The common coleus is a plant that comes in a wide range of colors and leaf forms. This plant, also known as Coleus scutellarioides, is native to Southeast Asia and is used as an herbal remedy in various cultures. Common coleus is a narcotic used by the Mazatec people of Mexico. In Cuba, this plant is considered invasive.
I. Appearance and CharacteristicsÂ
Coleus scutellarioides, commonly known as coleus, is a species of flowering plant in the family Lamiaceae (the mint or dead nettle family), native to southeast Asia through to Australia.
Another common name is painted nettle, reflecting its relationship to deadnettles (Lamium species), which are in the same family. (True nettles and their close kin are in the distant family Urticaceae.) The synonyms Coleus blumei, Plectranthus scutellarioides and Solenostemon scutellarioides are also widely used for this species.
Coleus scutellarioides is an upright annual or short-lived perennial plant. Although certain forms (such as the cultivar ‘Lime Time’) may grow as tall as 1 m (3 ft), with well-branched, (generally) four-angled stems, most Coleus stay less than 60 cm (2 ft). Shorter, more trailing forms have sometimes been described as separate species (under names such as Coleus pumilus or Solenostemon pumilus), but are all now considered part of the very variable C. scutellarioides. With modern cultivation and hybridisation, the species has become extremely variable with regards to its leaf colour, patterning and shape. They have somewhat fleshy, semi-succulent, but tender leaves, varying in size from 1.5–10 cm (0.6–3.9 in) long by 1–6 cm (0.4–2.4 in) wide; usually ovate in shape, the leaves are borne on petioles (stalks) from 0.5–5 cm (0.2–2.0 in) long. The leaf margin is divided to a variable degree. Hairs are present on both sides of the leaf.
The inflorescence is borne on the end of a stem and, like the leaves, is very variable in size; it may be up to 4 cm (1.6 in) long, with few or many flowers. The calyx is bell-shaped, initially only 1–2 mm (0.04–0.08 in) long, but lengthening to 5–7 mm (0.2–0.3 in) when in fruit. The bluish-purple petals are joined to form a typical two-lipped labiate flower, 8–10 mm (0.3–0.4 in) long. The stamens are joined for about half their length and are covered by the upper lip of the flower. The fruit is described as a “nutlet”, and is black, about 1 mm (0.04 in) long.
Pigmentation
The leaves of the wild species may be somewhat variegated, but this has been developed to an extreme degree in cultivated varieties, whose leaves may include one or more shades of green, white, cream, yellow, pink, red, maroon and dark purple. Green coloration is due to the amount of chlorophyll present in the chloroplasts in the leaves. Red, purple, pink, and orange colors are due to anthocyanins – water-soluble, flavonoid biosynthetic pigments, found in the foliage in addition to chlorophyll. The increase in anthocyanin production is accompanied by a decrease in chlorophyll production. The production of anthocyanins and chlorophyll is affected by light levels; the more light is present, the more anthocyanins are produced, with an inverse relationship to the production of chlorophyll. Anthocyanins are created inside the cell and facilitate photosynthesis in leaves that are exposed to very intense or prolonged sunlight by providing protection from damage caused by ultraviolet light. Some coleus cultivars over-produce anthocyanins and under-produce chlorophyll to the extent that optimal growth is prevented.
II. How to Grow and Care
Sunlight
How much sun to give your coleus depends on the variety you choose. Newer cultivars, like the Wizard series, are more tolerant of light than older types. Most varieties are suited to shady spots and do well with morning sun and afternoon shade.
Plants grown indoors usually get sufficient light during the growing season but may need to be supplemented with a grow light in winter.
Temperature and Humidity
Coleus thrives in hot, humid conditions. In temperate climates, light frost can kill large-leaved types. Move potted plants indoors or use an insulating cover when temperatures dip into the 50s.
Keep indoor plants away from air conditioner vents and drafts. In dry climates, the plants benefit from extra humidity. Wait until the temperature reaches 70°F before moving potted plants outdoors in spring.
Watering
Coleus plants grow best in soil that is consistently moist but not soggy. Long dry spells slow the plants’ growth, and leaves start to brown around the edges. Let the soil dry out between watering and water when the top inch of the soil feels dry to the touch.
Mulch helps retain moisture, but don’t use cedar mulch, which is toxic to coleus. Containers need water more often, up to twice a day during hot weather.
Soil
Coleus prefers consistently moist, rich, well-draining soil. Before planting, amend the soil with compost or another organic material. For potted plants, use a good-quality potting mix. Choose a container with drainage holes.
Fertilizing
Coleus is sensitive to fertilizer which can leech color from the leaves if overused. When grown in rich soil, feeding isn’t necessary. Amend the bed beforehand or add a balanced slow-release fertilizer at planting time. Feed container-grown plants once a month with a water-soluble fertilizer.
Want more gardening tips? Sign up for our free gardening newsletter for our best-growing tips, troubleshooting hacks, and more!
Pruning
For full, bushy plants, pinch out growing tips when plants are about 6 inches tall. Pinch just under the flower buds to promote leafy growth instead of flowers and seeds.
