When you decide to start a flower garden, you know you want non-stop color, fragrance, and easy care. You want it to be inviting to butterflies, honey bees, and birds. You want to bring pleasure to visitors, the neighbors passing by, and of course, yourself!
But what types of plants to use? When people talk about plants, you might have heard the terms annual, biennial, and perennial. These terms describe a plant’s life cycle – how long they live and when they die.
All plants have a life cycle. Some only live for one season – growing, flowering, and setting seed in just a few months. Others live for decades – the foliage dies back and they sleep under the snow waiting to bloom again. And there are still others that give you leaves the first year and flowers the second year before they die.
All plants, from trees and shrubs, to flowers, herbs and vegetables, to grasses, lawns, and groundcovers, are one of these three.
The term can often be confusing. We usually think of “annual” as meaning “every year.” But for plants, it means how long they live: one year.
True annuals complete their life cycle in one growing season. They sprout from seed, grow roots and leaves, produce flowers, and then develop seeds for the next generation. After that, their job is done and they die. They can be summer annuals, whose seeds sprout in the spring, or winter annuals, which start their growing season late in the fall. But they all complete their life cycle within one year.
Popular annuals include petunias, marigolds, zinnias, and snapdragons.
Some gardeners might wonder if annuals are worth planting since they have to be replanted every year. The answer is yes! If you want continuous flowering all summer long, annuals will provide that.
Because annuals grow, bloom, and die in one season, they flower prolifically all season long to produce as many seeds as they possibly can. The design that you create stays the same all summer long. Deadheading (removing the spent flowers) and fertilizing keep them blooming for months. They are great to use in container gardens, flower beds, and hanging baskets. Victorians adored annuals and spent a lot of time and money designing highly stylized flower gardens in a process called “bedding out.”
Some annuals, like verbena bonariensis reseed so freely you might start thinking of them as perennials.
Tender and Half-Hardy
You may have heard these terms in reference to perennials. Some plants grown as annuals in places with cold winters are perennial in their native habitat. They can be tender or half-hardy, depending on where you live.
Think of this as a spectrum- plants that are hardy perennials in USDA zone 10 may be tender perennials in zone 9 and half-hardy perennials in zone 8. Or hardy in zone 8, tender in zone 7, and half-hardy in zone 6.
Tender perennials cannot take any bit of frost and sometimes don’t even like temps below 50°F (10°C). Impatiens, begonias, cannas, tropical hibiscus, and tropical “house plants” like crotons are considered tender perennials. They are sold as annuals in colder zones.
Half-hardy perennials are those that can withstand some cold weather and even a few light frosts. Geraniums (pelargoniums), dahlias, lantana, coleus, and tropical hibiscus are considered half-hardy and are also sold as annuals further north.
Perennial plants live for three or more years. They die back to the ground each autumn, but their roots live on and they sprout up again the next spring. Perennials can be divided into two categories: herbaceous and woody. Herbaceous plants die back to the ground each year – no sign of them remains through the winter. Woody perennials retain their stems and branches.
Popular perennials include roses, hosta, heuchera, monarda, daylilies, black-eyed susan, coreopsis, lavender, and ornamental grasses.
Each type of perennial blooms within a certain time frame. Peonies, for example, bloom for about 2 to 3 weeks at the end of May in the midwest. Coneflowers have a longer bloom time, up to 3 months, longer if you keep deadheading. Some bloom early in the season like iberis and bleeding hearts, some bloom in the heat of the summer like balloon flowers and shasta daisies, and some don’t start flowering until autumn arrives, like asters and anemones.
Tips for Growing Perennials
Designing a garden with perennial plants can be tricky. You need to consider size, shape, texture, and flower color, and you also need to consider bloom time. A garden of perennial flowers is ever-changing, what with staggered bloom times and all the digging and rearranging we do to get the garden “just right!”
Biennial plants complete their life cycle in 2 growing seasons. The first year they produce roots and vegetative growth. The second year they flower, set seed, and die. Popular biennials grown for their flowers include foxglove, forget-me-not, canterbury bells, hollyhocks, and sweet william.
Several vegetables we grow annually are actually biennials grown for their leaves and roots – beets, onions, parsley, carrots, and swiss chard, to name a few.
And some of the most infamous weeds are biennial – garlic mustard and burdock!
Tips for Growing Biennials
Biennial plants are hard to find in nurseries and garden centers, so starting them from seed is best. If you sow seeds every year, you will always have some plants in flower and some in their vegetative stage. Many of these will reseed freely and pop up in unanticipated places. If you want a true cottage garden look, biennials will add a lot of charm.
What’s Right for My Garden? Annuals vs. Perennials
Planting with annuals is temporary, but perennials are more-or-less permanent.
Use annual flowers when you want a big burst of consistent color all summer long. Use them to fill in bare spots, get a jump on the season, or extend it with flowers like pansies, kale, and nemesia. Use them in containers and hanging baskets. If your budget allows, it’s fun to change them out – pansies and osteospermum in the spring, calibrachoa and petunias in summer, and mums and kale to finish out the year.
Choose perennials for the structure and stability of their foliage, the flowers as secondary. Choose these plants for their ebb and flow as the growing season progresses. Using iconic spring, summer, and fall bloomers gives your garden a sense of time. Native plants will invite pollinators when they need the nectar of the flowers most.
Mix them both – one is not “better” than the other! And then add a few biennials to remind you of your grandmother’s garden.