Three Sisters
According to Iroquois legend, corn, beans, and squash are three inseparable sisters who only grow and thrive together. This tradition of interplanting corn, beans and squash in the same mounds, widespread among Native American farming societies, is a sophisticated, sustainable system that provided long-term soil fertility and a healthy diet to generations.
Corn provides a natural pole for bean vines to climb. Beans fix nitrogen on their roots, improving the overall fertility of the plot by providing nitrogen to the following years corn. Bean vines also help stabilize the corn plants, making them less vulnerable to blowing over in the wind. Shallow-rooted squash vines become a living mulch, shading emerging weeds and preventing soil moisture from evaporating, thereby improving the overall crops chances of survival in dry years. Spiny squash plants also help discourage predators from approaching the corn and beans. The large amount of crop residue from this planting combination can be incorporated back into the soil at the end of the season, to build up the organic matter and improve its structure.
followers do this
Note for self: corn = maize, beans = green beans/runner beans, squash = pumpkin.
beans in the historical case were most likely black beans or pinto beans (the kind you buy dry at the grocery store), but really any kind of bean will work, especially if it likes to climb (they’re all the same species, Phaseolus vulgaris). You do have to make sure the maize grows faster than the beans (or plant beans a couple weeks after the maize), otherwise the vines can actually pull down the maize before it has a chance to get established. And you have to have enough water and nutrients in the soil to support all that growth, or whichever plant is most efficient will steal all the resources and the others will suffer.
Grain+legume in general is an Extremely Valid system, so a lot of cultures have developed variations that fit their own environment and food preferences. In Mali, you might find sorghum+cowpea (black-eyed pea), up in the Andes barley+fava beans, in Southern Africa maize+groundnut (peanut) or maize+pigeon pea, or for A+ high quality animal feed (and/or soil conservation/restoration) oats+vetch… the list goes on.