I was hoping for advice from those with zone 4a tree knowledge. Our new home is placed on a relatively narrow city-style lot in a new neighborhood. The lot next door is unbuilt now, but we'd like to get a head start on creating a privacy screen. We'd like some privacy from our future, yet unbuilt neighbor's windows in addition to something green to look at in winter. We live in a homeowners association where trellises and tall fences are not an easy option. I'm interested in recommendations for trees or tall shrubs for use as a natural privacy screen instead. I've seen some info about Emerald Arborvitaes and Irish Junipers in Minnesota- but I've also seen lots of conflicting mature size specifications on those plants.

In order of importance I would like:

1.) A hardy tree or trees, forming a small informal line group, rather than a formal line of columnar trees. to form a narrow year-round privacy screen

2.) Possibly columnar in form, no less than 10 feet tall, but hopefully around 12-25 feet tall.

3.) Trees that don't require much pruning. I'd rather have a natural-looking screen, rather than a formal, manicured/sheared hedge.

4.) Something that won't take forever to grow to the desired height

5.) Hopefully more than 1 variety of tree - possibly a few complimentary varieties in the grouping?

6.) Something that I can find locally at a garden center or good landscaping store.

7.) It may be too much to ask, but we really like the Japanese/informal garden styles of design.

The area I'd like to place the screen is:

1.) Zone 4a Minnesota - Northern Washington County

2.) A screen that's roughly 12 feet wide, blocking the views of windows of the 2 houses.

3.) There will be only about 15 feet between the houses, and only 6 feet to the lot line, so I'd like something upright & narrow.

4.) The area is sloped from north at the top to south on the lower side of the hill.

5.) I think the area would be considered full-sun as there is nothing blocking the southern sky and not much to the east or west.

6.) Soil is somewhat clay.

Does anyone have any experience they could share? Any recommendations? Thanks very much for your considered opinions.