An 80' hedge of one thing is going to give a little bit of a formal feel. Is that what you want? If you plant in staggered rows, it will seem a LITTLE less formal, but won't entirely diminish the effect. A problem often comes in when you need tall evergreen material, because there are fewer choices that will be suitable for any given climate...

Personally, if I only needed a 6' hedge, was okay with some of the material being deciduous, and was into flower color- I would definitely mix it up, though!

Also, trying to line up a huge quantity of your one ideal though may prove very, very tough.

Also, if you chose the one WRONG thing the results could be disasterous. And your hedge will be more susceptible to pest and disease manifestation.

SO, as a rule- diversity rules!

Snow Queen may fall short for you in height. Imagine the ease of replacing 1 versus replacing dozens and dozens of you are unhappy with the end result.

I planted a hedge row a bunch of years ago about 70-80 feet long. It has several different types of plants. It is also about 15-20 feet deep, which lets me have several rows of shrubs. That way no single plant has to provide 4 seasons of interest or work.

The backbone (nearest the street and sidewalk) is a row of skip cherry laurels. Next to them nearer the house, I have groups (drifts) of white flowering Diana (sterile) rose of sharon, leatherleaf viburnum, curly willow, japanese aucuba and a very large bridalwreath spirea in an irregular meandering kind of row that varys by the size of the plant. While the list seems long, over 80 feet it means that I can have have several of each species providing substance. The cherry laurels provide overall continuity so it doesn't seem like a mishmosh.

In front of these I have shorter shrubs and subshrubs, like polyantha roses the fairy, small hydrangea, nandina, euonymous, japanese maples. Depending on the areas, the whole thing is underplanted with pachysandra, coral bells, hosta, daylily, daffodils and other tough perennials. The small shrubs and the perennials provide the summer color. Repeating the same variety of hosta and coral bells also helps with the continuity.

(The rose of sharon is great, but I cut them back to 5 feet every spring or two otherwise they get too high. Same thing with the leatherleaf viburnum. The rose of sharon is worth it. The leatherleaf is in dispute: my wife loves it for background for photos. You might be too cold for aucuba. My snow queen is 4 feet after 5 years, but it is in shade.)

This enterprise is large and took a lot of effort, plants and money. But not all at once: It started with a double line of small $10 each shrubs bought at a clearance sale. But now, 10 years later, rather than simply being a privacy barrier, it is one of the features of my garden. People have begun to congratulate me on the park like conditions I have created.

With 6 hours of sun, you could have a fabulous park of your own. Not quite the advice you were seeking, but just a perspective.

Mix it up! I have a couple of 70+' work-in-progress mixed shrub borders that range in width from 6' to 20'. They are planted w/a variety of small trees, shrubs, conifers, ornamental grasses, perennials & vines. Some shrubs I have planted, all hardy to zone 5, are viburnum (trilobum, lantana, rhytidophylloides, ryhtidophyllum), aronia arbutifolia 'brilliantissima', serviceberry 'Autumn Brilliance', physocarpus (diabolo ninebark), sambucus 'sutherland gold', callicarpa 'early amethyst', hamamelis 'arnold promise' & 'diane', heptacodium, salix purpurea nana, cornus sericea (redtwig dogwood). To keep your border from looking like a mish-mash repeat some selections along the way. Good luck!

philipw2, your border sounds lovely!

With such a length, having a variety of bushes would certainly expand your period of visual interest. The layering of smaller to taller bushes sounds very good to add for more variety in blooms and color. I would always go for more variety over only one kind of planting. Gives me lots to look at all the time. Do consider the shrubs, bushes with good fall color, attractive bark, pretty berries for birds in winter.

May I suggest that instead of planting in straight rows of traditional hedge, that you make a scalloped or wave shaped front line of bushes. You could put taller evergreen bushes in behind the points of scallops, with smaller bushes in front of evergreens. Then plant the taller bushes you choose with heights rising from pointed area to curving back of scallop in between evergreens. Evergreens, columnar cypress for example, would be the same all year, pull the whole long line together in all seasons. Such a bending front line would give you a lot of footage for bushes, allow planting of smaller plants, perhaps a series of beds, alike or varied, in front of the taller bushes in rounded part of scallop.

Beds to fill in the scallops in front of bushes, could be annuals, solid perennials of the same type, theme flower beds each of a single color. Maybe a bench or statue, ornament, large pots of plants, centered in the scallops on lawn. Many ideas you could do. Hope this is helpful, give you some more ideas to go with.

