
Certified GKH Gardening Expert
Zinnias and cosmos are wonderful for attracting butterflies and other pollinators. Depending on the varieties, there could be a big height difference, so determine the mature heights before planting. The distance between will also depend on the varieties chosen, but they both have the potential to spread width-wise, so 2 feet should be ample.
https://www.gardeningknowhow.com/ornamental/flowers/zinnia/growing-zinnia-flowers.htm
https://www.gardeningknowhow.com/ornamental/flowers/cosmos/growing-cosmos.htm