ble 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, the crop develops a compact appearance with stronger stems.
The response is similar to the use of “brushing” or
“mechanical conditioning” for height control. Proper operation of
open roofs and roll-up side walls lets growers capture natural breezes as a
growing tool to develop crops with strong stems and a compact appearance.
Exposure to gentle breezes has also been shown to help the
plant develop its own natural resistance to insects and diseases. It also
encourages proper development of waxy surfaces on leaves and stems, which help
reduce water loss and provide some protection against insect feeding and
invasion by germinating disease spores. When the plant’s own defenses are
stimulated, the effectiveness of biological predators is improved. So, compared
to structures with stationary coverings, plants grown in open-roof structures
often require fewer applications of pesticides. Natural breezes are free, but
you need a structure that lets you take advantage of them.
Naturally compact plants with strong stems and improved
resistance to pests let the grower reduce or eliminate the applications of
chemical growth regulators and pesticides. This reduces all costs and risks
associated with chemical applications, including: cost of chemicals,
application labor, application equipment maintenance, application
record-keeping, possible phytotoxicity damage to the crop, and possible worker
exposure to chemicals (including possible litigation costs). When your records
prove you have reduced your use of chemicals, you can also request a lower
premium on your liability insurance.
For crops like bedding plants or perennials that will
eventually be used outdoors where they will be exposed to natural breezes,
plants properly grown in open-roof structures are already acclimated to wind.
This eliminates the labor costs and growing space needed to relocate the plants
to a “hardening-off” area before shipping.
Using UV light
Greenhouse glazing greatly reduces or nearly eliminates
exposure of the crop to UV light. The materials that p