I think a lot depends on what you are trying to achieve also. Some ambiguity with the term "border hedge". Don't know if their are clear cut definitions for either, but generally when I think of a "hedge" I think of a planting to either screen out an unpleasant view, mark a boundary, or create a windbreak or some such utilitarian function as that. A "border" connotes some type of significant feature unto itself. That's not to say a hedge has to be or even should be unattractive, but the emphasis is on function.
If you are trying to to create a real eye catching pleaser, I would again say- mix it up for maximum year round interest. If you are merely trying to create a sense of coziness or block out an unpleasant view- something simpler might be nice. If there is anything unattractive to be seen above the hedge line, consider that the busier it is the more your eye will be drawn to that area. Also, consider whether there are other focal points or beds in your yard that you might be distracting attention away from unintentionally. A uniform planting will draw the eye up and down its length but allow it to wander in other directions more easily. A mixed planting will more rigidly fix the eye and call other things in the same general direction into view.
Another factor is the distance from which it will be seen. A mix of plants that might be interpreted as a "mish mash" when seen from 60 feet away, will work just fine in a narrow corridor of space between two houses where only a couple of plants can be seen from any given angle at a time anyway. And if I'm standing or walking right next to a 6 ft border I'm more likely to focus on the hedge and not the eye soar behind it than if I am viewing it from a distance.
Others may have different design philosophies, but hope that helps.
I suppose you might combine both feature AND function into something that might VERY aptly be called a "border-hedge" and if that is the intention, just make sure that your function is met consistently across. For instance, if its privacy or traffic deterrence, make sure everything is sufficiently twiggy or dense to accomplish that. If you want to say "this is the edge of my property", a mixed planting can do it, but a single species planting might say it more loudly and clearly, particularly when viewed from afar. In the case of a true "border-hedge" that will be seen from afar, the aforementioned unifying plant (like the Cherry Laurels) is an excellent suggestion for cohesion. Though it doesn't necessarily have to be arranged in such a way that might be discribed as a hedge behind a border. You could "weave" a low growing unifier thru the entire length of the planting in a varety of patterns (more or less formal) as desired. I believe unifying the planting in this way would give you much greater freedom to be less repetitive (if at all) with the rest of the plant material- however you will want to strike a balance thru foliage colors and shapes,...

Marketingman I think we are both looking at a similar length and purpose. How deep are you planning?

I agree with the other posters - mix it up! In my case it's a question of how to mix it up with drought hardy plants, a who goes where.I'm planning a shrub bed around 15 ft deep.

Philipw2 do you have any pictures?

Lots of great ideas already, I don't know if I can add anything really useful, but here goes.

I agree about using different plants to expand the seasons of interest, but you can add some structure and rhythm by repeating one plant or grouping of plants over the whole length of the border. IE if your border includes sunny and shadier areas, you might repeat a single variety of something that isn't fussy about exposure, maybe a conifer, and then fill in different areas with different plants depending on the amount of sun in each area. Repeating a combination of plants is even better.

I have a long border that's backed along its entire length with spruce - too tall for you but the same principle. In front of the spruce are repeating areas of euonymous Manhattan (no, not the invasive burning bush euonymous, the evergreen kind), tree peony, and hydrangea (ranging from the tall Tardiva through medium height oaklaf and including some shorter mopheads) and the whole thing is underplanted with spring bulbs, hellebores, ligularia dentata and lady's mantle. I try not to plunk in random perennials, because I don't want it to look too busy - a constant temptation because I'm a plantaholic.

I'd try to avoid having more than a couple of "one of a kind" plants, while including enough variety to maintian interest all year; repetition really helps with that.

Okay, I don't believe there are any hard and fast rules with gardening, but one thing I (that's I!) find particularly annoying are hedges of two species of a very comparable size and shape alternating in a strict A-B-A-B-A-B-A-B fashion down a straight line.

diggingthedirt makes an excellent point about the unifier being non-fussy. I had that in mind when I used the cherry laurel in my example of a single plant being woven throughout. Unfortunately, they are probably not going to work in your zone. I think the right boxwood might work, though. Obviously boxwoods OR cherry laurels wouldnt be the standouts of a garden border, but when they might be so very important to the overall cohesion its almost better to consider them first. With any plant you hope to repeat in your design you have to consider sun exposure. If you don't have equivalent sun exposure, you will have varying results. You might expect uniformity, but you might have the sun plant being dense and full and the shade one being sprawly. If you have a lot of variances, this is generally an excellent argument AGAINST a uniform species planting. Exceptions might be the very versatile plants that are also tolerant of pruning so that you can correct for growth irregularities.

My three year old diabolo ninebark hedge (12 shrubs about 5' tall) provides a much needed summer screen. Last year they developed a wicked white, black and gray fungus that spread like wildfire threough the hedge. I pruned back hard to "improve air circulation" as advised by professionals I consulted...ALL OF WHOM were shocked that I would have ANY trouble with these plants! They decided it was an airborne, non preventable thing - and they'd come back fine in '06. Well, spring has sprung...and they look awful. They have few buds ..most look partially dead, but the top crown growth lookes good and healthy. What can I do to save them?

lovelyyard: you might consider posting your question as a separate thread, it would probably get more attention.
... I have no idea how to answer you, by the way ; )