I’ve used the 3 Sisters method a few times, and there are some things that tend to get left out of the description that might be important:
1. Once all those vines grow, you won’t be able to walk through the patch. If all 3 are varieties that don’t need harvested until the plants dry down, and they don’t need any tending until then, this might be fine. But if you need to get in there, for any reason, it won’t work.
2. Spacing. When using this method, plant in hills a few feet apart. If you try to plant it in rows like normal corn, then the beans and squash will get shaded out. They might produce something, but they won’t be as healthy as they should be.
3. Harvesting. Assuming you grew a dry bean (since there’s not much chance of reaching them to pick a green bean), they will be tangled in with the corn stalks and squash vines. The untangling will mean the harvest takes longer, is more frustrating, and leads to more dropped in the process.
I find it easier to plant in blocks, and just rotate the blocks to get the soil benefits. This makes both the growing and the harvesting much easier!
I have never really tried the planting in circular mounds. My grand daughter likes the Italian Roma beans, and they are bush beans.
I do inter crop these three some times in my raised beds. They are 3’ x 8’. So I have three rows. I plant the back row in corn with one seed in the middle of a sq. ft. The middle row, I plant the seed diagonally from those.
Still in the middle of the sq. ft. measured from front to back, but midways between the other seeds. In between each of those I plant beans till I get to about a quarter of the way along the length and that’s where I put a squash seed, and again at the 3/4 mark.
Then I plant the next row of corn, and again plant some beans in between the corn. Seems to work and I’m able to get plenty of green beans harvested at the same time.