High tunnels are used extensively for fruit and vegetable production throughout Asia, Spain, and the Middle East, and more recently in the United States. This technology is also expanding in Canada, both in terms of the area devoted to high tunnel production and the variety of horticultural crops produced within.

High tunnel and field plot design at the GCUOF during peak of growing season. Photo Credit Mackenzie Plommer

What are High Tunnels? High tunnels are not greenhouses! Rather, they are a growing system that could be characterized as something between a row cover and a greenhouse, a simple frame over which transparent plastic sheeting is stretched. In contrast to row covers, high tunnels are sufficiently high to allow growers to walk through them and are less expensive to construct and maintain compared to greenhouses.

Why all the Hype? High tunnels offer many benefits similar to those of a traditional greenhouse but at a much lower cost. Though high tunnels do not offer the precise environmental control of a greenhouse, they sufficiently modify the environment to support early/late season crop growth. High tunnels also provide benefits of wind and rain protection, soil warming, insect control, and reduction of disease and predator damage. High tunnel production systems are becoming a more viable option for growing specialty crops, with the fixed costs of installation lowering as time goes on.  The cost of a standard-size high tunnel plastic and construction materials can range from $1.50-2.50 per square foot, compared to a typical range of $5-30 per square foot for conventional greenhouses.

High Tunnel Research.  Are high tunnels suited to Canadian climates for efficient production of high-value organic crops? The University of Guelph Centre for Urban Organic Farming (GCUOF), initiated a three-year research project in 2015 to address that question with support from the federally-funded Organic Science Cluster II (OSCII) (see below).

OSCII is a government and industry-supported research and development endeavour initiated by the Organic Agriculture Centre of Canada at the Dalhousie Agricultural Campus in Truro, Nova Scotia.  OSCII focuses on innovation and market development to ensure that Canadian organic growers have the resources they need to continue to capitalize on market opportunities.

The experiment is comparing the growth of tomatoes, bitter melons, and peas in high tunnels to those grown in the field. It aims to determine the most appropriate protocols for using high tunnel technologies in Southern Ontario to extend growing seasons, optimize nutrient and water use, reduce pests and increase profits for organic farmers producing high-value vegetable and nutraceutical crops.

The results will provide organic growers a scientific basis for choosing high tunnel designs, best practices for successful high tunnel crop production, and will demonstrate the feasibility of growing high-value crops organically in high tunnels in Ontario. The data being collected include microclimate conditions within the high tunnels throughout the growing season as well as yield data comparing high tunnel and field crops. Ventilation openings of three of the six high tunnels involved in the experiment have been covered with insect netting, to assess how this technique may decrease insect pressure, thereby reducing vectors for pathogen transmission on crops.

One season down, two to go. The first research year produced an abundance of interesting information. The favourable microclimate within high tunnels allowed for earlier planting and first harvest dates, leading to significant increases in fruit weight and fruit numbers as well as more frequent harvests, compared to that of open field plots (Table 1).

Damage from animals and adverse weather conditions such as hail severely impacted the field-grown peas, resulting in little harvestable crop. A large proportion of tomatoes grown in the field were completely lost due to disease, compared to high tunnel production, where disease incidence was relatively reduced, due to less moisture on leaves. Growth and yield of bitter melons and tomatoes was greater in the warmer, protected high tunnels. The average yield of bitter melons increased exponentially, moving from open field to high tunnels with netting (Table 2).

Large, fruitful bitter melons ready for harvest inside high tunnels. Photo Credit Yun Kong, Nora Alsafi

Insect monitoring. A significant reduction in insects was observed in high tunnels compared to field plots. High tunnels with exclusion netting resulted in even lower pest presence, averaging 9.76 insect counts per trap, compared to 42.6 in high tunnels without netting during the 2015 season. With the extended production period, better microclimate and reduced yield loss from disease, animals and severe weather, it is no surprise there were earlier and much more frequent harvest of crops grown in high tunnels compared to those in open field trials.

2016 research. The 2016 growing season will focus on examining the effects of fruit thinning on fruit ripening time, fruit quality traits and fruit yield of indeterminate cherry tomato under both high tunnel and open field conditions. Additionally, the effects of black and clear plastic mulch will be compared in terms of plant growth and crop yield of organic pea pods during early spring production, as well as their ability to suppress weed growth under high tunnel and field conditions.

Focusing on the implementation of insect exclusion netting for pest and disease control, a diversity of insect traps will be deployed to determine whether insects are causing damage to crops presently grown in high tunnel production systems as well as whether insect exclusion netting effects plant disease pressure. Results from this project will be used to develop Integrated Pest Management recommendations for both Canadian organic and conventional growers using high tunnel production systems.

A high quality tomato plant grown in high tunnels. Photo Credit Yun Kong, Nora Alsafi

Summary. The modified climate inside high tunnels creates an opportunity to diversify, producing crops that would not succeed if grown unprotected in our climate. By protecting crops from weather, pests and disease, high tunnels can help organic growers produce more types of top quality fruits and vegetables with viable yields.

Outside the regular growing season, high-value crops like tomatoes and peas cannot be successfully grown to consumer quality, but can be produced in high tunnels earlier in the spring and later into the fall. Extending the growing season offers tremendous opportunities for growers wanting to meet Canadian consumers’ demand for locally produced, organic fresh vegetables, fruit and flowers. High tunnels allow Canadian organic growers to produce crops outside of the normal growing season—increasing their profits and pleasing consumers—a win-win for both!