I find the foliage gets to be 21/2-3 ft. The plant is very nice but does not bloom from June - Sept. at least not for me, more like late August into Sept.

This is one of my favorites to have in the middle of mostly low growing native perennials and ferns. For me the plant can be as Peren indicated, usually three feet. Mostly it blooms in late summer, but this year I am seeing flower stalks on some, but not all, of the plantsl. I usually have to wait until it is late in the season to gather seeds, I wouldn't worry too much about how close you plant them as other things seem to grow all around them without a problem.

My plants are also about 3 feet tall, with the blooms at 5 feet. They are blooming now. No current pics, but here's one from July 16 last year, those lacy plants behind the variegated hostas:

Just returned from the Cullowhee Native Plant Conference, where I purchased two different plants that are almost identical to Actaea racemosa: A. americana and A. rubifolia, which likes sweeter soils. They both bloom later than A. racemosa. At a casual glance, they all are very much the same. Maybe the ones I have that bloom so late are the above, since they were rescued from mountain property?? Now I will be on a "mission" to look at the ovaries, which is one way to distinguish. Most references on the internet still have the old Cimicifuga listing. I already knew about dolls eyes, A. pachypoda since I found it on my own mt. property years ago. So much to learn!