They can get tall when they have a fence to grow on. The point is don't plant in rows but a tench next to fence. Eight foot fence is a great length to pick and plant. If you have more seed just make the trench wider. Peas vine and grow up on each other and will actually kill out other plants if they don't have a fence to grow up. All Plants need air as well as sun, dirt , water Even air in the ground so it's not to compact.
I think it's the square foot garden book that has several ideas for fence or archs. Some are very clever and decorative.