I would do what I call a star pattern: 2 in the front row, 1 in the middle, and 2 in the back row. Put the white one in the middle row, and the second white one in either the first or third row. Space the plants about a foot apart.

Keep in mind in the first year you're probably not going to get that full, lush "mingling" look, but be patient - that will happen.

White tends to make most other colors look brighter. I have a mixed planting of "White Swan" and "Magnus" coneflower, and I really enjoy it. :0)

I think white and pink coneflowers look pretty together. The mix of Powwow berry and white together would probably give you a more uniform look to the plants. You could try a zig-zag pattern, 3 whites in back and 2 pinks in between in front.

I have Powwow berry, but not white. I've got other whites - 'Primadonna', White Swan and Baby swan and assorted pinks, Prairie splendor, Powwow, Bravado, and a seedling I've selected, and they are sort of randomly mixed. Most were started from seed.

Here's white swan with some random E. purpurea taken a few years ago-
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