Ornamental or flowering cabbage comes from the same family as edible cabbage, the Brasseca family. They are edible, but a better use is to ornament the landscape after frost has killed off most other plants. Ornamental cabbage is a biennial growing leafy the first year and producing unsightly reproductive growth the next. Because of this, it is usually grown as an annual. Timing of planting is important to get the rich reds, pinks and whites of the mature plant. Ornamental cabbage is a cool-weather plant and must be started late summer to early fall for best results.
Sew seeds six to eight weeks before the first expected frost, as they need cooler temperatures to germinate and to mature at the right time. Fill 6- to 8-inch pots or seed trays with commercial potting soil. Do not use soilless mix as it does not retain enough water for the seedlings. Space seeds about 5 inches apart and do not cover seeds as they need light to germinate. Germination will take place in about 10 days.
Transplant seedlings in seed trays to larger pots before the roots become pot-bound. The best time to transplant is when they have their first set of leaves.
Place plants outside, if grown indoors, once night temperatures reach 4.44 to 10 degrees C. Color will not appear until temperatures go below 60 degrees, and it takes about three weeks to fully change.
Purchase transplants from a nursery (if seeds were not started) in September when mums go on sale. Do not plant ornamental cabbage too early because the centres will grow leggy and not change colour. Plant transplants in 6-inch or larger containers or in the ground 12 to 18 inches apart. Plant in a sunny area with rich soil that is moist but well-drained. Plant so that the bottom leaves touch the surface of the soil.
Water plants well as all cabbage requires a good deal of moisture. Cover the soil with a layer of mulch to retain moisture.
Fertilise with water-soluble 20-10-20 fertiliser after cabbage is planted or pretreat area before planting with slow release 12-6-6 fertiliser at 0.907kg. per 100 square feet.
Use for fall landscaping in containers or right in the garden. Ornamental cabbage survives temperatures to 0-15 degrees C and lower.
Once roots are bound, the plant stops growing, so transplant into 6-inch or larger pots soon after they grow a few leaves. Fertilise plants before they reach full maturity as continuous fertilisation can affect the colour.