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It is a smoke tree/ smoke bush. More than what species it is, it is the USE in the landscape that determines how a plant is trimmed, the first choice being if it is a tree form or a shrub form. In the first place, in a good landscape design, a plant would not be used unless its form/shape/size fit the purpose of its position in the landscape.

We can't see through it, but can see a house behind it. I presume you want this in the tree form ... with a raised canopy .... instead of a big block of foliage (canopy) at the ground level.

For myself, I am picky about trunk structure since it ends up being a major part of the tree. Here, we cannot see it. (It is hidden within the foliage.) If it is acceptable to you, then you'll just accept it an move forth with developing the rest of the tree. (If it was not acceptable to me, I'd cut the tree to the ground and regrow it, making it how I like it ... which is usually with at least 1/2 dozen trunks in a bouquet style arrangement.)

The difference between a trunk and branch/limb is that the former is more vertical than 45* of the horizon. The latter is more horizontal than 45* of the horizon. At the halfway point of the tree's overall height, remove all branches limbs all the way to the ground, keeping all trunks. Don't leave any stubs.

After the tree is done blooming, you could slightly round the canopy top by snipping off any long tips of upper branches. You're done for the year.

Royal purple smoke tree, trim it how you want it to look. Try snipping everything off up to a foot or two and see if you like the way its looking, if so keep trimming higher until you get your desired look. Be careful of over correcting when doing this, its easy to keep trying to get the branches even and before you know it you've trimmed higher than you ever wanted to. They're pretty tough little buggers so trimming it to the ground to get a new trunk shape wouldn't hurt it but it would take at least 4-6 years to get a tree look again depending on your zone. Post pics of the result.

-Brad

More than what species it is, it is the USE in the landscape that determines how a plant is trimmed

This is false, over the years entire manuals have been written and printed about pruning woody plants that contain encyclopedia sections devoted to what is involved with all the different kinds - how each particular species or set of related types needs to be handled in order to have attractive outcomes, wherein the plants do not end up looking bizarre, butchered or tormented.

For instance it has been my experience that when Cotinus coggygria is cut down low, to stumps it comes back broad, flattish and sprawling - if such were done in this instance the plant would be all over the lawn and concrete path, with it having been planting right by the edges of both.

Tree-like shrubs reacting to severe pruning in this manner do so because the hormones that make the upper parts grow vertically have been removed with the parts that have been cut off. And the low sections left behind have to restore these hormones before the original upright growth will reappear.

Andrew should do a web search for a phrase like "cotinus pruning" and study what comes up before proceeding. It should also be noted that the sap of this plant can be an irritant for some individuals, so Andrew should avoid contact with it when working on the plant. Unless it is already known that Andrew is not affected.

"... but it would take at least 4-6 years to get a tree look again .." I don't know how you figure that with an already established root system. Typically, a plant like this cut to the ground delivers 50-60% of its height back in the first year, but with more trunks. (It's presumed the goal is multi-trunk, since that's what we're looking at now.) Later in the year, at the end of the growing season, or early next year, the tree can be limbed up to half its height with the result being: the "tree look."

"This is false, over the years entire manuals have been written and printed ..." As with doctors and lawyers who incorporate Latin into their jargon in order to seem mysterious to the public, the horticultural industry is likewise infiltrated here and there with obfuscators. My objective is to make information as simple to understand as possible. For freestanding woody plants, the basic form options are as follows:

(The pictograms are making no comment about size or details.)

Everything beyond that is no more than a derivation (of which there are innumerable) on one of those forms.

The first decision you're going to want to make, Andrew, is if the tree's value to you is because it serves a purpose as a positive contributor within your overall landscape ... or if you're merely trying to cultivate it as a botanical museum collectible whose value is irrespective of its surroundings (your yard.) The commonly available advice is geared toward the latter position, where the plant is a royal princess and exists for its own sake ... in a botanically oriented garden where plants ARE the royalty, that would be fine. But in landscape oriented garden -- people's yards -- plants are primarily servants. They need to comply with the needs and priorities of the property owner. Which means what they won't exist at all unless they're serving a function, which could include enhancing the appearance of a house.

Most of the time, in order to be in compliance with people's needs, tree canopies will be over one's head, not in their face. That's a good goal to work toward here.

Andrew, you say the Cotinus is overgrown but you don't say what exactly is wrong with it in your eyes. It seems to be doing a good job of screening the neighbouring houses and doesn't appear to be blocking any paths. It does, however, appear to be impinging on the conifers and probably shouldn't have been planted there in the first place, being potentially too big. Do you just feel that shrubs 'need' pruning or do you have a specific vision for this one? I'd agree with Brad. Decide how you want it to look and cut accordingly. Do you want a shrub or a tree? A natural looking form or a shaped one? As long as you prune back to a stem and don't leave stubs you can do pretty much as you wish. Not everyone necessarily wants the same shape in their trees andshrubs. And bear in mind that if you keep pruning the tips you won't get the 'smoke'.

Re hard pruning of Cotinus coggygria. It is common here to cut them back yearly to stumps because the purple ones especially experience so much winter die back. I've never seen them regrow "flattish" and "sprawling." What I see is a gorgeous, upright flush of deeply purple growth; they don't of course flower, but that color! I do the same with my yellow leafed one, 'Golden Spirit'. Just gorgeous.

Andrew, you can find video on Youtube showing how to prune this plant.