What narrow 15 foot+ tall evergreen plants grow in USDA Zone 6b?

Question

I'm in USDA zone 6b bordering on 6a in Ohio.

I've looked at lines of sight for my house and concluded that a few privacy plants would be good, if possible.

Some of the new plants should be narrow or able to be trimmed that way. I would plant them near a neighbor's driveway (hopefully with their permission, but not strictly required). I don't want plants spilling into their driveway, or to need to trim them constantly to avoid that. I also am looking for low maintenance or medium maintenence.

I'm looking for plants that are about 3-5 feet wide to block my window view of my neighbor, but not so wide that it takes up the whole side yard. This would be for a second floor window so it would ideally be 20 feet tall. "Columnar" or "Fastigiate" seems to be an attribute to look for.

I guess I'm looking for it to reach 15 feet within 10 years.

I asked some AI assistants and they told me:

1. arborvita
2. boxwood
3. Holly
4. blue arrow juniper (a bit narrow at 2 feet)
5. Hetzi Columnar Juniper

My backyard will have green giant arborvitas because there's no space concern.

Seeds and whatnot are another thought. If I'm covering my neighbor's car with seeds that's another thing to consider.

East yard:

The east yard has the tightest space concern, about 9 feet from the heat pump to my neighbor's driveway. And the first 3 feet are not mine. Heat pumps are like AC; you want to keep the area around the fan clear for maximum efficiency. 11 feet from driveway to the left side outcropping with the window I'm blocking.

Sun is decent in the east. 20-30 feet between the houses, and a lot of tall trees in the area, but still pretty sunny.

There would be probably one plant at A, B, or C; and another narrow plant at D.

West has enough space where it's not a big issue. Similar sun conditions.

F, G, H would all probably be their own narrow plant. Or put one plant at the midpoint of F and G.

H is towards the front of the driveway so narrowness (maybe 6 foot max, ideally ~4 feet) is a larger concern.

TLDR: I want a 15 foot+ tall evergreen plant that is 4 ft wide.

Answer 1

Note that I am an amateur and have no plant experience. However, based on my research, these plants are evergreen, narrow, and would grow in USDA zone 6b.

See the comments to the OP question for some important points on other factors that influence growth (spacing, drainage, etc.). Also pay attention to whether any of the species are invasive in your area. Holly for example is probably invasive on the US west coast.

For the height and width, I generally took the most conservative estimate for mature height/width I could find. For sun, I went with consensus, but it seems there is some debate. It also does not appear to be consistent what happens when a plant gets less sun than it's supposed to - some die, others grow more slowly, others change color.

Some plants listed are below the 15 foot limit but might grow that high depending on who you ask, and the conditions.

There is an almost limitless amount of cultivars for some of these plants. Even after 20 hours of research I was finding new ones. If there's a plant that almost meets your needs in one dimension, try seeing if it has a cultivar that may help in the other dimension.

Larger plants may be able to be trimmed to meet these specifications. However, it seems that the less the plant meets the height/width you're going for, the more trimming you will need to do. And trimming can kill or hinder a plant, depending on how receptive it is to trimming.

Finally, it appears that some plants have little to no upper limit on height (or width?). See for example this alleged Juniperus virginiana var. virginiana 'Canaertii' that is easily 50 feet tall and decades(?) old.

name	sun	height (conservative)	width (conservative)
American Pillar arborvita (Thuja occidentalis 'American Pillar')	unknown	15	3
Colorado Blue Spruce (Picea pungens ‘Fastigiata’)	full sun	20	10
Moonglow Juniper	full sun	20	8
Colorado Spruce ‘Koster’ cultivar	full sun	15	5
skyrocket Eastern red cedar Juniperus virginiana 'Skyrocket'	full sun	15	3
white spruce	full sun	12	5
spartan juniper	full sun	15	4
taylor red cedar Juniperus virginiana 'Taylor'	full sun	15	3
red cedar brodie Juniperus virginiana ‘Brodie’	partial sun	15	12
dragon lady holly (may be invasive and have aggressive roots)	partial sun	20	5
malonya thuja Arborvitae Thuja occidentalis	partial sun	20	4
baby blue spruce Picea pungens 'Baby Blue'	partial sun	15	10
Leyland cypress (with pruning)	partial sun	60	20
sky pencil Ilex crenata 'Sky Pencil'	partial shade	6	2
eastern red cedar (many varieties including taylor and brodie)	depends on cultivar	depends on cultivar	depends on cultivar

Further reading

https://www.thetreecenter.com/eastern-red-cedar-the-toughest-juniper-there-is/

https://leafyplace.com/narrow-evergreen-trees/