I'd plant now for sure but you'd do well to pay particular attention to watering deeply from planting until your ground is frozen.

Most of the many Thuja establishment issues I see around here ALL relate to their not being watered deeply enough to actually penetrate the root mass. This requires a hose on a slow trickle and a dig down or two to understand how your own soil percolates and moves water.

If you can do that then planting now is ideal.

Do mulch well and don't amend the planting hole.

i agree.. the biggest problem will be watering deeply on a hill ... you have to insure it doesnt move downhill before it soaks in ...

otherwise .... now is the time ...

you dont mention size .. but if rather smallish ... you can block winter wind with a simple burlap wind block.. as compared to wrapping them or whatnot ...

smaller transplants get established faster.. and usually outgrow large transplant in a 3 to 5 year period

do keep in mind.. real winter doesnt start .... until about mid january... usually... so you have upwards of 3 to 4 months for the plants to settle in ... just because you are cold.. doesnt mean a zone appropriate plant THINKS its cold out there ...

ken

Ok, so it sounds like September could work.

I've attached a couple pics to illustrate what I'm trying to do. Feel free to let me know if my selections are not good or there's better options. I have what was an overgrown clump redbud that came with the property, probably about 20 years old. I've been pruning in stages for the past 3 years, to get it back into decent form and raise the canopy. It's lost a couple trunks due to it's weight and bearing the brunt of summer storms coming from the west. I'd like to keep it...they grow native everywhere here and it's a stunner in the spring. They look good, in my opinion, flanked by larger evergreen or deciduous trees. This one looks a little ragged come late summer, and I thought about starting to give it some protection. I'm considering starting with either Norway spruce or Thujas on each side of it, about 15-20 ft away, knowing they'll eventually dwarf the tree yet give me that natural setting look. The redbud is about 25 ft from the edge of the road for reference. I'm the first house into the neighborhood entrance, so getting some evergreen conifers going here would add a lot of privacy to my yard. Any other ideas are welcome.