A variety of both annuals (plants that survive for one season) and perennials (plants that return year after year) drop seeds into the ground that may sprout and grow new plants the following year. This is known as self-seeding, and it can save you money on next year's gardening.
Cosmos, native to South America, is named for its perfectly spaced flower petals that reminded early cultivators of the harmony of the universe. The most common color of cosmos is yellow, though other colors such as red, white, pink and orange are available. This annual is easy to grow and can become quite tall, producing numerous blooms if grown in full sun. Collect seeds from the plant after flower petals drop or allow cosmos to scatter its own seeds naturally.
The black-eyed Susan is a late-summer garden favorite. The tall stalks produce yellow to orange daisylike blooms with a dark brown to black center. This North American native perennial is sometimes considered a weed because of its prolific self-seeding. Seeds may be scattered by wind or by birds into nearby flower beds. Black-eyed Susans will survive some shade, but they thrive where they receive six to eight hours of sunlight a day.
Sweet alyssum is known and named for its strong sweet scent. The flowers are small and white, making an excellent ground cover. This low-growing annual spreads rapidly and self-seeds; thus, it is a low-maintenance backdrop for taller, more showy plants. Place alyssum in front of tall lanky flowers such as black-eyed Susans, foxglove and echinacea. Plant in full sun or partial shade. Shake seed heads from spent flowers over any areas in which you want to see more alyssum.
Violas, or Johnny-jump-ups as they are commonly called, are prolific self-seeding perennials with small violet and yellow blooms. The stems are thin and fragile, and the leaves are divided and said to resemble bird's feet. This flower will spread easily throughout the garden, providing a fragile but full ground cover. Plant smaller flowers such as violas in front of taller plants or use violas as a garden border. These petunialike blooms prefer sunny locations.
Petunias bloom in a variety of colors, including pink, red, white, purple and combination blooms. These colorful blooms have the distinction of being one rounded petal. These annuals will self-seed in containers and in the garden. They make colorful hanging baskets as well as backdrop garden plants. Most varieties of petunias require six to eight hours of sunlight a day for optimum growth.