What's the reason for the area being narrow? If it means it is also shady, then it might not do very well, as junipers need full sun.

Otherwise, it is up to personal preference - if you think it'll look nice with a trunk with no low branches, go ahead.

Resin

seems to me all the Spartan junipers I've seen have been single stem plants but with dense foliage and a narrow habit. Even old specimens in cemeteries. Elvie's questions make me wonder what that plant looks like.

Marshall

Although it is being used to sell what is supposedly a Chinese juniper the Spartan trademark actually covers a fast-growing J. scopulorum (or J. virginiana) cultivar reaching at least 20' tall. If this space is only a few feet wide it is going to get tight at some point unless you shear the tree to control size. Even then you won't be able to hold it back indefinitely. And based on what I have seen of other junipers here I suspect you are likely to end up with a rather thin and dirty aspect at eye level, with or without shearing. Shearing will prevent it from opening up for some years, but eventually it will thin out even with that treatment.

Here is a link that might be useful: Monrovia - SPARTAN JUNIPER

Thanks everyone for your feedback. I'm totally new to growing conifers, so I appreciate all your input.

Resin, the narrow area is a planting strip between the curb and street and there is full day sun.

I didn't want a tree, because I don't want to shade out my front yard, its a small urban garden. I planted the juniper there, thinking it would slightly screen out the apartment across the street and give me some needed green, while providing a thin column of shade rather than a huge canopy, even though a tree would be the perfect screen, then I'd lose the sun in my front yard.

Marshall, the plant fits your description. Single stem is what I want to keep it at, but not if its an impractical idea.

The reason I thought it would be nice as a narrow tree because the planting strip is already crammed with roses and perrenials and I am partial to tree trunks and like how shrubs look trained as small trees, I just thought it would help the whole planting strip "breathe" a bit better, while giving it some backbone.

Bboy, I don't know what you mean by "rather thin and dirty aspect at eye level" Even if its a single tree trunk for 4 or 5 feet? I figure then I would never or only rarely shear it all the upper growth.

So, to grow it as a narrow tree, do I just keep it staked and gradually trim off lowest branches from the main stem as it grows?

Thanks again.