Research supported by the American Floral Endowment was initiated more than 15 years ago by Dr. Jeff Kuehny (LSU) and myself and his graduate students to develop species of Curcuma and Globba gingers for cut flower and potted plant uses. At the time, flowering was considered mainly for summertime as this is their normal season for flowering. Reports of this research can be found at http://endowment.org/afe-floriculture-and-horticulture-research-reports/. These tropical gingers with their white and soft pink to lavender colors would have much appeal for spring holidays if they could be forced for this season.

About 65 species of Curcuma are found in southeast Asia, with a number of these produced for export of rhizomes and cut flowers. With their charming flowers reminiscent of tulips, C. alismatifolia has been exported from Thailand since the early 1990s, first for cut flowers, and later, as breeding and selection progressed, short-stemmed pot varieties were developed.

The genus Globba is composed of 40 to 100 species distributed throughout the Malaysia-Southeast Asia region into India and southern China. Plants are usually less than three feet tall with small rhizomes and fleshy storage roots. While they mostly grow in shady areas, species can also be found in moist to dry grasslands. The spectacular purple to white and green pendent flowers are produced during the long days of summer at the tips of upright leafy shoots.

As long-day plants, Globba species go into dormancy in the fall months; thus, daylength extension is required to maintain flowering as with Curcuma alismatifolia.

Both genera respond to short days by going dormant, and rhizomes are harvested in late fall-winter, air dried, and exported in late winter to markets in temperate areas where they are forced. Research by Maria Pilar Paz, a graduate student with Dr. Kuehny, found that rhizomes could be stored for up to 4 months and still could be forced into good flowering. The problem with obtaining a longer season of flowering has been the availability of rhizomes earlier or later in the season.

In Hawaii, after the AFE research was completed, I held onto some rhizomes and increased numbers for several years. By using artificial short days, I could induce the rhizomes to go dormant. When dormant, they could be stored and brought out after a period of time for forcing. For winter flowering, this also meant that long days had to be provided, which was done with a 4-hour night break interruption.

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The Curcuma studies were carried out over several years using Chiang Mai Pink (CMP), Supreme, and Climax C. alismatifolia rhizomes produced in Hawaii so that dormancy and storage times could be controlled. Rhizomes were initially produced in field conditions (Supreme, Climax) in Hawaii and dug in February while still dormant, but later, they were grown indoors in controlled short-day (8-10 hours) conditions so out-of-season dormant rhizomes could be obtained.

Rhizomes were cleaned of substrate and air-dried for 4-6 weeks, then held in a dry peat medium in plastic bags at 60F until planting. Rhizomes stored at 54F had lesser survival and did not survive when stored at 48F. Curcuma rhizomes were started and grown out, brought into dormancy, stored, and forced over three different years to create a monthly serial planting schedule. Greenhouse air temperatures ranged from 77 to 102F, depending upon season (Hey, this is Hawaii!).

Potted plants of G. sherwoodiana ‘White Dragon’ were allowed to go dormant under natural short-day conditions in Hawaii. The rhizomes were extracted from the potting medium and air-dried for 3 weeks in shaded conditions in a greenhouse (mean temperature of 75F). Large rhizome masses were cut into units with one or two growing points, and dry rhizomes were packed into plastic bags of dry vermiculite and placed in storage at 60F. We started storage in April and removed batches of rhizomes monthly, beginning in July, for forcing over the next 12 months. Fewer rhizomes survived long-term storage as evidenced by lower numbers that sprouted in the following May and June plantings.

Both Curcuma and Globba were grown in 6-inch standard pots. For both gingers a peat-perlite medium amended with a controlled release fertilizer (Osmocote 18N-2.6P-9.9K), treble superphosphate, dolomite, and Micromax™ elements (Scotts Products) at the rates of 17.6, 10.6, 2.1, and 3.5 oz. per 3.5 ft3, respectively were used. Irrigation was as needed until sprouting; thereafter, 1.2 fl. oz/pot/day. During the forcing and flowering period, light levels ranged from a mean summer high of 13 mol·m-2·d-1 to a winter low of 6 mol·m-2·d-1, including the 4-hour night break from 400 W HPS lamps. For both gingers, the temperatures in the glasshouse ranged from a high of 102°F to a low of 73°F in summer and from 90°F to 68 °F during winter.

