Abstract
High tunnels are becoming an increasingly important production tool for vegetable, small fruit, and cut flower growers in many parts of the United States. They provide a protected environment relative to the open field, allowing for earlier or later production of many crops, and they typically improve yield and quality as well as disease and pest management. Producers, ranging from small-scale market gardens to larger scale farms, are using high tunnels of various forms to produce for early markets, schedule production through extended seasons, grow specialty crops that require some environmental modification, and capture premium prices. The rapid ongoing adoption of high tunnels has resulted in numerous grower innovations and increased university research and extension programming to serve grower needs. An informal survey of extension specialists was conducted in 2007 to estimate numbers (area) of high tunnels and crops being grown in them by state, and to identify current research and extension efforts. Results of this survey provide an indication of the increasing importance of these structures for horticultural crop production across the country.
Producers of horticultural crops in the United States, and the research and extension specialists who assist them, are increasingly recognizing high tunnels as valuable tools to assist with season extension and crop protection. High tunnels are also sometimes called hoop houses or unheated greenhouses and they include a range of designs from single-span to multi-span structures that are usually covered with a single layer of 6-mil polyethylene greenhouse film. High tunnels may be constructed to be semipermanent, movable, or temporary, although they are usually considered temporary structures for purposes of property assessment and taxation (Blomgren and Frisch, 2007). Typically, high tunnels are unheated and are passively ventilated, but they must have water for irrigation, and are used to produce a wide variety of crops directly in the soil, or less frequently, in artificial media (Lamont et al., 2003; Heidenreich et al., 2008). In regions with winter snow and ice, the polyethylene film is generally removed from multi-span high tunnels during the winter months, while it is usually left on single-span tunnels, which are often used for the production of winter crops (Blomgren and Frisch, 2007).
Despite having been invented in the United States (Emmert, 1955), high tunnels have not been adopted as quickly by fruit, vegetable, and flower growers here as in many other countries (Wittwer, 1993). While high tunnels or overwintering structures have been widely used in the nursery industry, it was not until the early 1990s that research and extension professionals in the Northeast began to report the high potential of these structures for vegetable production (Wells and Loy, 1993), initially reporting their great advantage for early production of warm season crops such as tomato (Solanum lycopersicum). Multiple efforts, many by innovative growers (Blomgren and Frisch, 2007; Byczynski, 2003; Coleman, 1998, 1999; Wiediger and Wiediger, 2003), have contributed to today's increasing awareness of the potential value of high tunnels for early or extended season production of fruit, vegetable, and flowers of outstanding quality. Because of their low construction and operating costs, it is common for producers to recover their investment within 1 or 2 years (Blomgren and Frisch, 2007).
Today, the use of high tunnels is increasing rapidly in many places in the United States. There are many examples of research and extension programming and education resources being developed around the United States. (Jett, 2004; Jimenez et al., 2005; Lamont et al., 2002, 2005; Nennich et al., 2004). Information on the Internet about high tunnels and their uses has burgeoned over the past decade. Several universities, agencies, and businesses have published digital information about high tunnel construction and use. One university-sponsored website (Kansas State University, 2003) contains original content geared for grower and educator audiences, as well as links to other websites of interest. This website also provides access to an e-mail listserv that is widely used by growers, allied industry, and academics to ask questions and exchange information related to high tunnel use (Kansas State University, 2004).
To attempt to capture a snapshot of current high tunnel use nationwide, we conducted an informal survey of state extension specialists at land grant universities. We present the results of the survey in this article to highlight the growing body of high tunnel research, extension education, and usage by growers in the United States.
Materials and methods
From a list of horticulture extension educators at land grant universities compiled by W.J. Lamont, Jr., when he served as ASHS Extension Division vice-president, we selected the names of vegetable or food crops specialists to be contacted in the 50 states. In many instances, the initial contacts consulted others to gather the information requested in the survey. The questions asked were: 1) What is the estimated number or area equivalent of high tunnels in your state?; 2) What are the principal crops being grown in high tunnels in your state?; 3) What is the focus of research or demonstration work in your state that you are aware of? Responses were received from 46 states and are presented in Tables 1 and 2.
