Lucas Greenhouses in Monroeville, N.J., finishes a lot of plants outside. The company operates 25 acres of heated production space and more than 30 acres of outdoor growing area.
Prior to putting up a 211,000-square-foot Nexus “Convertible” retractable roof greenhouse three years ago, the company was finishing nearly 1 million square feet of spring plants outdoors between April and June.
“The reason we ended up with a retractable roof structure is because we finish a lot of plant material outside in the spring,” says head grower Joe Moore. “We start moving plants outside sooner than we should. We were doing a lot of 4½-inch vegetative calibrachoas and petunias, which are cold tolerant. If it was raining and orders had to be pulled from outside, the efficiencies weren’t where I wanted them to be. I wanted a structure that would mimic outdoor growing conditions by providing high light levels and good airflow and would give me the ability to have temperature control and also offer wind and rain protection.”
Moore says initially he tried to improve efficiencies on the 4½-inch crop by staging them in a standard greenhouse with flood floors.
“We weren’t able to achieve the same airflow on the greenhouse crops that we were getting on the crops grown outside,” he says. “We didn’t get the same plant toning in the greenhouse that we got outside.”
More Sophisticated Structure
According to Moore, the retractable roof structure Lucas Greenhouses built is more like a traditional greenhouse.
“Most retractable roof structures don’t have the sophistication that this one has,” he says. “This structure has heated concrete floors with flood floor irrigation. The only difference between our retractable roof structure and our high-dollar end greenhouses is the roof itself. There is no glass on the retractable roof structure. Our Nexus open-roof glass greenhouse has vents located above the gutter that tend to damper the air movement. With the retractable roof greenhouse, the cloth-covering accordions to a full open position so it provides the same conditions as growing outside but with some protection.”
Spring plants are usually moved into the retractable roof structure during the last week of February at Lucas Greenhouses.
“There is still a chance that we can get snow at that time,” Moore says. “We know we are pushing the envelope in terms of getting the crops in the house earlier than most growers. We have increased the heating capacity of the house in order to be able to melt the snow. Because the structure doesn’t have the same snow-load capacity as a standard greenhouse, we have to be able to generate enough heat to melt the snow to keep the structure from coming down. The house is not super tight and there is only a single layer of cloth covering it.”
The structure has been equipped with Lennox forced-air heating units that were installed this past year. The heaters were mounted on the gable ends of the greenhouse. In the middle of the house where heater exhausts couldn’t easily be run up through the retractable curtain, Holland Heaters direct-fired units were installed.
“There is no exhaust on them, and they burn very cleanly to eliminate any harmful gas emissions inside the house,” Moore says. “They’re our Stage 3 heating system. They are the last heaters to come on when temperatures are bitterly cold or if we need to melt snow quickly. We have added several million Btu of heat with the additional heaters. We had 12 fairly significant snow storms this year, so we feel the additional heaters were a worthwhile investment.”
Moore says he initially thought the heated concrete floors would generate an adequate amount of heat to melt the snow that fell on the covering.
“Most growers using retractable roofs don’t have concrete floor heating,” he says. “They don’t have to be concerned about freezing in-floor heating tubes if they blow out water lines and turn the heat off in their retractable roof structures. They will just open the roof and let the snow fall inside.
“We wanted to be able to operate the house like a traditional greenhouse. If a grower expects to operate a retractable roof house when it snows, he is going to spend more on fuel in order to melt the snow. If a grower isn’t able to supply adequate heat and keeps the roof closed then he can lose the structure to snow load collapse.”
Structure Benefits, Limitations
Growers need to be aware that growing in a retractable roof structure is different than a traditional hard cover greenhouse, Moore says.
“There are going to be more leaks,” he says. “It’s not as water tight. It’s not going to be as efficient on heat as a standard greenhouse. We also installed a heat retention curtain under the retractable roof cover, which is used at night to save on fuel.”
Plants are grown in the Lucas retractable roof structure until early November.
“All of our summer crops are grown in the structure because it creates a better environment during the summer,” Moore says. “All of our fall pansies are grown in it. Also, our 6-inch garden mums are grown in the structure rather than outside where they can fall over easily.”
Moore says being able to provide direct sunlight and better airflow results in better toned and hardier plants. Nexus polycarbonate drop-down EDDG vents were installed on three sides of the structure to assist with cross ventilation.
“We have tried to run crops through some greenhouses that didn’t get the same effect as the crops grown in the retractable roof structure. This house has also lessened the need for plant growth regulators, and there is less disease and insect pressure. The plants are toned and tougher.”