New greenhouses are built for the first crop that will be grown in them. Most greenhouses are designed for heated cultivation and prepared for limited snow loads. In a greenhouse for warm crops, the gutters and cover rods are lighter, and that does not suffice with a heavy snow load.
Technical specialist Theo Herngreen sees that entrepreneurs are currently switching more often from warm to cold cultivation. The high price of gas is one of the causes of this crop switch. "The entrepreneurs making the switch are not always aware of the consequences for their greenhouse. If snow falls on a greenhouse in which no heating is used, that greenhouse has to be made stronger. I advise entrepreneurs to keep themselves well informed and ask their greenhouse builder, installer, or technical specialists from Interpolis. It is a necessary investment to maintain your business."
From peppers to strawberries or from roses to hydrangeas
When a crop switch is going to happen, entrepreneurs energetically set about preparing their greenhouse for the new product, but that is not enough. Theo tells of his experience with entrepreneurs who switched from roses or peppers to hydrangeas or strawberries.
"For the new crop, much less heating is needed. One entrepreneur had his gas connection reduced. Another one had it cut off. The entrepreneurs were not aware that they'd have a problem in the winter. The greenhouse is not strong enough to hold snow. That snow cannot be shed and there is a chance that the greenhouse could collapse due to the weight. Also, the greenhouses were not resistant to frost. Even at 4 degrees, the vents can freeze solid and glass can break due to meltwater left behind."
Theo says also that "a greenhouse originally built for warm cultivation is prepared for a snow load of 25 kg per m2. We take into account that the temperature just below the greenhouse roof always stays above 12 degrees. The design takes into account that the greenhouse is heated in the winter. This determines the bearing capacity. A greenhouse built for cold cultivation is prepared for 42.3 kg per m2. These greenhouses are built stronger. Ask your greenhouse builder for an estimate of the bearing capacity of cover and glass. That way you will know how much snow your greenhouse roof can take."
From warm to cold cultivation?
When switching from warm to cold cultivation, almost no unheated greenhouse can withstand snow pressure. Theo gives the following tips on behalf of Interpolis:
- Keep the original heating system and make sure you have enough boiler capacity. Then you can melt snow away from the cover.
- Keep the gas contract that allows you to keep the temperature under your greenhouse roof at least at 12 degrees in the winter. It can then be turned on when the conditions require it.
- If necessary, install an additional heating pipe under the gutter. This will help you melt snow faster and easier.
- Before buying a greenhouse or when switching crops, have your greenhouse builder, structural engineer, installer, or technical specialist from Interpolis inform you of the possibilities. They can determine whether your greenhouse is strong enough for your new crop and whether you can shed enough snow.
Not necessarily much more expensive
Entrepreneurs switch crops more often during the lifetime of their greenhouse, or they are using their greenhouse for longer than it was designed for. Theo, therefore, advises investing in the future-proofing of a greenhouse by giving it a heavier build. A greenhouse that is suitable for both cold and warm crops is the best solution. The difference in investment is only 1 to 2% of the purchase price. "By giving a greenhouse a heavier build, it becomes stronger and you can prevent many problems. The investment is also easily returned because there is no need to heat the greenhouse when it snows."
Source of text and photo: Interpolis