Orchids sit at the front of the line. More than 20,000 orchid species live with a fungal partner, and that is the largest single plant group named in the extension literature. After the orchids, the best-studied mycorrhizal host plants are forest trees, legumes, and a long list of garden vegetables and herbs. No source ranks those groups against each other, so read the list as four well-documented partners rather than a scoreboard.
The research gives you links and measured growth responses. It does not give you a winner. Soil chemistry shifts the answer as well, and it shifts it a lot. The University of Alaska Fairbanks puts the key role of these fungi below about 50 parts per million of soil phosphorus. Above about 100 parts per million in its Alaska soils, the plants show little need for the fungi at all. So one plant can gain a great deal in lean ground and almost nothing in a bed you have fed hard for years.
Trees carry the longest record. Ectomycorrhizae alone cover more than 4,000 fungal species, and they work with the pine, oak, birch and myrtle families. That is why mycorrhizae for trees shows up in forestry and mine reclamation work far more than in flower beds. The fungi raise both water and nutrient uptake in trees, and nitrogen and phosphorus move the most.
The field numbers are the useful part. They show what a good pairing does in real ground rather than in a lab dish, and the size of the gain swings hard with the site.
That dune grass trial is worth a second look. The same transplants also put on 81% more root length, 64% more height and 53% more tillers over those 20 months. Poor sand and low phosphorus are the setting there, which is the setting the fungi answer best. The poplar and alder numbers come out of coal-mine revegetation. That trial set mature forest soil against immature soil rather than isolating the fungi.
Legumes get a second payoff on top of the usual water and nutrient gain. The fungal link raises nitrogen-fixing nodule capacity, so the rhizobia in the roots have more room to work. Peas, beans, clover and vetch all sit in this group. That is nodule capacity, which is not the same thing as a measured gain in nitrogen fixed.
For the kitchen garden, mycorrhizae for vegetables pay off most in the same lean, low-phosphorus soils. An Alaska snap pea trial put inoculated plants about 10% taller than plants left alone, which is real but modest next to the dune grass figures. Onions, leeks, tomatoes, peppers, squash and carrots form the same kind of link, and so do most culinary herbs. Brassicas are the main holdouts, so an inoculant has little to offer cabbage, kale or broccoli.
Match the fungal type to the plant before you buy anything, because mycorrhizal host plants do not all take the same partner. Many conifers and oaks form ectomycorrhizae, the type that sheathes the outside of a root tip. Most herbaceous crops and grasses form arbuscular mycorrhizae, which grow inside root cells instead, while orchids have a category of their own. Some plants host both. A packet aimed at herbaceous crops will do nothing for a pine seedling, and the reverse holds too.
Run a soil phosphorus test before you spend money. Above about 100 parts per million, even a strong host plant has little use for an inoculant, and your dollars do more good on compost or mulch.
Read the full article: Mycorrhizae: What Works and What Is Hype
