Cool calceolaria

Why, in the heat of the summer, is it a great time to be thinking about winter production? First, it may feel good to think of those frosty January temperatures right now! But more importantly, now is the time to be planning your winter production — from scheduling space requirements to preparing for transplant production. Crops such as cyclamen, primula, and cineraria are staple cool-season crops. But what else can we grow to beat the winter blues? Calceolaria (Calceolaria × herbeohybrida), or pocketbook plant, is another crop that can be considered “cool,” not only for the air temperatures used in the greenhouse for growing them but for their unique flowers! This Production Pointers is going to focus on calceolaria, an underutilized flowering plant for winter and early spring production.

Calceolaria is a flowering potted plant with interesting pouch-shaped flowers (Fig. 1). While the flowers resemble the flowers of slipper orchids, calceolaria are in the same family as snapdragon and penstemon (Scorphulariaceae or figwort family). Flower colors are warm, ranging from red to orange to yellow (Fig. 1), with some bicolored cultivars (Fig. 2) available. Some solid-color cultivars also have spots.

Calceolaria are propagated by either stem tip cuttings or seed, depending on the series. Regardless of which type you are going to produce, it may be worthwhile to purchase seedling plugs or rooted liners for your production. Bringing in young plants may be easier than growing your own.

Plant young plants into containers filled with a standard peat-perlite substrate. Calceolaria does not have a specific pH requirement and is grown well in a general pH range of 5.8 to 6.2. Furthermore, calceolaria are low-feeding plants and EC should be maintained between 1.0 to 1.5 mS·cm-1 using 100 to 150 ppm N from a fertilizer with a high proportion of nitrate. If you are using cool temperatures for production, ammonium toxicity may occur due to a lack of nitrifying bacteria activity.

Calceolaria can be grown cooler than most flowering bedding and potted plants. Average daily temperatures of ~64°F (i.e. 68°F days and 60°F nights) should be maintained when plants are first transplanted and you are bulking up vegetative growth. After plants are established in containers and you have achieved sufficient vegetative growth or “bulking,” you have several options. To induce flowering with cool temperatures, the air temperature should be dropped to ~50 to 55°F. However, plants can also be induced to flower under moderate greenhouse temperatures with the use of long-day lighting such as day-extension or night interruption, since their requirement for long days can be modified with air temperature. Under moderate or warm temperatures, calceolaria are long-day plants, whereas plants are day-neutral under cool temperatures. Some of the new series and cultivars have a day-neutral flowering response at cool or warm temperatures and can be forced to flower with no day length manipulation. Be sure to learn what the requirements are for the series you are interested in producing.

Plant growth regulator requirements depend on genetics. Some for the newer cultivars that have been developed were bred for compactness and, as such, require little to no growth regulation to produce nice plants. However, if they are required, chlormequat chloride (400 ppm) is an effective active ingredient and, if applied when buds become visible, can control unwanted stretch.

One of the primary postharvest concerns with calceolaria is botrytis or gray mold on the flowers. The flowers are somewhat delicate and botrytis can easily damage them, resulting in unmarketable plants. If possible, use sub-irrigation for calceolaria, especially once the flowers are visible during development. If plants are irrigated overhead, be sure to provide plenty of time for flowers to dry off before packaging plants, as wet flowers can be infected during shipment when they are enclosed in boxes.

Christopher is an assistant professor of horticulture in the Department of Horticulture at Iowa State University. ccurrey@iastate.edu