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AUTHOR

David Trinklein
University of Missouri
Division of Plant Sciences
(573) 882-9631
trinkleind@missouri.edu

2015: Year of the Coleus

David Trinklein
University of Missouri
(573) 882-9631
trinkleind@missouri.edu

Published: January 5, 2015

The National Garden Bureau has chosen coleus as its ornamental annual to promote in 2015. Thus, we now are in the “year of the coleus”. This colorful yet durable plant adapts well to a wide range of exposures and garden situations. Recent improvements made by plant breeders have brought about resurgence in popularity to this long-time favorite.

Mention coleus (the word is both singular and plural) to most gardeners and mental images of shade-loving plants with colorful leaves come to mind. Moreover, most gardeners today associate the name with one of several seed-propagated series of coleus grown for bedding plant pack sales in the spring. Coleus have long been prized for their colorful foliage which may combine shades of green, yellow, pink, red and maroon. New introductions of this popular annual have been selected for increased sun and heat tolerance, turning coleus into a “plant for all locations” in the annual garden.

The use of coleus as an ornamental plant dates back to well before the Victorian Era. Species of coleus are thought to be native to Indonesia and parts of Africa. Because coleus has been cultivated as an ornamental for so many centuries, its exact botanical origin is unknown, although Coleus blumei is most likely involved in its parentage. For that reason, for decades the scientific name of this member of the Lamiaceae (mint)family was Coleus x hybridus. Plant taxonomists recently reclassified coleus into the genus Solenostemon. Therefore, the correct scientific name for the plant today is Solenostemon x hybridus.

Dutch traders are credited with carrying several coleus species to Europe in the mid-19th century, where plants breeders in various parts of the continent began to hybridize it. Each tried to create new and more wildly variegated hybrids than their competitor. As a result, new cultivars often commanded outrageously high prices in the market. In the 1890's, both English and American gardeners adopted coleus with enthusiasm, both as a garden plant during the summer and a houseplant during the winter. Interest in this plant was so strong that the term “coleus craze” was used to describe the public’s enthusiasm for it during the Victorian Era.

Coleus is like a “comfort food” from childhood for most gardeners. It often was one of the first plants they grew because of its carefree nature. Later, many gardeners forsook coleus in favor of more ornate, “glamorous” species. Gardeners who have not tried coleus lately are in for a pleasant surprise, for great improvements have been made. The primary fault of coleus from yesteryear was their inability to thrive and remain attractive in full-sun settings. This was especially true for coleus propagated from seed.

Today’s coleus cultivars carry amazing sun and heat tolerance and are available in a broad range of leaf colors, sizes, shapes and textures. The variability in leaf color patterns is truly remarkable. Some cultivars exhibit solid leaf color, whereas others may feature splashes, blotches, streaks, flecks, margins and veins. Leaf color intensity may be affected by environmental conditions such as sunlight, heat and soil fertility. Bright sunlight tends to saturate colors and create a different appearance than that caused by part-sun/shade conditions. For this reason, the latter is the preferred exposure for most modern cultivars.

Of the several hundred cultivars of coleus on the market, about forty are considered to be sun-tolerant. The term “sun coleus” denotes cultivars that have been selected to tolerate more direct sunlight. Under these conditions, however, soil moisture considerations become even more important for good garden performance. As a rule, cultivars with darker colors tend to tolerate more sun than those with lighter colors. Morning sun and filtered afternoon shade has been shown to produce consistent foliage coloration, even for sun coleus.

Coleus should be planted outdoors after the danger of frost has past. They enjoy heat and dislike temperatures below 55 degrees F. Coleus tolerant of a wide range of soil conditions but good drainage is important. Poorly drained soil and/or excessive watering will result in stunted plants with dull colors and discolored leaf margins. Pinching growing terminals of young plants will encourage dense, compact growth. A mid-summer boost of liquid fertilizer at half-strength can be helpful in maintaining plant vigor.

When grown in properly prepared soil or in containers filled with a soilless medium, coleus is fairly resistant to serious disease or insect problems. An exception might be mealybug’s affinity for coleus as a food source. Occasional pests include slugs, snails, spider mites, whiteflies and aphids.

Coleus can be used in many different ways in the garden. Cultivars with solid leaf color can make a dramatic impact in the mixed border. Coleus make ideal companion plants for larger species and help to “fill in” vacant space under taller plants such as dahlia. In contrast, cultivars having leaves that vary in color may be used to echo the color of neighboring plants with similar (or contrasting) flower and/or foliage colors. Because of the multi-colored nature of their leaves, it is hard to find two coleus cultivars that do not go well together.

Additionally, coleus make excellent container plants. They often are used as the fillers in the requisite thriller, fillers and spillers that every well-designed container should have. More robust-growing cultivars should be pinched regularly to keep them properly proportioned to their container neighbors.

There are many, many cultivars of coleus from which to choose. Available in nearly every color combination imaginable, they range in size from dwarf cultivars such as the Wizard™ series to giants such as the Kong™ series. Personal favorites of the author include ‘Alabama Sunset’, Colorblaze® ‘Dipt in Wine’, ‘Lime Time™’ and ‘Sedona’, ‘Electric Lime’, ‘Henna’, ‘Honey Crisp’, ‘Indian Summer’, ‘Redhead’ and Stained Glassworks™ ‘Big Blonde’ and ‘Luminesce’.

In conclusion, consider coleus as you begin to make your garden plans for 2015. New, colorful cultivars of this low-maintenance annual can be found that fit nearly any garden or container setting. If you have not grown coleus for some time you are in for a pleasant surprise.

Credit: Excerpts of this article were used with the permission of the National Garden Bureau.

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REVISED: September 29, 2015