The data recorded for both gingers were time from plant to sprout, defined as the day the first shoot appeared above the substrate, and from sprout to flower for each pot with flowering recorded for the first true flower to open on an inflorescence. These data enabled calculation of mean times to sprout (appearance of the first leaves above the soil), sprout to flower, and total production times from planting. While the data reported were for the first open flower on the first inflorescence, additional inflorescences were produced for both species during the following weeks.

Vase life was determined only for G. sherwoodiana. The true flowers last only one day, but vase life studies showed that the colorful Globba bracts could last up to 30 days! A related hybrid, ‘Blue Hawaii’ had similar keeping quality.

In three Curcuma forcing trials, plant-to-sprout times mostly ranged from 4 to 5 weeks. Forcing, as defined by plant-to-sprout times, can be delayed by cool substrate temperatures, or enhanced by a period of warm substrate temperatures. It is important to maintain a warm substrate temperature during winter forcing to keep plants growing and maintain crop schedules as rhizomes planted in December and January took longer to sprout than those planted in spring or summer. Sprout-to-flower times ranged from 65 to 99 days in the 2009-2010 summer trial, averaging 78 days with a plant-to-first- harvest time of 13 to 18 weeks, while the winter trial of 2010-2011 had a sprout-to- harvest range of 75 to 94 days, averaging 88 days, and a plant-to-first-harvest time of 14 to 20 weeks. A daily light integral (DLI) of at least 10 mol·m-2·d-1 is sufficient for floral stem development, but artificial daylength extension or night interruption is necessary during the short days of fall and winter to prevent the plants from slipping into dormancy. Figure 1 summarizes responses to planting times for the several forcing series.

Stored Globba rhizomes were quick to sprout once planted and placed in the greenhouse, averaging 12.2 ± 5.4 days. However, the rhizomes planted nine months after placement in storage required an extra week to sprout than the first several plantings, and were less vigorous. Sprout-to-first-flower durations increased from about 40 days to more than 60 days as time spent in storage increased. Production time over the 12-month period from plant to first flower averaged 61.8 ±16 days, with longer production times in the last plantings despite higher summer light levels (Figure 2). The delay is likely due to the rhizomes having lower carbohydrate reserves after the longer storage duration. Over the twelve months of series plantings, pots averaged an additional 4 flower stems in the 60 days after the first one was recorded. Length of the first stalk to flower averaged 19 + 1.7 inches across all seasons, but we got the longest stems during the high light periods.

Figure 1. Mean durations for plant sprout, sprout to first flower, and days from planting to first flower for Curcuma alismatifolia planted at diffrent seasons over a three year period. N = 10.

Figure 2. Mean duration for plant to sprout, sprout to first flower, and days from planting to first flower for Globba sherwoodiana planted monthly after a period of 15°C storage. N = 12.

Take-home message

To hit prime spring markets, rhizomes need to be planted in late fall and early winter, meaning that rhizomes either have to be stored for many months after receipt from Thailand in late winter, or programmed by short days during summer to go dormant by late summer. Storage at 60F for about 6 weeks seems to be optimum, although shorter durations can be used in conjunction with a post-storage treatment of two weeks at 77 to 86F, which shortens forcing time. Since forcing and development take a little longer in winter, planting intervals closer together than the one month we provided would enable more consistent flower production. Long-day lighting will be required during fall-winter to prevent dormancy.

Selected literature citations

Criley, R. A. 2013. Blueprint programming for year-around forcing of Curcuma alismatifolia. Acta Hort. 1000:209-216.

Criley, R.A. and H.-J. Kim. 2015. Year around production of Globba sherwoodiana ‘White Dragon’ cut flowers. Acta Hort. 1097:251-255.

Paz, M.P.,2003. Rhizome Manipulation Affects Growth and Development of Ornamental Gingers Master of Science Thesis, Louisiana State university, Baton Rouge, LA. http://etd.lsu/docs/available/etd-1110103/unrestricted/Paz_thesis.pdf

Paz, M.P., Kuehny, J.S., McClure, G. and Criley, R. 2003. Effects of rhizome storage time and temperature on growth and carbohydrate content of ornamental ginger. Acta Hort. 624:103-109.

Photo 1 – C. alismatifolia pink
Photo 2 and 3 – C. alismatifolia white and pink
Photo 4 – G. sherwoodiana ‘White Dragon’

Richard Criley

Emeritus Professor

Richard Criley is Emeritus Professor of Horticulture, University of Hawaii. Contact him at [email protected]