Estimated area, number and types of high tunnels, and predominant crops cultivated in them, as reported by state in the United States in 2007. Information was obtained through an informal survey of state extension vegetable specialists and other experts in each state.
High tunnel fruit, vegetable, and flower research, and demonstration activities reported by extension specialists and others by state in the United States in 2007. Selected references to previously published work are included by state.
Results and discussion
Table 1 lists estimates of high tunnel areas, numbers, and principal crops grown in them for states from which responses were received. Respondents were not consistent in their definition of high tunnels. Hence, some respondents included commercial flower production, nursery overwintering structures, or small heated greenhouses (e.g., Arizona, Rhode Island, and Vermont), while many reported tunnels used only for vegetable, fruit, and cut flower production by small acreage farmers. We included all responses received in the survey, but it should be understood that rather than presenting results that are strictly comparable from state to state, the responses are reflective of the high degree of variation in the number and use of high tunnels from state to state and of concomitant variation among states in awareness by extension workers of the current status of high tunnel use by growers in their state.
Most respondents reported that the numbers they provided were just their best guesses because there is currently no mechanism to accurately track high tunnel area, numbers, and crops in most states. The U.S. Department of Agriculture (USDA) census of agriculture does not distinguish between high tunnels and heated greenhouse structures (USDA, 2007). In our survey, some estimates of high tunnel area (e.g., Florida) seem high, but most estimates provided are probably conservative. We did not ask about the average size of operation, but the respondent from Illinois estimated this to be between one and four 2000-ft2, single-bay tunnels. The average size of operation for multi-bay operations would be larger (several states reported these) because these typically have a minimum size of 0.5 acre. Mechanisms for more accurately tracking high tunnel acreage, crops, and grower needs would be desirable.
While many crops were reported to be grown in high tunnels (Table 1), the widespread importance of some crops was noteworthy. For most states, tomato was among the first crops reported. High-tunnel tomato crops are typically ready to market earlier than the field-grown crop, and they typically produce a higher quality crop with fewer requirements for inputs (Blomgren and Frisch, 2007; Jett, 2004; Nennich et al., 2004). The extent to which high tunnels are used for fall and winter production of cool season leafy green vegetables is not entirely clear from Table 1, but this is likely an important component of production in many states of the continental United States, ranging from Michigan to New Mexico. The widespread reporting of cut flowers is noteworthy, as are reports of small fruit production from many states, affirming that these crops can be profitable in high tunnels (Heidenreich et al., 2008; Wien, 2009). High tunnels are amenable to large-scale production, with raspberry (Rubus spp.) production in California being the most striking example, but in most states, high tunnels are being used by relatively small-scale producers to serve local markets (Table 1).
Table 2 summarizes high tunnel vegetable, fruit, and flower research and extension activities reported by state. Again, the list is certainly not complete, but it indicates that horticultural researchers and extension personnel in many states reported conducting activities aimed at assessing the potential of high tunnels, of researching particular production systems or problems, or demonstrating the benefits of high tunnels. The large number of states with active or incipient programs, and the large number of crops and management topics being addressed are indicative of significant needs and opportunities for high tunnel research and extension around the country, and of funding opportunities to help support these efforts. Because high tunnels are unheated and passively cooled, crop selection and management will be determined by local environmental conditions. This, and the previous lack of research on high-tunnel production systems in the United States, provide a strong justification for broadly decentralized research and extension efforts.
Conclusions
From the results of the survey and literature cited, it is evident that producer interest in and adoption of high tunnels is high, and there is a wide variety of research and extension activities ongoing around the country. In most places, high tunnel fruit, vegetable, and flower production, and research and extension efforts are primarily geared toward responding to growing demand for fresh, locally grown produce. With the considerable environmental protection that high tunnels provide to crops, and with growing producer awareness of the advantages these structures provide, continued expansion of acreage and diversification of crops grown in high tunnels is likely in the United States. We can look forward to an expanding body of research and practical knowledge to meet the needs of producers.
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