Put the tuber in a hole several inches deep with the “eye” on the tuber facing up. The eye is the point on the shoulder, or crown, of the tuber from which the plant grows. If you are planting a number of dahlias in the same location, they should be separated by about 2 feet to give each plant room to grow.

Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/dahlia/tips-dahlia-planting.htm