Coleus care: bright color indoors and through winter

Light

Indoors, light is the limiting factor. NC State states that coleus grown as a houseplant requires bright light, and Missouri Botanical Garden explains the two failure modes: too much shade makes plants leggy, and too much sun can make them wilt. A south or west window with a sheer curtain, or an unobstructed east window, reaches the high-light range of about 300 foot-candles on the University of Illinois Extension scale, and sun-tolerant cultivars can take direct light on top of that.

Cultivar matters more than with most houseplants. Traditionally, coleus grew best in part shade, but UF/IFAS has bred many varieties that thrive in full, hot sun, and Clemson notes that types that are not sun-tolerant bleach and discolor in full sun. Check the label. A shade type on a hot south sill fades and droops by afternoon, while a sun type in a dim corner stretches and loses its color.

Water

Coleus likes steady moisture with good drainage. Missouri Botanical Garden says the soil must not be allowed to dry out, and UF/IFAS asks for soil kept lightly moist at all times. Clemson's practical test, written for planted coleus, works indoors too: water when the entire top inch of soil is dry. Pots dry faster than beds, and Clemson notes that container coleus need frequent watering. Water thoroughly until it drains, then empty the saucer.

Too much water is just as damaging. Clemson describes plants with wet feet as stunted, with muddy brown leaves and scorched leaf margins, and lists root rot and stem rot among the fungal problems that excessive soil moisture brings on. Wetting the foliage encourages downy mildew, so pour at the base. Room-temperature water, as the University of Illinois Extension recommends, avoids chilling the roots.

An overwintering plant indoors grows far more slowly than a summer plant on the patio. Keep using the top-inch test in winter; the pot will simply need water less often, especially on a cool windowsill.

Soil and pH

Use a loose, very well-drained mix rich in organic matter. NC State and Missouri Botanical Garden both describe moist, rich, loose soil, UF/IFAS asks for well-drained soil amended with lots of organic matter, and Clemson stresses a very well-drained mix for containers. A peat-based potting mix with extra perlite does the job. Always use a pot with a drainage hole.

Humidity

None of the extension sources sets a humidity requirement for coleus, and it grows well in ordinary room air. The main indoor risk comes in winter, when the University of Illinois Extension says most homes fall below 30 percent humidity. Keeping the plant away from heating vents, grouping it with other plants, or setting it on a tray of wet pebbles with the pot above the water line is enough.

Temperature

Clemson describes coleus as a tender annual killed by the first frost, so bring pots indoors before fall nights turn cold. The extension sources give no indoor range for coleus itself; the University of Illinois Extension's general rule for foliage plants applies: 65 to 75°F (18 to 24°C) by day, 5 to 10 degrees cooler at night, and nothing below 50°F (10°C) for long. Clemson germinates seed at 70 to 75°F, a sign of how much this plant likes warmth.

Fertilizer

Feed for leaves, not flowers. Clemson recommends an all-purpose soluble fertilizer such as 24-8-16 or 17-4-17 for outdoor plants in June, July and August, and warns against fertilizers made for flowering, because the extra phosphorus makes coleus leggy and pushes it to bloom. Indoors, follow the University of Illinois Extension guideline of feeding no more than once every one to three months from spring through summer, and stop in winter when growth is slow.

Work out the dose for your watering can with the fertilizer dilution calculator →

Repotting

Pot up in spring or early summer when roots escape the drainage hole or the plant wilts between normal waterings, the signs the University of Illinois Extension gives. Many growers do not keep one coleus for years at all. An overwintered plant often turns woody and bare at the base by spring, and a few rooted cuttings in fresh mix make a better plant than repotting the old one.

• Roots grow out of the drainage hole
• The plant wilts between normal waterings
• The stems are woody and bare at the base

Propagation

Coleus is one of the easiest plants to root. NC State and Missouri Botanical Garden both say cuttings root easily in water or clean potting soil. UF/IFAS describes cutting a 2 to 6 inch piece of stem, trimming it half an inch below the lowest leaves, removing those leaves and setting it in moist potting soil or vermiculite in a shady spot for a couple of weeks until roots form. Clemson adds two cautions: patented cultivars, labeled PP or PPAF, should not be propagated by cuttings, and vegetative cultivars are sterile and cannot be grown from seed. Seed-grown types can be sown uncovered at 70 to 75°F and sprout in a week and a half to two weeks.

Methods: Stem cuttings in water or potting mix, Seed (seed-grown cultivars only) · Best season: any time of year; late summer to save plants before frost.

Common problems

Light and flowering cause most indoor complaints. Wilting in sun, bleached color and leggy stems all trace back to placement. Flower spikes appear in late summer, and Clemson notes that if they are allowed to go to seed the plant declines; shearing or pinching them extends its life. Aphids, whiteflies and spider mites are the pests NC State and Missouri Botanical Garden expect on indoor plants, and Clemson adds mealybugs. Clemson treats them with insecticidal soap.

Not sure which one it is? Try the plant problem diagnosis tool →

Is the coleus toxic to cats and dogs?

Treat coleus as toxic to pets, with one caveat. The ASPCA lists Coleus as toxic to dogs, cats and horses, with essential oils as the toxic principle and signs including vomiting, diarrhea, depression and loss of appetite, occasionally with blood. Its entry, however, is filed under Coleus amboinicus, the herb known as Indian borage, and the ASPCA has no separate entry for the ornamental Coleus scutellarioides. NC State rates the ornamental coleus as low severity for people, mainly minor skin irritation or an allergic rash after repeated handling. Keep it out of reach of pets that chew plants.

Check any other plant against the ASPCA lists →