I did an experiment last year on several legumes: beans, runner beans, cowpeas, green gram (mung) and garbanzos. Soybeans were included also, but rabbits ate one of the rows. You will note that I did NOT test garden peas (I will this year).

There are different inoculants for each legume species, and many combinations are commonly sold. Beans (snap or dry, limas, and runner beans) and peas generally use the same inoculant, in a "garden combo". Vignas (cowpeas, mung, adzuki) need a different combination. Soybeans require their own, as do garbanzos.

Two rows were planted, one treated with inoculant, the other untreated. For all but the cowpeas, there was no noticeable difference in yield. The bacteria are, apparently, already present in the soil... either that, or the inoculant had only a negligible effect.

The cowpeas, however, produced more & larger pods on the treated row. And as an unintended result of the experiment, I also had not treated my yardlongs with inoculant, for the first time since I have grown them (they are the same species as cowpeas). It was their worst year ever, even with varieties that have proven themselves reliable... one I've grown for 15 years, with never a failure.

My soil is fertile, and I had used inoculants on the same ground for many years (with the exception of the garbanzo). On poor soils, or where beans & peas have never been grown before, inoculant might have more pronounced results - at least for the first year. But based upon my own observations, I wouldn't worry too much if you plant without it - except for cowpeas & yardlongs, for which I highly recommend its use.

Gardenlad, I hope you're lurking out there somewhere... you win. ;-)

Pete