Choose a container with drainage holes. Consider the area you will place the container and pick the size accordingly. Cluster containers in odd numbers. In a full sun area with little shade, a terra-cotta pot is not a good choice, as this clay material will absorb heat and transfer it to the soil, making it difficult to keep plants adequately hydrated.
Pick plant varieties that will require the same level of sunlight. Shade-loving hellebores, for example, will not make good neighbors for the sun-worshipping Japanese anemone. Full-sun partners that will enjoy all day, direct light include royal purple angelonia, silvery blue salvia, candy-colored verbena and white trailing lobelia. Mix pairs of shade-loving, brightly variegated coleus with striped hostas or pink impatiens, crisp white alyssum and deep pink, pendulous fuchsias.
Choose plants with similar proportions that will fill out the container, varying in height for maximum interest and best use of horizontal and vertical space. For example, a small container with one large plant, such as an agave, might show off the dark foliage and interesting leaves as well as the beauty of the pot to the best advantage. A large container needs three to five different plants with varying leaf shape and heights, like tall snapdragons, lacy-leaved leopard's bane, a graceful miniature rose and trailing diascia.
Complementary colors, located across from one another on the artist's color wheel, will provide interest and contrast. Reds and greens, blues and yellows and purples and oranges are complementary shades. Analogous colors, which reside next to one another on the wheel, will provide a gentle variation of hue. Examples include yellow to orange tints, red to purple hues and blue to green shades.
Consider the shape of plant foliage, petal forms, and texture of leafy plant parts to provide interest and detail in your containers. Feathery fountain grass, soft furry lamb's ear, and chubby succulent sedum all bring the eye and the hand in for a closer inspection. Dusty miller plants have silvery, velvet fuzz on softly rounded leaves and the coleus and hosta offer rippled, thick, leathery surfaces to delight the senses.