts". These include the mustard family (cabbage, radish) and the spinach family. Some related wild plants and many kinds of weeds also lack mycorrhizas. Inoculation is often part of a program to fight weeds, since non-host weeds have more trouble competing with mycorrhizal plants.

In your list of plants, look for the ones that may be ECM, arbutoid, ericoid, and non-hosts. Since the mycorrhizal status is known with certainty for only a fraction of the world's plant species, many recommendations will have to be guesses. The best guess is usually AM.

The soil network, in combination with healthy mycorrhizal host plants, is very important in resisting weed invasion. There have now been a good number of field projects that have successfully fought off weeds, where other methods that did not involve inoculation have consistently led to nightmare weed infestations. Inoculation is often not enough in itself, but must work with rapidly growing native plants and in many cases, some means to temporarily immobilize nitrate, such as a layer of straw or wood chips.