You are looking at two different plants :-) Smoke bush is Cotinus coggygria, native to Asia and typically grows to about 15' if left unpruned. Smoke tree is Cotinus obovatus, native to the US and while often still very shrub-like, can get to be 35' tall. Both can be trained into tree forms and smoke bush is sometimes sold already trained this way in nurseries. 'Grace' is a hybrid between the two species and can get quite large - 25' is possible. But it also has a pretty wide, spreading habit often with multiple stems from the root crown so how likely it will respond to being trained into a tree form is a bit of a guess. You will need to start small if that's your intent. The flowers are the "smoke" effect - pruning back top growth on any sort of routine basis will typically result in a lack of flowers/smoke. Since you don't say how large this area is, it's impossible to say if 3 of these planted together are too many :-) But even if trained to a single trunked tree form, these do produce a healthy canopy spread - about as wide as tall, if not wider for the smoke bush; about 20-25' for the smoke tree. Plan accordingly.

Everything is making so much more sense to me after Peonysmoke's post. I too have never had my purple smokebush bloom. The first 2 years it got massive winter dieback from being in line of the winter winds. Then I moved it to another, more sunny and less windy location. Apparently it liked the move because it grew really tall last year (but no smoke). This year it looks like I may get some blooming, but only from lower limbs (the growth that is older than 2 yrs). Go figure though - I bought a "Young Lady" smokebush at the end of last fall (who can resist a 1.5 gallon shrub at $2.50?). I left it in the pot and covered it with straw for the winter. The tips looked like they had died back, but I held off pruning. Lo and behold, it has leafed out everywhere and looks to be getting ready to bloom.

Penny I now prune mine when dormant in the spring before new growth starts. This next year I will prune it down to about a foot off the ground to get all new growth. I will not get any bloom next year, because it will not bloom on the new growth. It now has quite a bit of dead wood and is generally misshapen. Al

I'll bet you it's getting too much water.It doesn't need the same amount of water as Hydrangeas,so if you plant one again,have it in another,drier section of your yard.