By Abigayle Ward, UConn Dept. of Plant Science & LA Graduate Student
Seen anywhere from great-grandma’s ornamental garden to your neighbor’s hanging basket, coleus are the colorful, velvet-textured leafy cousins of oregano and deadnettle. Native to tropical regions of Africa, Asia, and Oceania, it is thought that Dutch botanists introduced the fascinating foliage to Victorian England in the mid 1800s. Coleus were readily welcomed into homes as parlor plants and into ornamental gardens. They were especially coveted in so-called “carpet bedding” gardens, where bedding plants of equal height are used to create colorful designs such that they appear like “carpets” when viewed from above. Other than coleus, the Victorians enjoyed using colorful flowers such as petunias, asters, and zinnias as carpet bedding. Carpet bedding is still popular today; we have at least one such garden featuring coleus and petunias on display at the University of Connecticut Storrs campus. To design a carpet bedding garden, try combining simple shapes and lines to make symmetric, harmonious patterns. Use green vegetation, such as sedums, or even a green cultivar of coleus, to contrast with the bright colors of flowers and the mulch or soil below.
For those of us lacking yard space comparable to an English country house, a large carpet bed garden might be impractical. Instead, coleus can be planted alongside other flowers for a splash of color in a flower bed against a house or fence. Coleus are the perfect complement to the colorful clapboard siding characteristic of houses in New England – draw attention to the colors of both by putting reds with greens and yellows with purples. If coleus are planted directly into the ground, slugs are one major pest to look out for. In particularly wet summers, such as those in recent years, slug populations can devour entire coleus plants.
To avoid slugs, container gardens may be a wise option. Sitting above the ground and out of field soil, slugs will have more difficulty reaching the tasty, tender leaves. For those with outdoor space around their apartments, container gardens are also generally a renter-friendly option. Coleus grow well in window boxes and other small containers, and they can help add a warm, friendly atmosphere to the entrance of any home. Most cultivars of coleus available on the market today are tolerant of both shaded and sunny conditions, and thus are well-suited to either covered or open porches. In containers, the main pests to look for are thrips, mealybugs, and aphids. These three pests can cause discoloration in leaves, such as silvery/gold, yellow, or black spots. Outside where predators of these pests thrive, infestations should not progress to the point of killing entire plants, but affected foliage may be unsightly. While systemic insecticides may help keep these types of pests off coleus, they also can kill bees. Avoid applying systemic insecticides to coleus outdoors whenever possible. Try moderately forceful sprays with water instead, insecticidal soap or other least toxic controls.
The Victorians also kept coleus as houseplants, and so can you. In plant hardiness zones 6a-7b in Connecticut, coleus are very tender annuals. They will grow prolifically when temperatures are above 60°F, and will experience cold injury if temperatures fall below 50°F. When temperatures plunge below 40-50°F and overnight frost becomes a possibility, leaves will start to blacken and die. At the end of the growing season before the first frost, consider planting stem cuttings in pots and bringing them indoors for colorful, year-round foliage. Coleus as houseplants will do best in north-facing or east-facing windows. Avoid placing them in windows where they experience too much direct sunlight for too long during the day. If windows are unavailable, coleus also grow decently under grow lights.
No matter where they are grown, the main attraction of coleus is its brilliant foliage. Plants grown in containers may benefit from occasional nitrogen additions to keep them growing all season long. Like others in the mint family, coleus grow flower spikes when stressed or when the plant is near the end of its life cycle. While the flowers on the spikes are not very attractive from an aesthetic standpoint, bees, hummingbirds, and other pollinators flock to them. While the spikes can be pruned off if they appear too early in the growing season to encourage further vegetative growth, consider leaving the late-season spikes on, so that bees can collect nectar to sustain their hives over the winter.
While the selection of coleus cultivars were limited in Victorian England, decades of horticultural breeding efforts have given us access to over 1,000 varieties today, including sun-tolerant cultivars, with endless colors, leaf shapes, sizes, and growth habits. Consider adding this versatile Victorian dream to your home garden for splashes of colorful summer foliage.
If you have questions on coleus or on other gardening topics, feel free to contact us, toll-free, at the UConn Home & Garden Education Center at (877) 486-6271, visit our website at www.homegarden.cahnr.uconn.edu or contact your local Cooperative Extension center.