They will not bother each other in the least. The Periwinkle might grow up into the lowest branches of the conifers but it doesn't really matter. However, I would urge you to make sure you have got all the Canada thistle and what looks like Goutweed out of the bed before planting anything new there. And that might be difficult while the Periwinkle is there since it will involve either thorough digging or some kind of herbicide, if you are not averse to them.

I would prefer to do it natural but the ground is covered in plants I don’t necessarily want so I may have to do it the quick way.

It will take several years to be sure all the goutweed is gone. Also, Green Giants will get very wide--20 feet eventually--and up to 50 or 60 ft tall. Is that really what you want?

lets be a bit more precise with the above comment.. YOU DO NOT HAVE THE SPACE FOR GREEN GIANTS ... period

as to the vinca.. its basically a surface plant.. and will grow just about anywhere you want it.. even in full shade ... and if you dont like where it is..move it easily.. in a cool season is best ...

ken

" even in full shade "

That's exactly where it is supposed to be!!

And you can keep the Green Giants quite narrow by hedging them. But if you don't care for that sort of maintenance, then perhaps select a narrower, more columnar arb like Smaragd or American Pillar.

We have a two story home and an apartment building to cover behind our house. Also a talllll pine tree in the corner of our backyard. We want an Arb that’s gonna cover that building completely and match the height of the one tree. We will keep them maintained over time

You have access to a cherry picker?

That isn't a rhetorical question. Many years ago we were on a garden tour in Maine. One of the gardens had a carefully pruned, perfectly cylindrical white pine - up to about 15 ft. Above that, it had gone wild. It was an interesting, and memorable effect, the drove home the idea that it isn't at all easy to prune trees once they get above stepladder height.

I appreciate everyone’s concern, I didn’t ask for people to question my yard size which you all aren’t even sure what my backyard looks like. I have Apartments staring down into my backyard and I want that covered up. No one on here is paying for the maintenance of my trees so I’d appreciate if you’d keep the suggestions along the lines of what I asked for 👍🏽

I don’t know how you prune/ shear an arb into narrower shape when it’s 20’ tall and half is next to fence.

If you’re trying to “ obliterate “ any sight of a 2- -story or apartment building roofline, that’s a “ tall” order.
But for their view into your yard, you may be able to use something considerably shorter. Depends on the sightline angle. Also not understanding blocking view of a pine tree.

You do it before it gets that large!! I am not sure why this is such a dilemma to so many. It is a very common practice here with both GG's and Leyland cypress. It is just not that big a deal.

Thank you! @gardengal I need a fast growing Arb and have done more than enough research, I know what my house can handle. I asked about Periwinkle roots and not why I’m choosing a tall fast growing Arb. Their comments aren’t changing anything

I may have misunderstood. I get the idea of pruning early. But, I initially thought the OP wants a 20-25 ‘ or more height as a goal. But perhaps just wants the shrub to reach a lower height, but faster.

Sounds like you’ve got all the information you want, though.

. One of the gardens had a carefully pruned, perfectly cylindrical white pine - up to about 15 ft. Above that, it had gone wild.

==>> that was the front corner of dads house... and it was one of my jobs to keep it sheared for 20 odds years... it was a god forsaken job.. i was covered in pine tar by the end of the day ...

suspiciously...he had it removed.. about 5 years after i moved out.. lol .. it had doubled in height.. and was about 15 feet taller than the house...

ken