Flowers for potting should grow in a mound or trail over the edge of the container, as this makes for a showy display, but they should not be flowers that grow on rhizomes or easily become root-bound, or you will have to transplant them every year into a larger pot. For these reasons, most gardeners choose colorful, long-blooming annuals for container planting. The flowers should also be small and hardy, as potted plants can quickly run out of room, nutrients and water.
Pansies come in a wide variety of colors, shapes and sizes. They are very hardy, fast-growing, and easily germinate from seed. Pansies will spread in a container and quickly fill it with bright, colorful blooms that will last all summer long and well into fall. In fact, many varieties of pansies will bloom all winter long, even after a frost, as long as you place the container in a sunny, sheltered location.
Alyssum, with its soft, delicate flowers and trailing habit, is the perfect flower for the edges of pots. The plant will quickly grow out and over the edges of the container, and the plant's white flowers (alyssum flowers can also be pink) will contrast nicely with whatever other type of plant you choose to place in the pot.
Iceland Poppies are a terrific complement to pansies. Similar in color and shape, they grow on tall stalks (up to 2 feet) and make a dramatic visual statement when placed in the center of a container and surrounded by shorter pansies. Like pansies, they thrive in full sun and prefer moist, well-drained soil.
Tulip bulbs can be planted in containers in the fall and then left alone outdoors through the winter. In the spring, they will reward you with graceful, colorful flowers on tall stalks. When the foliage dies down in the summer, fall-blooming flowers, such as mums, can be planted over them. Other bulb flowers are also great for pots, including daffodils and fragrant hyacinths.
There are over 200 species of geraniums to choose from. Their leaves can range from solid and heart-shaped to fragrant and fernlike. Geraniums bloom all summer long and well into fall, providing your pot with endless amounts of color and beauty. They like full sun but will wilt in very hot summer heat.