I planted 10 burning bushes in a bed in my back yard a few years ago. They do not grow terribly quickly. I think they're probably a foot taller now than they were three years ago. I have not fertilized them since I initially planted them (discovered fertilizing newly planted shrubs was a mistake!), and I don't prune them either. So I'm sure I'm not encouraging growth as much as I could. They have filled out very nicely, and they're are gorgeous in the fall! By the way, don't be surprised if they don't "burn" the first year.

Annld,
Thanks for the response!

I have some "dwarf" ones in my front yard that are about 6 ft tall now.

You may find yours will grow faster in SE PA. Mine are under the full shade of a pine tree, in a very dry location.

Additionally, you can look forward to eventually having little seedling burning bushes here and there....

It is best to go easy on the fertilizer with newly planted shrubs. Good soil, and full sun and it may grow about 3-5" a year. However it will take several years for it to get 5-6ft.

I looked at mine again today, and I think they've grown more like 1 1/2 to 2 feet in three years. I can definitely see that the ones that get the most sun have also grown the most. They really are beautiful. I highly recommend them!