Officially, ornamental cabbage and kale are cool-season biennials. This means they grow their vegetative leaves the first year and then send up flowers the second year, producing seeds before the plant dies. However, these fast-growing plants are usually grown as annuals for their showy foliage, planted from nursery starts in the fall or early spring, then removed from the garden after the seasonal display is concluded.
Light
These plants prefer to grow in full sun. However, when grown in warmer climates, partial afternoon shade is ideal.
Soil
An organically rich, loamy soil that drains well is ideal for these plants. Both cabbage and kale prefer a slightly acidic soil pH of about 5.5 to 6.5.
Water
Keep the plants well-watered; they like soil that’s consistently moist but not soggy. If the top inch of soil is dry, it’s time to water. If your climate provides regular rain, you probably won’t have to water at all. But be prepared to add supplemental water during a dry spell. Like many plants, about 1 inch of water (rainfall and/or irrigation) is perfect for these plants, but try to avoid overwatering.
Temperature and Humidity
Ornamental cabbage and kale don’t develop their full colors unless they get a good chill from a frost. They can last throughout the winter, but their appearance depends a lot on the weather. If it’s hot with long daylight exposure, they will bolt (send up a flower stalk and go to seed). And if it’s very wet with harsh storms, the plants will quickly become tattered. They can survive as long as temperatures remain above 5 degrees Fahrenheit. However, a sharp drop in temperature can damage or kill plants. Humidity typically isn’t an issue for these plants. But if the weather is damp and the plants don’t have good air circulation, they might develop fungal diseases, which usually appear as spots on the leaves.
Fertilizer
Fertilize ornamental cabbage and kale only at planting time using a balanced fertilizer. Don’t fertilize while they’re growing, or they can lose color and get leggy.
Types of Ornamental Cabbage and Kale
Unless you are growing commercially, there’s not much variety to choose from when it comes to ornamental cabbage and kale. Most seed packets are simply labeled “ornamental cabbage.” So it’s best to focus on a color combination that appeals to you. Flowering kales can be divided into “fringed-leaved cultivars” (those with ruffled leaves) and “feather-leaved cultivars” (those with finely serrated leaves). Some popular varieties include:
‘Chidori’ ornamental kale: This plant has very curly leaf edges with leaves that are purple, creamy white, or deep magenta.‘Color Up’ ornamental cabbage: This grows upright with green leaves and centers of white, pink, or fuchsia.‘Osaka’ ornamental cabbage: This ornamental cabbage has large, smooth leaves with center colors of pink, red, or white. The plant typically stays compact.‘Peacock’ ornamental kale: This plant looks more like its edible kale cousins, with loose growth and deeply serrated leaves in red, purple, or white.‘Pigeon’ series ornamental cabbage: This variety has a flattened shape with red or white centers.
Propagating Ornamental Cabbage and Kale
These biennial plants are generally discarded before the second season when they flower and set seeds. But if you do allow them to remain in the garden to produce seeds, the seeds can be collected from the faded flower heads and replanted at the appropriate planting time. You can store the seeds in the freezer to preserve them for later planting.
How to Grow Ornamental Cabbage and Kale From Seed
For spring plants, cabbage or kale seeds should be started indoors about eight weeks before the last expected frost date. For fall display, start the seeds about July 1, then plant the seedlings into the garden in mid-August. Start the seeds indoors in small pots filled with a seed-starter mix. Plant the seeds about 1/4 inch deep and keep the soil moist in a bright location at about 70 degrees Fahrenheit. The seedlings will emerge in 10 to 21 days, and the potted seedlings can be planted outdoors immediately after the last spring frost—or in mid to late August for fall/winter display.
Potting and Repotting Ornamental Cabbage and Kale
If you only want one or two plants, ornamental cabbages or kales often look more natural when grown in containers rather than scattered throughout a garden. They can make nice seasonal potted plants, much the way that potted pansies are used in the spring, and potted chrysanthemums in the fall. Choose a container with ample drainage holes, and use an all-purpose potting mix. Nursery plants likely won’t grow much larger than they are when you get them, so you typically won’t have to worry about repotting into a larger container.
Overwintering
Ornamental cabbages and kales are usually not allowed to overwinter, since the second year of these biennial plants leaves them rather unattractive as they send up flower stalks. But most gardeners will leave them in place well into the winter since the leave rosettes remain attractive until repeated hard frosts finally cause them to wilt.
Common Pests and Plant Diseases
Like many edible vegetables in the Brassica genus, ornamental cabbages and kales are quite susceptible to cabbage worms, cabbage loopers, flea beetles, caterpillars, thrips, slugs, and aphids. Hard water sprays can be used to dislodge many of these pests. A variety of pesticide dusts or horticultural oils designed for vegetables will also work on these pests. Cabbages and kales planted in pots may be less susceptible to pests and diseases than those planted in the garden. Common disease problems include leaf spots, blackleg, black rot, and yellows. These are most likely to occur when conditions are damp.
Common Problems With Ornamental Cabbage and Kale
Though used ornamentally, these plants are essentially vegetables and thus are susceptible to many of the common vegetable diseases and the pets that love to feed on edibles. Some notable problems you may notice include:
Holes in Leaves
This is almost certainly the result of one or more of the various feeding insects that love all members of the Brassicaceae family. Cabbage worms, a variety of other caterpillars, slugs, and aphids all view kales and cabbages as favored dining. A variety of insecticidal soaps or chemical sprays can be used to control these pests, and since these plants generally won’t be eaten, you can be more liberal in your use of chemicals.
Black or Yellow Spots on Leaves
Spots rather than holes in leaves usually indicate a fungal or bacterial infection. These are more likely to appear in damp weather conditions. Maintaining good air circulation can reduce the likelihood of these diseases. Fungicides may help treat fungal diseases if applied early enough.
Ugly Tall Stalks Appear
An otherwise attractive cabbage or kale that suddenly sends up a sparse and rather ugly stalk is in the process of bolting—going to flower. Its career as an ornamental plant is now over, though you can allow it to continue growing if you want to harvest the seeds for establishing new plants.
These are cool-season plants that are usually grown in the fall or early spring, discarded as the weather turns very cold or as the warm summer months arrive. They are left to grow right up into winter snowfall, where they can look magnificent with a cloaking of fresh snow.
