Fill a seeding tray with a lightweight, sterile potting mix suitable for starting seeds. Spread ornamental kale or cabbage seeds over the soil and moisten lightly with a spray bottle. Store the seeds in the refrigerator for one week. Ornamental kale and cabbage germinate best under cool conditions, such as those found in a refrigerator, but also need light. Don't cover them with soil. Start the seeds six to 10 weeks before the first expected frost. In northern climates, plant seeds in June. In the South, plant seeds mid-July. Once the seeds have germinated, move them to a cool, but light location in the house. Keep them moist and transplant them when they stand 4 inches high.
Buy transplants from a local nursery in early fall, if you prefer. Choose plants that are large in size because they won't grow much in your garden. These plants may cost more, but they'll fill up your garden and look better than smaller varieties.
Plant the seedlings in a flower bed or in a pot filled with a high-quality potting mix. Place the transplants so their bottom leaves touch the soil. Water the soil so it is evenly moist, but not soggy. Thereafter, water the plants to maintain even moisture.
Fertilize the plants every four weeks with a water-soluble fertilizer, according to package directions. Too much fertilizer may inhibit color development, so use the recommended amounts only.