Perennials v. Annuals v. Biennials
I'm often asked, usually with some embarrassment, the difference between annuals and perennials. I think what makes it confusing is that "annual" when referring to appointments means to happen yearly. Just like an appointment where you need to make a call to your doctors, taxman, and mechanics these annually occurring appointments need to be initiated by you just as annuals need to be seeded or planted as starts every year if you want them to appear. Examples of annuals: cosmos, calendula, certain varieties of salvia, and petunias.
Perennials, when planted for your correct growing zone, will come back year to year. The word "perennial" has Latin roots in the word "perennis" meaning, lasting through the years. Examples of perennials: Veronica, Shasta daisies, ajuga, and bee balm.
Then we have the biennial. A plant that lives for two years. It's first season the plants develops roots and pushes forth foliage. The plant gains the energy for next year's push to flower and seed. Examples are mulleins, forget me nots, foxglove, hollyhocks, dame's rocket,and sweet william. It's important that if you want these plants to return through their own volition you need to let them seed themselves. Do not deadhead them unless you want to rely on nursery stock to fill there spots after the second year.
We then start to play with "soft" perennials that may survive conditions in a zone warmer than where you live. I live in Jackson, WY. The perennials I select need to be able to survive a low of -40 degrees. My growing zone is 4. I have micro climates within my garden created by walls, trees, and shrubs that create areas that are warmer by radiant heat or the blocking of cold winds. I have some success at growing zone 5 plants. I also nurture these conditions in the winter by piling up snow in these areas to insulate the roots. The less melting and freezing of the roots the more likely they are to survive. The snow acts like a blanket and holds in the radiant warmth of the ground.
I also want to mention that when considering fruiting trees and shrubs such as, apples, cherries, and blueberries you will need to go down a zone to actually get fruit. So, if I plant a zone 4 cherry tree I may not get fruit but my tree will continue to grow and leaf out through the years. If I plant a zone 3 apple I have a much greater chance of being able to harvest a copious crop of fruit. I fantasize all summer about picking my sour cherries and making sauces, pies, and jam. My apples are usually devoured by my daughter who has a hard time waiting for them to ripen.