See what the package says the spacing should be for them apart. Then just use this spacing for them in between rows as well.

Here is a link that might be useful: The Corner Yard

I planted fava beans last year and this year in the non-square foot portion of my garden; I think the package spacing directions were 12". If I were to plant them in my square foot area, I would try at both one and two plants per square.

Germination rates have been excellent, with the Windsor variety that I used - even with my October planting from seeds purchased last year. I did not pre-soak, though I did water well after planting. I also used a rhizobium innoculant (Garden Combination).

In my experience, fava beans were a lot of work for a low yield. The main reason I planted them again this October was for use as a cover crop. The flowers are beautiful and attract beneficial insects, and the beans are very tasty. But there were not that many beans per pod, and it was a lot of work first to shell the bean pods and then to remove the skins before cooking to eat. I grew quite a few fava beans in the spring planting (3 rows, with each row 12' long) and only harvested enough for two or three servings, so be prepared to devote a lot of space to this plant if you want to get a good yield. However, perhaps the yield per plant would be better in a square foot garden, with a good soil mix.

Now that I'm seeing this 12" spacing reiterated, I'm wondering if there was a typo on my package. I bought a dwarf variety from Pinetree and the package spacing is listed as 2". I planted them all today - 9 squares of plants a little more than 2" apart, making it 16 plants per square, or 192 plants total. If the regular sized fava plants are to be spaced 12" apart, 2" sounds awfully crowded, and with the long DTM, it sounds like I may have just screwed myself out of 9 squares that could have been dedicated to something that'd grow and be more productive. Oh well, live and learn! I'll cross my fingers that they come up, and that the 2" wasn't a typo.

My package said 8-12 inches apart. I ended up planting one per square. I did use soil inoculant. The packet I bought turned out to contain only 9 seeds, so I planted them all. I will see how they do.