Resource Book on Horticulture Nursery Management

exposed wall area through which heat can escape. Heating pipes are usually located
beneath the gutters for this purpose.
Quonset-style Greenhouse
It is less expensive and can be purchased prefabricated or can be fabricated on the
site. The trusses are constructed from water pipe that is bent to fit 180 0 are modified for
some-what more vertical sides. In a Quonset style greenhouse uses pipes which are 6
meter wide, 1.5 cm in diameter. One inch diameter pipe is used for a 30 foot wide
greenhouse. Slightly larger pipe is driven into the ground into which the pipe arches are
inserted for support. A 5 x 20 sq. cm wooden plant is attached to the base of the pipe
arches such that it runs along the ground partially buried. This provides a basal point of
attachment for the plastic film. The pipe arches or trusses are supported by pipe purling
running the length of the house. Trusses are spaced 75 to 90 cm apart. The width of
plastic film required to cover a Quonset greenhouse of given width can vary according to
the height and shape of the trusses. A 6 meter wide greenhouse generally requires a 9
meter wide sheet of plastic. The covering width for a 30 foot wide Quonset greenhouse
varies greatly; the more common width is 12 meter. These green houses are either
constructed in a freestanding style or may be arranged in an interlocking ridge-andfurrow
manner. In this latter case, the trusses overlap sufficiently to place a bed of plants
between the overlapping portions of adjacent houses. A single large interior thus exists
for a set of houses, an arrangement that is better adapted to the movement of labor and to
automation.
Gutter Connected Greenhouse
This is the second currently popular plastic film greenhouse design. The gutters
can be placed at greater heights than is possible in ridge and furrow Quonset ranges.
Gutters, depending upon the manufacturer can range between 3 to 10 meter intervals.
Columns can be placed in greenhouses with gutters spaced 12 feet apart and the columns
placed under each, every other or every third gutter. Nine meter spacing between rows of
columns though expensive, greatly enhances the ease with which the shading of plants
with black cloth can be accomplished. Gutter connected greenhouses greatly minimize
the exposed surface area and consequently the heating cost. Only 6 meter of plastic film
is required to span a 5 meter bay. Gutter-connected bays of 3, 5, 7, 8, and 9 meter widths
can be covered by plastic film sheets 4, 6, 8, 10 and 12 meter wide respectively. When
additions are made, the plastic film can be removed from an existing side wall and the
new houses connected at that point without any resulting discontinuity. In this way, a
modest initial investment, inadaptable for automation, can be developed through
expansions into a structure well suited to automation. The gutter-connected greenhouse
brings us full circle to the category of permanent metal-frame greenhouses of which the
glass greenhouse is a member.
Greenhouse with Double-Layer Covering
All plastic film greenhouses make use of the air-inflated system. Two layers of
plastic film, one applied directly on top or the other from the outside, are held apart by a
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