rotect the glazing from
damage by UV light also prevent exposure of the crop to UV light.
Exposure to excessive UV radiation can slow growth or directly
damage many crops. However, exposure to sufficient UV light is needed to
encourage the plant to protect itself from radiation. The stronger cell walls,
changes in physiology and thicker, waxy cuticles that plants develop to protect
themselves from exposure to UV light also help protect them from pests and
diseases. Many plants also grow more compact when exposed to UV light. So, just
like grower-controlled exposure to natural breezes, careful exposure to UV
Á light can improve crop quality, reduce the use of chemicals and reduce
costs. Natural UV light is free, but you need a structure that lets you take
advantage of it.
For crops like bedding plants or perennials that will
eventually be used outdoors where they will be exposed to UV light, plants properly grown in open-roof structures are always acclimated to UV light. This
eliminates labor costs and growing space needed to relocate crops to a
“hardening-off” area before shipping.
Using full sunlight
All greenhouse glazings reduce the total amount of light
available to the crop. Stationary
coverings reduce the amount of light all the time, even when a reduction
(shading) is not needed. Under cloudy conditions or in the early morning and
late afternoon hours, shading is usually not needed. Open-roof structures
provide growers with the option to expose the crop to all of the available
light whenever shading is not needed. The extra light can influence crop
Compared to the taller, softer growth with weak stems that
some plants develop when grown in traditional greenhouses, careful exposure to
full-sun conditions when grown in open-roof structures encourages plants to
develop stronger stems, waxy surfaces and a compact growth habit. So, just like
grower-controlled exposure to natural breezes and UV-light, careful exposure to
full sunlight can improve crop quality, reduce the use of chemicals and reduce
costs. Natural, full sunlight is also free, but you need a structure that
allows you take advantage of it.
As is the case with UV light, for crops that will eventually
be used outdoors where they will be exposed to full sunlight, plants properly
grown in open-roof structures are already acclimated to full-sun conditions.
This eliminates labor costs and growing space needed to relocate crops to a
“hardening-off” area before shipping.
Optimizing natural DIF
Growers have been using DIF to manipulate plant growth for
many years. Reducing the difference between the day and night temperatures
helps many crops develop a compact growth habit. Open-roof structures can be
easily operated to keep temperatures warm at night and cool during the day
without the energy and maintenance expense of a cooling system, thereby
reducing the difference between the day and night temperature. The natural,
outdoor air temperature is free, but you need to have a structure that can take
advantage of it.
When open-roof structures are operated to reduce DIF
(maintaining cool daylight temperatures), the relationship between the amount of light the plant is exposed to each day (daily light integral) and the average daily temperature is altered. In traditional greenhouse systems, the temperature is controlled by the cooling system, but light levels remain unchanged. In
open-roof structures, crops receive more light when the roof is kept open to
release heat. When this “photo:thermal ratio” is increased, plants
accumulate more dry weight (more carbon) on a daily basis, which can lead to
faster growth or development. So, one way to obtain compact plants using DIF
and faster crop development at the same time is to operate the open-roof
structure to optimize the photo:thermal ratio.
Adapting to open-roof growing
When using open-roof structures, grower-regulated exposure
to natural breezes, natural UV light, natural full sunlight and DIF all
contribute to crops that are naturally compact, naturally more pest- and
disease-resistant and continuously acclimated to o