When people think of coleus, they may think of a drab little shade plant that their grandmother grew, says garden writer and coleus connoisseur Steve Silk. But coleus has surged in popularity, due in large part to new cultivars that grow — and thrive — in full sun.
"The best thing about putting them in the sun is that the colors are much more intense and vivid," he says. "If you leave them in the shade, they'll get dull."
From small leaves with ruffles to large leaves with bold margins, all in a variety of in-your-face colors, it's easy to see why this summer annual is coveted for its foliage. The flowers pale in comparison and are generally removed to promote plant growth elsewhere. You don't want these plants expending energy for flower production.
While new cultivars are able to handle the heat, they stall when temperatures drop below 50 to 55 degrees F. And even the slightest hint of frost causes damage to the plant.
Trimming coleus makes for bushier, sturdier plants. Sometimes a coleus gets a little too tall or grows unevenly, so cutting it back gives it a more uniform shape. Save the cuttings for making new coleus.
Coleus can be started from seed, cuttings, transplants or potted plants purchased from the nursery. Just give them the basics and watch them take root. "This is a plant that just wants to grow. Provide it with enough light, decent soil and enough water, and it's going to grow quickly," says Silk.
To grow your own from cuttings, first prepare the soil mixture. Silk likes to use one part perlite combined with one part potting soil. As he mixes, he adds enough water to make the soil as moist as a lightly squeezed sponge. "It often takes more water than you think because the perlite absorbs more moisture," he says.
Once the soil mix is ready, fill pots with the mix and make two-inch-deep holes for each cutting, using a pencil or your finger. Before planting, the cutting needs preparation. Remove any flowers by cutting back to a pair of leaves. This will force the plant's energy into making roots.
Silk recommends keeping three sets of leaves. After the fourth set, he cuts the stem and removes the bottom leaves. "Where I cut the branches off at the bottom is where the first new roots are going to form," he says. Then stick the wound of the cutting into the rooting hormone, a product that kickstarts root growth. Lightly tap off the excess hormone from the cutting and stick it into the hole, firming the soil around it.
Place the pots with cuttings on a tray and water the tray, instead of the plants, so you don't wash away the rooting hormone. Then place the tray in the shade, keep it watered and wait for roots to form. After a couple weeks or so, check the bottom of the pot. When roots start coming out of the bottom of the pot, the coleus is ready to plant in the garden.
The next step is start planting. "What I like to do is move slowly from one color to another and link them back and forth from plant to plant so it makes a smooth sort of seamless tapestry," he says. One coleus leads to another: 'Japanese Giant', the chartreuse green 'Amazon', the orange 'Smallwood's Driveway'.
A word of warning when planting coleus: even an extra hour or two of sunlight may affect the plant's coloring. Colors can change radically, which is something to keep in mind when picking them out at a garden center. Consider how much light they are growing in and how that will change once you plant it at home.
Container gardening with coleus
If you don't have a lot of room to grow coleus in your garden, use them in containers. Pair different selections together or with complementary plants. Silk recommends fertilizing with liquid 20-20-20 about once a week.
Overwintering indoors on a sunny windowsill is one solution, but does have drawbacks. "Coleus are fairly popular as houseplants, although I'm not quite sure why. They tend to be magnets for spider mites and white flies in particular," says Silk. When infestations occur on houseplants, he uses rubbing alcohol or horticultural soap to eliminate the problem.
If you bring coleus indoors for the winter, don't worry if it begins dropping leaves. That's the plant's way of adjusting to less light and cooler temperatures.