Flowers bloom to set seed. Annuals bloom prolifically throughout their growing season and then die back. Cool season annuals like pansies, snapdragons and stock stop blooming when the summer heat hits. Warm season flowers like cosmos and marigolds bloom until frost. There are many flowers from bulbs, bushes and trees that bloom only once a year rather than all season long like annuals.
Spring bulbs like tulips, daffodils, freesias and crocus bloom once in spring. Summer bulbs and corms such as bearded iris, gladiolus, Asiatic lilies, oriental lilies and amaryllis bloom once during the summer. After blooming, the leaves continue to grow providing energy to the bulb so it can re-bloom the next year. Cutting back the leaves won't necessarily kill the plant, but it will significantly decrease the amount of flowers the following year.
Wild roses bloom once in late spring. The bushes are literally covered with thousands of scented single rose flowers in shades of pink and white. Modern roses have been bred to bloom continuously throughout the warm months. There are varieties that bloom only once but gloriously. They include banshee, fruhlingsgold, alba suaveolens, complicata, and Paul's himalayan musk. Lady Bank's is a climbing rose that has either yellow or white tiny flowers that blooms in early summer.
Spireas, sometimes call the bride's bouquet because of the masses of white flowers, blooms in the spring. Forsythias are covered with yellow tubular flowers in early spring before leaves appear. Lilacs are a cross between a vine and a bush. They need a strong support because the branches can get heavy. They bloom in shades of lilac, of course, but also pink and white with heavily scented flowers. Azalea blooms in vivid shades of pink, purple and yellow as well as white. It prefers semi-shade.
Dogwood flowers bloom in pinks and white. The petals are notched with a darker color. Crabapples for making jelly don't have particularly attractive flowers, but ornamental crabapples, such as golden hornet, have masses of pink buds that open to white flowers with a bonus of golden fruits in the fall. Witch hazel, growing to 12 feet, has curled narrow petals blooming in very early spring. The petals uncurl during warmer sunny weather and retract during cold weather. Hawthorn, a tree that grows to 25 feet, has deep pink flowers.