A quick Google search gave a couple of good links.
Both recommend severe cutting back each winter for intense color and bloom, regrows rapidly to around 5'.

http://www.greatplantpicks.org/index.php?page=display&id=2389&searchterm=all
http://www.floridata.com/ref/C/coti_cog.cfm

Royal Purple grows like nothing I've ever seen before.

Right now, my Royal Purple bush (tree) is about 12' tall,
and I've cut it back (severely) each of the past two years.

My wife walked out into the yard and said, refering to my Royal Purple ... "Where did that come from ?"

I told her that the plant had been there a couple years, at least.

She followed up by saying ... "Well, it sure didn't look like that, did it ? (refering to it's size).

Allocate space if you grow this one.

I also have a younger Velvet Cloak.

It doesn't seem to have as rapid a rate of growth as Royal Purple. And it's foliage is a nice red in the fall.

It blooms on previous year wood, so cutting back will eliminate flowers all together. IMO, 'smokes' on purple/burgundy cultivars are not as showy as on a green cultivars, so if colorfull foliage is your the only goal, you may cut it to the ground and have 5-6' tall shrub by the end of the season. Every other year cutting will produce 12-15' tall multitrunked small tree
Look stunning if underplanted by yellow leaved spireas or chamaecyparises.
Early June (for the lack of better picture)
{{gwi:280682}}

ego45,
You state that smoke bushes bloom on previous year wood, but the Floridata site states that they bloom on new growth:

"Since smoketree flowers on new growth, it can be cut to the ground each winter and grown as a cutback shrub."

Is it that they bloom on both new and old growth, or is Floridata wrong?

Here is a link that might be useful: Floridata

Well, I have no clue why Floridata (usually reliable sourse) made such statement, but here is a quote from not less respected sourse, Missouri Botanical Garden,
'If bloom is not a concern, stems may be cut back hard in early spring each year to a framework to induce growth of vigorous new shoots with slightly larger than normal leaves. Such hard annual prunings will control size, but most likely at the expense of profuse flowering. Hard pruning is more often done on the purple-leaved cultivars.'
My personal experience is in full compliance with above statement. I guess, 'most likely' are a key words.

Here is a link that might be useful: Kemper's Cotinus page

Thanks for the links and pictures. Cutting it back is probably more of a necessity for me - will likely be killed back anyway. That it blooms on new wood is also my understanding so realize I will likely not see blooms. Looks like ultimate size seems to very depending perhaps on cultivar.

FYI - this is the article from my local botanical gardens.

Here is a link that might be useful: Olbrich Gardens

if it were me.. i would go to the LOCAL garden .... measure and note how big it is... and then look close into the tree.. and see how far they cut it down ... and make appropriate determinations ...

a mature specimen will grow bigger than a transplant, based on its roots ... so take that into account ... speak with the keeper of the LOCAL garden if there is a need for more info ..

ken

By cutting back, it's meant to cut almost to the ground, not just trim. In other words, treat it as we do buddleia in cold climates and let it make all its growth from the ground up. The idea is to get long shoots with extra large leaves but no flowers. I planted one this summer at the back of a perennial bed and plan to cut it all the way back next spring.

Yes - I am talking about cutting it back to the ground. The local gardener indicated that his grew to 15' in the article above which, as I said, seemed like a lot of growth for one year. So, just trying to get some input from others as to what they thought. Thanks!