W. Garrett Owen, PhD Student and Floriculture Technician, Purdue University; Roberto G. Lopez, Ph.D., Associate Professor & Floriculture Extension Specialist, Purdue University
Ornamental cabbage and kale (Brassica oleracea var. acephala L.) are important fall crops among asters, chrysanthemums, pansies, and other cold-tolerant bedding plants. Like many bedding plant crops, greenhouse growers encounter production challenges with ornamental cabbage and kale.
Lower leaf yellowing (chlorosis) and leaf loss may be attributed to two cultural conditions: 1) water stress and 2) excessive or deficient fertility.
Ornamental cabbage and kale are often transplanted during summer months for fall sales. During these months they may experience water stress, thus resulting in lower leaf yellowing and loss. Additionally, high substrate electrical conductivity (EC) in addition to excessive drought stress can also cause lower leaf loss and root death. To prevent this from occurring, growers must provide plants with adequate moisture and maintain substrate EC. Appropriate container selection, substrates with increased water holding capacity, and automated irrigation systems are recommended.
Fertilizer recommendations vary for ornamental cabbage and kale production. Excessive fertilization >250 ppm nitrogen (N) will prevent intense coloration and can also cause marginal tip burn (Fig. 1).
However, discontinuing fertilization will not enhance center head and color development. It will result in chlorosis (Fig. 2), purpling (Fig. 3), or loss of lower leaves (Fig. 4). During periods of active growth, it is recommended to fertilize with a balanced fertilizer providing 150 to 250 ppm N, maintain a substrate pH between 5.5 and 6.2, and EC levels between 1.0 and 2.5 mS/cm.
Ornamental cabbage and kale are typically grown outdoors, but can be grown in greenhouses. High greenhouse temperatures during production can cause excessive stem elongation.
Plants exposed to night temperatures between 45 and 50 ºF for 2 to 3 weeks will develop full color without lower leaf chlorosis, purpling or leaf loss.
Ornamental cabbage and kale are prone to a number of insects and diseases. The most common include: aphids (Fig. 5), caterpillars, flea beetles (Fig. 6), and whiteflies. The most common diseases of ornamental cabbage and kale include: Alternaria leaf spot, Black rot, Club rot, Downy Mildew, Fusarium yellows, Rhizoctonia stem rot, and root rots caused by Pythium and Phytophthora.