Borders can be one of the most difficult areas of garden design. They can be straight, curvy, narrow or wide or all of these together. I admit my choice is to have all of these characteristics in a border. For many years I had borders that hugged my home, straight up against the house going all the way around from back to front. My borders were beautiful but only during the month of July. I planted all summer flowering perennials because I did not know how to plan for all season interest,
What is wonderful about gardening is that you are always learning, changing, reinventing. Evergreens and dried grasses add winter interest, structures such as pergolas, arbors, tuteurs and seating are all part of keeping your attention in the colder climates.
Daylilies bloom throughout three seasons, roses bloom three seasons, Rozanne perennial geranium, Max Frei perennial geranium and on and on. Blubs of course are a staple for spring bloom and there are many fall blooming plants. Don't hesitate to put annuals in your border to keep it in continual bloom.
Highs, middles and lows are important in plant selection. Don't be afraid to put a very tall grouping next to a lower grouping, keep the wave going visually with plants, not just sculpting out the border. Use some weavers, those long viney plants that crawl throughout the border. Repeat plants, repeat colors, repeat viney, tall, short, etc. Oh, I could go on forever, but there is always another day to talk about specific plants.