Remember if you plant all perennials generally it will look barren in the winter. Why don't you look into interspersing with flowering woody plants and although deciduous it will still leave some character in the winter against a snow backdrop. Spirea, potentilla, weigelia, etc.

Here is a link that might be useful: Propagating Perennials

As a landscape designer, I'd say that designing a perennial border for maximum color over the longest period of time is one of the harder tasks to achieve. Typically, it is a bit of a trial and error process over a period of a few years. Perennials, especially those planted in decent soil, often exceed growth expectations or tag info plus many will need to be divided on a fairly regular basis and some are just very aggressive in their growth habits and will want to hog the real estate. Spacing, particularly for maximum impact and fullness, is always a challenge and will need continual tweaking. The interspersing or blending together effect is generally achieved over time or by incorporating self-seeding perennials or those often referred to as 'binders' or weavers - sprawling type plants that tend to take advantage of their neighbors for support and that will weave through and tie various sections of the border together. A number of hardy geraniums fit this bill, also herbaceous clematis.

In addition to combining for flowering time, you need to pay attention to foliage effect. Some perennials offer great foliar attributes both before and after bloom period - others look terrible after blooming and will need to be cut back for aesthetics. And a border consisting solely of perennials is generally going to be bare ground a good portion of the year and is best addressed by including appropriately sized shrubs or dwarf conifers, etc. to provide some structure and provide winter interest. And don't forget to include evergreen groundcovers or perennials that retain their foliage all year - there's quite a few.

It may be worth looking at The Well-Designed Mixed Border by Tracy DiSabato Aust at the library or local bookstore. This will provide you with all sorts of pictorial inspiration as well as tips on how to combine perennials for maximum impact and year long color.

Gardengal, your post sent me straight to the library to look up that book. You're just a bit off with the title. It's actually: The well-designed mixed garden : building beds and borders with trees, shrubs, perennials, annuals, and bulbs
..unless she has another book that you are thinking of.

Just wanted to get that out there for folks using search engines or card catalogs. Thanks for the tip. I have her book on pruning and it's very helpful.