I've been growing onions for a couple of years. The only problem I can see would depend on how close you're planting them. If in the same row, the beans may crowd the onions, both under ground and above! If too close, the beans may block the sun, and the roots crowd the onion bulb. If "in the next row", you may be OK.

I can tell you from experience that PEAS do not grow well with onions. I planted a long row of peas last year, and in a few places I also planted some onion sets in little groups. As the season wore on, it was clear the peas near the onions did much worse. At one point the peas near the onions only had 1/3 of the growth as the peas farther away. They never grew into the robust vines of the peas that were not near the onions, although they did produce some.

So after that, I do not plant onions near legumes. And by near, I mean it was within about 12 inches that seemed to have an effect.

My bush beans next to the onions did poorly compared to the ones further away. Good to know about the 12" observation, greenmulberry.

I read about this after noticing it, so you have the benefit of reading and our experience, steve.

Any other observations about poor companions as striking as this? Maybe I can save myself a poor crop of something else.

Hepatica

I've had pole beans do poorly when surrounded by onions. Now I surround the place where I plan to plant tomatoes with the onions. They seem to like each other.

Now I know other folks say cabbage and tomatoes aren't a problem but the one time I planted them together they both weren't as good as before. Now if I follow cabbage with tomatoes, I don't have a problem.....just when next to each other.

I also plant basil around the tomatoes. They both like all the water. I keep the basil clipped down until the tomatoes set and then I let it grow tall and hide them from the sun. I've only had one hookworm in 4 years but I'm not sure if the basil is really the protection. I just do it so I can have pesto and tomato sauce at the same time. And it smells so nice when I harvest tomatoes.

I plant onions around every thing I grow...I have onions and peas growing happily inches from each other...same with beans...never been a problem...

I guess Texans are so much larger than life that even that pesky old pea-n-onion thing doesn't apply! But you're the first I've heard that didn't find it a problem, Ruth.

It's especially severe with walking onions probably because they are perennial and so really saturate the soil with the exudate that the peas apparently detest. Fortunately, as noted above, the exudate doesn't seem to travel far.