As other presentations in this colloquium have shown, the definition of high tunnels is rather broad, but emphasizes in-ground production of crops in simple frame structures usually covered by a single layer of clear polyethylene. Thus, when considering production of floral crops in high tunnels, the emphasis is on flowering plants grown for cut flowers, rather than other categories of floriculture products such as bedding plants, potted flowering plants, and foliage plants that are normally grown in containers (Table 1). It may be helpful to briefly summarize the worldwide and North American production of cut flowers, for which the use of high tunnels has become important.
Production of floriculture crops in the United States in 2005 (Jerardo, 2006).
The production of cut flower crops worldwide has undergone profound changes in the last 40 years. Whereas the major cut flower crops [rose (Rosa spp.), carnation (Dianthus caryophyllus), chrysanthemum (Dendranthema ×grandiflorum), and alstroemeria (Alstroemeria spp.)] were grown within North America largely for local consumption, they are now almost exclusively imported from South America (Tables 2 and 3) into the United States (Stewart, 2007). Domestic production used to be concentrated in greenhouses, but energy and labor costs became prohibitive, and the more ideal year-around production environment and low cost of labor in the countries near the equator made that shift inevitable (Pertwee, 2003).
Cut flower sales in the United States, and the proportion produced in the country (Stewart, 2007).
United States cut flower imports by country of origin (Stewart, 2007).
High tunnels are widely used in these countries to protect the flowers from rain and wind (Stewart, 2007) (Fig. 1). While production statistics are not separately gathered for flowers grown in glass-covered greenhouses or plastic-covered high tunnels, it is estimated that the majority of the 15,000 ha of flowers grown under protected cultivation in China are grown in the ground in high tunnels (Jiang et al., 2004). The cultivation conditions for roses grown as cut flowers worldwide have been most fully described (Pertwee, 2003), and show that protected cultivation is the norm for countries near the equator, where currently the majority of cut-flower roses are grown (Table 4).
Worldwide rose production areas (Pertwee, 2003).
Albright, L.D., Seginer, I., Marsh, L.S. & Oko, A. 1985 In-situ thermal calibration of unventilated greenhouses J. Agr. Eng. Res. 31 265 281
Blacquiere, T., Straver, N. & van den Berg, D. 2002 Possibilities for using photoperiodism to program flowering of sunflowers (Helianthus annuus) in the greenhouse and in the open Acta Hort. 580 101 109
Jerardo, A. 2006 Floriculture and nursery crops yearbook 5 Mar. 2008 <http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1448>.
Jiang, W., Qu, D., Mu, D. & Wang, L. 2004 Protected cultivation of horticultural crops in China Hort. Rev. (Amer. Soc. Hort. Sci.) 30 115 162