Cravo roof in a closed position.

Cravo roof in a closed position.


New protected orchard structures were installed last spring at Michigan State University’s horticultural research station at Clarksville. They were built over a 2010 planting of high-density sweet cherries and will be used in at least three research projects.

MSU cherry researcher Dr. Greg Lang said the new structures include a retractable-roof greenhouse that provides much more control over the environment than the high tunnel structures he has been working in, and also a vented row cover structure (the VOEN orchard covering system). Lang began research on growing cherries in protected environments in 2005.

Three sweet cherry research projects will be conducted in the new shelters, and another will involve raspberries.

One cherry project is the Specialty Crop Research Initiative-funded Solid Set Canopy Delivery spray system, in which fixed-in-place emitters are used to spray the fruit in what looks like a solid-set irrigation system set into rows of trees. Lang began working on the prototype of this system three years ago with cherries, using Haygrove high tunnels at the Southwest Michigan Research and Extension Center in Benton Harbor.

A second project is the NC-140 regional research trial comparing cherry training systems. Lang and collaborating researchers elsewhere across North America are studying the performance of sweet cherries grown in four high-efficiency training systems, including the KGB modified Spanish bush system, the Upright Fruiting Offshoot (UFO) system developed in Washington State, the tall spindle axe, and the slender spindle axe system developed in Italy.

A third project, funded by USDA’s Small Farm program, is evaluating the management and benefits of growing sweet cherries in various types of protected environments.

The new retractable roof structures were manufactured and donated to the university by Cravo Equipment Ltd. Called the X-Frame greenhouse, it has a strong interior ­structure and a computer-programmable retractable roof.

“The Cravos have significant advantages over the Haygroves, at the tradeoff of ‘you get what you pay for’ cost,” Lang said. “Retractable roof protective structures require a significantly higher investment than high tunnel structures, so additional crop value must be obtained. The VOEN system has a cost comparable to the high tunnels, but with a greater ability to vent heat in the summer at the tradeoff of less heat retention in the spring.”

One of the key reasons for putting sweet cherries under cover is to protect them from rain and thus control cracking during harvest, a major problem that has discouraged their production in the eastern United States and encouraged it in the desert climates of the West. Lang and other researchers have found that it’s not only rain that causes ­cracking as the cherries ripen, but groundwater or irrigation water as well.

In the new greenhouses, water is not only shed to the sides, it is captured in gutters and moved completely away from the growing trees.

The retractable roof is computer controlled based on an integrated weather station, making it very effective for research and for optimizing environmental control.

The retractable roof will be used during:

—early spring to manipulate flowering time and to help protect flowers from frost or freeze
—flowering to control temperatures and humidity levels for pollination
—the growing season to protect the trees from hail
—the growing season to reduce rain-disseminated diseases
—the summer to reduce losses from sunburn and prevent reduced fruit size caused from excessive transpiration
—preharvest to shelter fruit from rain
—harvest to keep the fruit cooler to maximize water content helping to extend the shelf life
—postharvest to create optimum growing conditions to help trees prepare for the ­following growing season

The goals of the trials under the retractable roof are to document the ability of the retractable roof to protect the crop from climatic risks, manipulate the timing of the ­harvests, and increase fruit size, quality and yield.

Cravo claims to be the world leader in retractable roof greenhouses and the retractable roof production system. The 30-year-old company is located in Brantford, Ontario, Canada, in the heart of a large greenhouse production industry. It has sales offices in Canada, Mexico, Spain, and Turkey, and sales around the world. Designs are available for heavy snow loads and high winds.