Plants not pruned tend to get leggy and lose their shape. This can happen with indoor plants during winter so give them more sun or supplement with artificial light.
Propagation
Coleus plants can be propagated by taking stem cuttings. Gather a sharp scissor, potting mix, small pots with plastic covering, and rooting hormone, and follow these steps:
- Use a sharp, sterile scissor to cut a 4- to 6-inch long stem making the cut beneath a leaf node.
- Remove leaves from the lower half of the cutting leaving one or two at the top. Large leaves can be cut in half to facilitate rooting.
- Dip the end of the stem in a rooting hormone compound to cover the bottom leaf nodes. Plant in moistened potting mix.
- Cover the container with plastic, making sure the plastic doesn’t touch the cutting.
- Place the covered cutting in a bright, warm location with a temperature at 70°F.
- Keep soil consistently moist. Roots develop in two to three weeks.
- Remove the plastic and continue growing the new plant in a bright, warm location.
How to Grow Coleus From Seed
It’s easy to grow coleus from seed. It takes about 21 days for germination and then three or four weeks of warm weather for fully grown plants. Modern coleus varieties sold in stores are hybrids grown from cuttings potted up for nursery sale, but you can still find seeds of many varieties. For planting outdoors, start seeds indoors about eight to 10 weeks before your last frost date. Here’s how to grow your own plants from seed.
- Sprinkle tiny seeds over a tray filled with potting mix and press them lightly into the soil. Do not cover.
- Add a plastic dome or cover and set the tray in a bright, warm spot with temperatures between 70 and 75 degrees F. Germination occurs in three weeks.
- Remove plastic and continue to grow the seedlings keeping soil consistently moist.
- When two sets of true leaves appear and seedlings are sturdy enough to handle, transplant them into their own pots until outdoor planting time. Make sure to harden off before planting in the garden.
Potting and RepottingÂ
Coleus grow rapidly so start with a pot large enough to accommodate the mature plant. For tall, upright varieties choose a heavy 12-inch pot like terra cotta to help anchor heavy top growth. Choose containers with plenty of drainage holes.
Pests and Diseases
Common Pests & Plant Diseases
Groundhogs and young rabbits will nibble your coleus leaving them with an unsightly ragged appearance. Protect plants early in the season to deter pests. Watch for mealybugs, aphids, spider mites, whiteflies, and slugs. Insects can sometimes be controlled with a strong spray from a garden hose. Mulch discourages slugs.
Coleus is not usually bothered by disease. Cool, damp weather can lead to fungal disease like powdery mildew. Good drainage discourages root and stem rots.
Common ProblemsÂ
Coleus is a reliable, showy foliage plant with few problems. Fungal infections can set in during periods of cool, humid weather. Here are a few issues that may crop up.
Yellow Leaves
Chlorosis causes leaves to turn yellow, tracing back to a number of problems usually due to errors in care. Overwatered plants develop yellow, mushy leaves. Underwatering causes foliage to fade, yellow, and turn brown and crispy.
Too much fertilizer interferes with chlorophyll production. Use a balanced formula in the garden only in cases of poor soil and a water-soluble product for container plants. Choose the correct pot size starting out. Rootbound coleus also develops yellow leaves.
Leaf Spores
Downy mildew is a fungal infection that flourishes in cool, humid conditions causing stunted growth and loss of foliage. Fuzzy gray and purple spores appear on the undersides of leaves affecting lower leaves first. Avoid overcrowding plants for better air circulation and water in the morning. Remove infected leaves.
Wilting
Big leaf cultivars may wilt following transplant into the garden or if they receive too much direct sun. Make sure the variety you choose is suited to sun exposure for the intended garden spot. Water new transplants in well and keep soil moist but avoid overwatering.
III. Uses and BenefitsÂ
- Ornamental uses
Common coleus is a herbaceous perennial commonly found in tropical gardens. It is prized for its attractive bi-color leaves and year-round interest. Its bushy appearance makes it suitable for ornamental fencing. It is also appropriate for borders and beds. Common coleus is essential for tropical-themed gardens. Suggested companion plants include Black-Eyed Susan or Dahlia for color contrast.
- Other uses
Coleus scutellarioides, under the name Coleus blumei, has been reported to have very mild relaxing and/or hallucinogenic effects when consumed. The effects of the plant have not been scientifically explored in great detail, but the plant is known to have been used by the Mazatec people of southern Mexico for its mind-altering effects.
IV. Types of Coleus
There are hundreds of coleus plant varieties available in different colors, leaf textures, and patterns. New cultivars are developed each year, and garden centers tend to focus on a select popular few. Shop several different places to find more unique varieties. Some types to look for include:
Wizard series: Small 12- to 14-inch plants in standard color mixes easy to grow from seeds.
Kong series: These varieties feature 6-inch leaves on 2-foot tall plants sensitive to direct sunlight.
‘Black Dragon’: A unique variety with deep burgundy leaves and ruffled edges that grow to 18 inches tall.
Premium Sun series: Cultivars bred to tolerate full sun.
Fairway series: Dwarf cultivars growing 6 to 10 inches tall in a variety of leaf patterns and colors.
