For a riot of colorful blooms all season long, plant annual flowers. They complete their life cycle in one season, which means they continue blooming until killed by frost. For even more flowers, remove the faded blossoms by "deadheading"--snipping off the faded blossoms. This encourages the plants to put their energy into producing flowers rather than seeds, which is what they'd do if the faded flowers were left on. Almost all annuals prefer full sun and they come in a variety of sizes, colors and flower shapes. Flowering annuals are ideal to tuck among perennials that bloom for only a short time. The annuals will provide a pop of color among the varied foliage of your perennial border.
Petunias are one of the most popular flowering annual. Their growth habit is varied, depending on the variety. Grandiflora petunias have the largest flowers and are predominantly upright plants. They develop into large mounds of flowers about 12- to 15-inches high. Multiflora petunias are more compact with smaller flowers in greater numbers than Grandiflora petunias. Most varieties are single petaled, but some double petaled varieties exist. Multiflora petunias are often planted in large blocks of a single color for a huge splash of color. Milliflora petunias produce copious numbers of tiny petunia flowers about an inch and a half across. The plants are compact and make excellent edging plants or additions to container gardens. Groundcover petunias grow only 6-inches high but spread rapidly to cover a large area. They often trail 2- to 3-feet over the edge of hanging baskets or window boxes.
African marigolds (Tagetes erecta) are the tallest variety of marigolds, with some varieties growing up to 3-feet high. They have large double flowers in orange, gold, yellow, cream or red. African marigolds make excellent cut flowers that last a long time. They are often one of the last annuals still blooming at season's end. French marigolds (Tagetes patula) are small bushy plants that grow from 6- to 18-inches high with 2-inch flowers that are single or double. Colors include yellow, orange, tangerine, scarlet, mahogany or bi-colored. Signet marigolds (Tagetes tenuifolia) are small bushy plants with lacy foliage that has the scent of lemons. Their flowers are single petaled in yellow, orange or rust. Signet marigold blossoms are edible and have a slight licorice taste similar to tarragon.
Cosmos are prolific flowering annuals that are easy to grow in the home garden. Most varieties fit into one of two types: Cosmos bipinnatus and Cosmos sulphureus. Cosmos bipinnatus are the tall, graceful cosmos that produce white, pink and dark rose flowers and the seeds are most often sold in mixes of these colors. This variety of cosmos grows up to 4-feet high and has lacy foliage that resembles ferns. Cosmos sulphureus has long narrow leaves with hairy margins and flowers in the warm color family of red, orange and yellow. Cosmos sulphureus produce plants that are much shorter than Cosmos bipinnatus, only growing about 24-inches high. All varieties of cosmos are prolific self-seeders, often coming up year after year in your garden. Remove faded blossoms or collect the ripened seeds yourself.