By David Alosi, U. C. Master Gardener

Coleus

Ornamental gardening is as much about shapes, textures and juxtapositions as it is about colors. Besides flowers, an excellent source of color in the garden is the multitude of plants with variegated and colored foliage. I doubt that any single group of plants comes remotely close to the rainbow of colors available in the leaves of the coleus, a common tropical plant that has been in and out of favor with gardeners since the 1800s.

Coleus is native to Java and other areas of Southeast Asia. It was introduced to Europe by Karl Ludwig Blume during his travels in the early 19th century. The plant was originally named Coleus blumei in honor of Blume, and it became extremely popular in Europe. Victorian "carpet bedding," a technique of making patterned flower beds using colored flowers and foliage, relied heavily on coleus to create bright and intricate patterns in the garden.

Coleus is a member of the mint family, Lamiaceae, which includes mint, basil, salvia and rosemary. One of the easily identifiable family characteristics is having square stems. Coleus has recently been reclassified botanically, and its new scientific name is Solenostemon scutellarioides. I find "coleus" a lot easier to pronounce.

Coleus plants are tender and won't live through Napa Valley winters unless brought indoors. Used as annuals, they add color to the garden from April to November. Coleus is currently enjoying a comeback, with several hybridizers working to create new and exciting cultivars that are now appearing in nurseries.

Coleus

Most coleus plants will tolerate full sun exposure but the colors of some can become dull and bleached out. They are happier in locations receiving morning sun, bright indirect light or partial shade.

Coleus plants are easy to grow. Plant masses of them together for bright color in a shady area. Combine them with other foliage plants or with flowering annuals for spectacular container plantings. The lower-growing varieties (6 to 12 inches) will create a colorful border, or you can use the taller types (up to three feet) as background plants. You can use branches of these larger varieties in long-lasting bouquets. They will add a lot of color and may grow roots in the vase before they are thrown out with the faded blooms.

Coleus has average water needs but should not be over watered. It performs best in evenly moist, fertile soil, although once established, it can tolerate some drought, making it a great choice for containers. The plants need excellent drainage and regular applications of nitrogen-rich fertilizer. Mulching with compost or wood chips is a good way to reduce their water needs.

Coleus is resistant to serious disease or insect problems when grown outdoors under good light and soil conditions. Pests to watch for include mealy bug, aphids and white flies. Potential diseases include stem rot and root rot, usually the result of poor drainage or over watering.

Coleus also makes a good houseplant in bright light. Some trailing varieties will perform well in hanging baskets. Propagation is easy. Start new plants by placing tip cuttings in water, which is also a good way to preserve plants over the winter, to be planted out after the last spring frost.

Plants benefit from frequent pinching to make them bushy and to prevent flowering. The flowers are generally blue to blue-violet and are small and inconspicuous. Coleus is also very easy to grow from seed planted in a warm location indoors in the spring or outdoors after the weather has warmed.

I really like the bright lime-green variety called 'Limelight' and the nearly black varieties, such as 'Black Knight' or 'Palisandra.' These tall varieties look great together in a large container. There are also some beautiful copper-colored varieties.