Growing Under Open Roofs
If someone told you that you could take advantage of optimal light, ventilation and natural DIF, saving on chemical and labor costs, what would you say? All it takes to get started is an investment in an open-roof greenhouse system.
What is the function of a growing structure? To control the environment or to assist the grower with manipulating healthy plant growth? Should the grower and the plants be forced to adapt to the environment the greenhouse provides, or should the greenhouse provide adaptable environments the grower needs to force the crop? Open-roof structures provide more environmental flexibility compared to traditional greenhouse designs.
Working With Nature
Greenhouses create a growing environment in response to the
outdoor environment. Heating systems are needed when the outdoor environment
makes the greenhouse too cold. Fans and cooling systems are needed when the
outdoor environment makes the greenhouse too hot (or perhaps the greenhouse
design provides insufficient ventilation). Shading systems are needed when the
outdoor environment provides too much radiation (too much light or heat).
Irrigation systems are needed since the greenhouse roof prevents natural
rainfall from watering the crop. Horizontal airflow fans are needed to
circulate the air because the greenhouse prevents exposure to natural breezes.
Supplemental lighting systems are needed when the outdoor environment provides
insufficient light (or perhaps the greenhouse glazing does not provide
sufficient light transmission). All of this technology is expensive and
requires energy and maintenance to operate.
Many cultivars that are healthy when grown outdoors may
stretch and become infested with pests and diseases when forced in a
greenhouse. Growers are forced to use chemical growth regulators and pesticides
to regulate height and control pests. If growers could use the outdoor
conditions that support the growth of healthy, high-quality plants when those
outdoor conditions are available, then growers might be able to reduce the use
of growth regulators and pesticides.
Just as there are beneficial insects useful for Á
biological manipulation of pests, there are “beneficial”
environmental conditions useful for manipulation of plant growth. Both are
helpful tools when used properly; both are a waste of money when not properly
The list of useful environmental conditions (see sidebar on
page 30) that are not available when growing in traditional greenhouse designs
is also the list of the advantages of growing under “open” roofs.
In open-roof structures, growers have more control over the development of stem
caliper, insect resistance, disease resistance, transplanting-stress resistance
and root growth development because they have more control of exposure to
natural breezes, exposure to natural UV light, exposure to full natural
sunlight and exposure to cooler daylight temperatures.
An often-repeated statement is: “Growers understand
that 80 percent of problems in a greenhouse can usually be traced to poor
environmental conditions.” By working with the natural environment as
much as possible, growers using open-roof structures can expose the crop to the
best available environment for a longer period of time.
During any crop-growing cycle, the best environmental conditions often occur outside a traditional greenhouse. Open-roof structures allow the grower to expose the crop to beneficial outdoor environments while retaining the ability to protect the crop from sub-optimal outdoor environments (without having to move the crop). The grower has greater control of crop development than can be obtained by growing in traditional greenhouses or outdoor compounds alone (or in combination). The risks associated with greenhouse-only or
outdoor-only growing are nearly eliminated.
Using the natural breeze
In traditional greenhouses, the solid roof and side walls
protect the plant from exposure to damaging winds. Stationary coverings also
prevent exposure to gentle, natural breezes. If the grower can expose the crop
to natural breezes, t