Amid the confusing jumble of seed packets and nursery pots, it's often hard to keep track of what categories certain flowering plants fall into. It's important for bloom-lovers to remember that many shrubs, trees, aquatic plants, vegetables and herbs produce flowers, usually to increase their fruit yield or otherwise perpetuate their own pollination. But plants whose main purpose is to produce a bloom fall into three key categories.
Unlike perennials or bulbs, no part of the annual flower remains underground to rebloom the following year. Annuals must be bought anew, or grown from seed, each year. The good news is that using annuals in at least some of your garden beds enables you to experiment with new color and height schemes without the bother of digging up established plants. Garden writer Barbara Damrosch notes that annuals are easier to grow from seed than perennials, have longer bloom times and suffer from fewer pests and diseases than perennial flowers.
Flowering annual species include the hardy types--those which can be planted before the last frost date and survive, or even prosper into the fall. Hardy annuals include calendula and bachelor button. "Half-hardy" varieties, such as petunias and cosmos, can survive a few frosty nights but succumb more quickly to cold weather than hardy annuals. Wait until all danger of frost passes before planting members of the biggest annual group, warm weather annuals. Zinnias, impatiens, stock, nasturtiums, portulacas and verbena fall into this last sub-category.
Even after their blooms fade and their stems wither, the roots of perennial flowers remain, waiting for another year to spring from the ground. Whether you grow perennials from seed or purchase them as seedlings, put thought into where you will place them in the garden, because perennial beds are much more permanent than annuals ones. As a group, perennials tend to have shorter blooming times than annuals, making perennial bed planting a bit of a challenge. Some gardeners interplant early, mid and late-season perennial flowers so that something is always in bloom, while others just plant their favorites, sometimes filling colorless patches with annuals.
Early-blooming perennials include iris, blue phlox, bellflowers, pinks, poppies and gas plants. For perennial flowers that burst into bloom at the height of summer, plant bee balm, coreopsis, Shasta daisies, sundrops, veronicas and day lilies. Fall classics include the perennial flowers autumn monkshood, sedum 'Autumn Joy,' chrysanthemums and purple asters.
Of course many flowers straddle the line; "biennals" like foxgloves are simply perennials that achieve full bloom every second year. Others, like chrysanthemums, are "tender perennials," meaning that they can't handle extreme weather and should be treated as annuals in certain climates. Even some annuals self-seed so freely that they're considered de-facto perennials. Alyssum, nasturtiums and calendula fall into this group.
Technically perennial flowers because they return year after year, bulb plants tend to be mentioned separately because they grow not from a fibrous root system, but from a tissue mass that looks like--well, a bulb. Many bulbs need to be planted in the autumn, making them one of the few fall chores that involve planning something new, rather than cleaning up the depressing debris of the past season. Nonetheless, the terms "spring bulbs," "summer bulbs" and "autumn bulbs" refer to bloom times, rather than planting times. Your nursery will tell you the optimum planting times for each type.
Spring bulbs are often the first flowers of all to emerge each year, sometimes right through they snow. This group includes most crocuses, winter aconites, anemones, scillas, daffodils, tulips, snowdrops and glory-of-the-snow. For bulbs that glorify summer gardens, establish tuberous begonias, dahlias, most alliums and lilies. The smallest group, fall-blooming bulbs, includes autumn crocus and the alliums A. stellatum or A. thumbegii.