More growers are seeking out better technologies when it comes to retractable roofs, particularly more control over climate than what is offered with tunnels. The following advice is provided from Luis Gaxiola of Cravo Equipment.
In cold climates
Retractable roofs are used in a cold climate to allow the maximum amount of sun energy possible. By opening the roof when temperatures are not too low, it allows the plants to invigorate growth and help reduce moisture problems.
"The ability to retract the roof when outdoor conditions are optimal, allows plants to receive more light and warm up faster from being exposed to direct sunlight," Gaxiola said. "The combination of more light, lower humidity and wind helps dry off the plants to increase the rate of water loss which helps increase flower development, increase fruit size and BRIX. Drying off the leaves will also help reduce the risk of foliar disease."
The roof can then be closed to protect berry crops from cold temperatures, when they are present. "If temperatures are low and these represent a risk to the crop, the roof can then be closed," he added. "For the cover, we use a transparent plastic roof, which produces a greenhouse effect and can remain completely closed to protect the berries, resulting in a greenhouse effect.
In hot climates
For berry growers located in warmer areas, Gaxiola said the retractable roof will also aid in maximizing production. He also recommended using a white roof to reflect away strong sunlight. "When growing in hot climates, a retractable white cooling roof will allow growers who are targeting winter production to transplant weeks earlier, allowing them to harvest earlier before open field production comes into focus," he said. "The white roof can also be closed at night during the winter to help increase production by keeping plants warmer at night. Growers can then also use the white cooling roof to help extend the season in the springtime when the excessive heat causes and end to open field production and conventional tunnel production. A low pressure mist system will also help reduce plant stress during the hot dry conditions.
The roof can be retracted and closed as appropriate to keep temperature and humidity levels more consistent. "The roof can be retracted when temperatures are lower than ideal for the crop," Gaxiola continued. "Then, when this temperature is exceeded the roof can be closed 90% to protect the crop from high levels of radiation. Additionally, a high pressure sprinkler system can be installed to keep the relative humidity conditions at optimum for the crop. For these projects a white plastic is used to give a shade effect to the crop."
A stand-alone greenhouse offers almost complete protection from wind and rain. With a retractable roof, this option naturally remains. The retractable roofs are fitted with both a rain sensor and a barometric pressure sensor, which work together, triggering the roof to close automatically should a rain event occur.
"In rainy conditions, the greenhouse is equipped with a weather station that helps to anticipate closing the greenhouse completely before the rain starts to fall thus avoiding any damage to the crop," Gaxiola shared. "For the cultivation of strawberries, the model with a waterproof roof is suggested."
According to Gaxiola, the retractable roofs manufactured by Cravo have never suffered damage from wind or hail, even in hurricane conditions. "Retractable roof houses have proven to be extremely resistant to damage from wind since they have been hit by 18 hurricanes without the loss of any structures," he said. "In addition, the retractable roof covering has a usable life of typically 8-12 years. During that time, roofs have never blown off and have proven to be very resistant to hail as well. For regions of strong winds, retractable roof greenhouses have walls 5 meters high, which serves as a physical barrier of protection."
Cost and usage
In regards to installation costs, Gaxiola said that, just like any investment, the calculation of returns is vital. He argued that the additional production means retractable roof greenhouses pay for themselves after 3-5 years.
"Retractable roof houses are more expensive than a conventional tunnel and less expensive than a glass house," he stated. "When targeting the high price windows, the return on investment can be 3-5 years. This technology allows for the optimal density of planting, allows plants to develop their maximum reproductive potential, allows for earlier and later harvests to enter the best price windows; these all ensure a return of the investment in a shorter time frame."