I'm occasionally asked about test protocol for trials of mycorrhizal fungi on various plants, often by researchers.
Here's my suggestions for the procedures to follow:
1. If you have handled the jar of inoculant, wash your hands before setting up the tests. Just a few microscopic spores can pretty easily accidentally get where they are not supposed to be.
2. Set up all of the "control/without" plants first to avoid any chances of cross-contamination with spores on hands or tools, and be sure they are in separate water trays if the test is indoors. If the test is being conducted on garden, landscape, or farm plantings, try to maintain several feet of distance between test and control plants as the mycorrhizal fungi hyphae can transfer from one root system to neighboring roots.
3. For large-scale fields, orchards or berry plantings, somehow flag either the "with" or "without" plants and don't rely on memory. Also, be sure that work crews know to not remove your markers. In most situations, differences will be noticeable within a few weeks but longer-term differences in growth, yields, and earliness of production may also be observed.
4. Greater differences between test and control plants will be seen in poorer soils or those where synthetic fertilizers have been used for many years. Such soils typically do not have any resident populations of native mycorrhizal fungi. However, even if there are indigenous fungi in the soil, it may be useful to introduce the several strong species in our inoculants at planting time, especially if you are dealing with plants that are not native to your area.
5. Don't skimp on inoculant if you are evaluating the product for possible regular use in nurseries or for repeating plantings. The first and most important issue is whether or not inoculations create noticeable differences. If you see good results, then you can experiment with more cost-effective smaller dosages to decide how little can be applied per plant.
6. Plants with mycorrhizae on their roots will not necessarily be taller than chemically-fertilized plants, but you should observe that they are more sturdy, with thicker trunks and shorter distances between branches. It is hard to generalize about this, as the responses to biologically-active soils by various plants will differ. For turf grass, it may be better drought-resistance and for wine grapes, it may be production at an earlier age. Superior disease resistance is a common result for all plants.
I would encourage setting up comparison plantings whenever possible, and would enjoy hearing your observations. I sometimes notice that our products have been used in articles published by university researchers, but anyone can set up a few with-or-without pots or leave a few check plants uninoculated.
Best wishes for the new year!