If you want a natural ook do not plant plants in an evenly spaced row for starters. I see a very big evergreen very close to the house on the right that should actually be removed and is the area in the front of the pic your property? I honestly can’t see the need for anymore trees on your site and the space you use seems to already be very private.

That was my first thought also. Is additional privacy needed??. But this is coming from someone who lives on a very narrow lot in a very busy beach town with my patio to the front of my house.

Plenty of room between trees and the next house. There is a 15 foot wide swell and probably another 30 feet until you reach it. It is actually a shed and not their home. I’m on a 1.25 acre lot. The additional privacy would be more of a luxury as the rest of our views are open/trees, but this is the primary view.

How fast do you want this to fill in?

I second, "Do not plant [like] trees in an evenly spaced row," if you're seeking a "natural" look. It would make it much easier to achieve the so called natural look if you could move one of the existing trees. If we number them 1 through 4, beginning at the left, you could move number 4 to between number one and two. Bring it forward about 6' and then 2' to the left. Then you'd have an irregularly spaced row of plants to which you could fill in with other irregularly spaced groups of trees & shrubs, and maybe a couple of individuals. But work it all out on a piece of paper -- a PLAN -- before you make any physical changes.

Keep in mind that fast growing trees towering over evergreens that need full sun, are going to cause them to lose foliage. Create a plan that minimizes this by keeping some separation between these two categories of plants. Also, keep in mind that you have plenty of space and "natural" is 3 dimensional. You're going to want to have plants not in one row but maybe in the equivalent of 3 rows -- that are full of "holes." When they're seen in total they add up to solid screen. And shrubs would fill in some gaps so there is some smoothness to the bed line. You wouldn't want an irregular sawtooth end to your lawn, but a smooth one ... probably a long, gentle, slightly concave curve, such as ...

Where in zone 5? Do you have issues with deer? Do they all need to be evergreen, or are deciduous plants OK? As Yardvaark and PC said, having irregular spacing and more depth than a single flat line of plants will look more “natural”.

I would be looking at large shrubs, so if you are in an area with acid soil, consider some of the larger Rhododendrons that can range in size from10-15’+. Look at the “iron clads” and Rhododendron maximum.

If deciduous plants are OK, look at

larger red-twigged dogwoods such Cornus ‘Elegantissima’

bigger selections of Hydrangea paniculata such as Pink Diamond, PeeGee, or Fire and Ice

Ninebark/Physocarpus

large cultivars of some of the hardiest forsythia

To maximize growth rates, you want to allow your shrubs an area free of root competition from grass, so remove grass for a few feet to either side of the shrubs and mulch well. Work out a way to provide water for the first couple of seasons, especially during dry periods. If hoses don’t reach, consider filling trash cans or other lidded containers in he back of a pickup or on a garden cart that your riding mower can tow out there and siphon water out. I planted a large shrub border with mostly small plants in the fall of 2009, and within 4 growing seasons it had filled in well enough to give good blocking of sight lines where I wanted it. This thread has some photos taken during its first 4 growing season (half way down the thread) and with a mix of evergreen and deciduous it completely blocks sight lines in summer and mostly does so in winter even though it looked really sparse during its first season.

I’m on the IL/WI border. Hoses reach so water is no issues. I appreciate the suggestions I planned to dig out the grass and mulch.

Just remember that fast-growing shrubs also grow fast once mature--that is, they need trimming/shaping more often.

I haven’t found that all shrubs that start out fast continue that way once they approach the expected size from a reputable source such as the Missouri Botanical Garden. So for instance, both my Physocarpus ‘Coppertina’ and my various panicled hydrangeas started out life growing fairly fast, but don’t put on much growth annually by now at 9 years. I set original spacing for mature size, so I don’t need to prune to size, which may be what yvonnecmartin was referring to; pruned shrubs do regrow quickly. While mine were getting to size, I had large perennials in the spaces, and either moved the perennials out or let them get shaded out as the shrubs grew, but things did look a bit sparse for about two years.

Deer love to eat the new growth off my physocarpus. I sprayed them this year with deer repellent and they have more than doubled in size. Just be aware that they will need protection for a while until they have a lot of woody stems.

Red twig dogwood, forsythia bushes, lilacs, smoke bush. weigela, rose of sharon and pussy willow trees. Just a few that I have for privacy screening and are deer resistant. I am zone 6, so I don't know if all of them would grow in zone 5. People think forsythias need to be trimed, but they don't. They grow into a beautiful arching large bush. You just have to trim them a little the first couple years to promote bushier growth. Pussy willow you can't plant near water lines, septic tanks, etc. Rhododendrons grow large, but takes a long long time.