Flowering cabbage and kale should be started in mid summer for fall sales. The following is more information on growing flowering kale from the University of Maryland.
Flowering Cabbage and Kale
The flowering kales were very poplar back in the 1990s but have somewhat died-down in popularity since then. Keep in mind this is an 11 week crop so for late fall don’t start your plants until mid- July. The color really comes on when it starts getting cold at night. The seed for most commercial cultivars was developed by Sakata Seed America or Takii America. The seed is available through many different wholesale seed companies.
The shape of the leaf determines whether it is called flowering cabbage and or flowering kale. Cultivars with smooth leaf margins constitute the flowering cabbage group while those with divided or "fringed" leaf margins are considered flowering kale. Within the kale group there are two types: the most common are the "fringed leaved cultivars" which have finely ruffled leaf margins and a smaller number which are called "feather leaved cultivars" have leaves that are finely serrated and deeply notched. A grower should select depending on growth habit and coloration that your customers want.
In each series there is normally a white, pink, and red cultivar.
Flowering cabbage cultivars: Tokyo series, Osaka series, Pigeon (red, pink and white) and Color-up series
Fringe-leaved cultivars – Sparrow series, Chidori series and Kamone series (reds and whites), and Naygoya series
Feather-leaved cultivars – ‘Coral Queen’, ‘Coral Prince’, ‘Red Peacock’, and ‘White Peacock’
Culture: The tough part is that growing ornamental cabbage and kale in summer in Maryland can be challenging if the temperatures are high. Cabbage and kale grow best in cool weather (55º to 60º F) nights. Since outdoor temperatures frequently exceed this range during the summer, select a site which has good air circulation and is "relatively" cool.
With high temperatures in the summer there will be excessive stem elongation due to high temperatures. To prevent stem elongation make a 1500 to 3000 ppm B-Nine application when the plants have developed true leaves and before stem elongation occurs. Several applications (it might be as often as once a week) at the same rate may be made during July and August as needed. Do not apply B-Nine if the crop is going to be marketed as an edible crop. Plant
Nutrition: Maintain the substrate pH levels between 5.8 and 6.5. Many growers have used controlled release fertilizers with cabbage and kale with good success. Begin fertilizing at the rate of 50 to 100 pm N and K after seedlings emerge. Once transplanted, fertilize at the rate of 150 to 250 ppm N and K with periodic applications of a complete fertilizer such as 20-10-20. Make sure you keep the fertility and mist levels correct or the plants suffer. Lack of nitrogen will result in the plants turning yellow and losing lower leaves. Maintain fertilization until night temperatures drop and coloration begins which is October in Maryland. In October reduce fertilization to 50 ppm N and K. Excess nitrogent during this period will prevent good coloration.
Reprinted from the June 26, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center.