l, 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 outdoor conditions. These
growing tools may be used all at the same time or whenever one or more is
Compared to traditional growing structures, the timing and
concentration of growth regulators needed when growing in open-roof designs are
different. In some situations, they may no longer be needed. Similarly, the
timing and amounts of pesticides, fertilizers and irrigation water also differ.
Temperature recipes used to schedule crops differ. When growers switch to
open-roof structures, they will have to carefully reapply their skills to
manipulate crops as necessary. However, they will have many more tools and
alternatives available to them to help them be successful and profitable.
A computer operation system is an essential component for
proper operation of an open-roof growing system. Trying to keep the roof and
side walls in the correct position by hand is a full-time job, and other chores
will usually cause the person in charge of the structure to “fail”
on a regular basis. A one-time purchase of a good computer control system
(typically about $20,000 purchased and installed) is much less expensive than a
permanent, full-time worker.
No matter how sophisticated, growing structures do not
operate by themselves. Remember that the computer controller does not operate
the system or grow the crop for you. This is computer-assisted growing, not
computer-controlled growing. You must still know your crop and its needs, and
make daily, routine or seasonal adjustments to the computer settings as needed.
Consider the labor savings
An important reason growers are selecting open-roof
structures is to reduce labor costs. There are significant labor savings from
reduced crop handling. When using open-roof systems, plants need not be moved
from stationary-roof systems into “acclimation areas” for
hardening-off before shipping (the roof is moved instead). style="mso-spacerun: yes"> Useful growing space is not wasted as
Seasonal greenhouse glazings need not be removed — the
roof is moved instead. Eliminating each labor-handlin