Hi, Whaas!
I have my quickfire in amended clay soil and have had it for 4 years now. It's in 2 hours of direct noon day sun & puts out 1 or 2 longer branches (by about a foot) each year, which the plant seems to "grow into" the next year. So...I'm expecting it to get to 8 '. It's about 4' tall by 6' wide now as it is under probably less than optimal conditions. Helpful?

MCG

Intersting its that much wider than tall. I would be so pleased if they get 6' X 6' or bigger.

Both my areas are slightly amended. One group is on a slight slope, they get about 8 hours of sun.

The other group is planted on a very flat area. They get about 10 hours of sun.

I pruned the dried/dead flower heads to the next bud in late spring (right as the buds where swelling).

They all grew about 6".