Chapter_19_Hort

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Transcript Chapter_19_Hort

Chapter 19
Greenhouse and Other
Structures
Three main purposes of greenhouse
structure:
To provide a controlled growing
environment for plants whose economic
value justifies the expense.
 To permit the growth of plants in regions
where survival outdoors is not possible.
 To extend the season of growth for plants
at times when they would normally go
dormant.

Detached A-frame Truss

Is the most expensive to build and heat,
but provides the best environment control.
Quonset-style Greenhouse
(hoop house)

Requires new covering nearly every year.
Traditionally people mostly
used plastic to cover
greenhouses since it was
cheaper than glass, but
because of the recent rise in
cost of all petroleum-based
products, plastic and fiberglass
now rival glass in initial cost.
Eight common types of greenhouse
Materials
Glass
Fiberglass
Soft-plastic*
Shade fabric
* Three different types of soft plastic: polyethylene, vinyl,
polyvinyl fluoride.
Polycarbonate rigid panels
Acrylic rigid panels
Hotbed:
a low growing structure that uses
electric cables or heating pipes to
provide the warmth needed to
propagate, start, or harden off plants.

Cold Frame- a low growing structure that
uses the heat of sunlight passing through
glass or plastic to provide the warmth
needed to propagate, start, or harden off
plants.

Why is the need for supplemental heating
apparent in a greenhouse?
– A greenhouse lacks the ability to retain
sufficient heat after the sun sets.
Nearly all greenhouse systems are
automated now, and many involve both
primary and back-up (emergency)
systems.
 The even distribution of air throughout the
greenhouse is essential for consistent
temperatures and uniform plant growth.
 Greenhouse air should move slightly as
often to minimize mildew and other
diseases of plants that proliferate under
stagnant conditions

Ventilation System
Roof & Side*
Exhaust Fans
Retractable Roof
Fan & convection tube
* oldest method of ventilation
Three basic approaches taken with a
greenhouse depending on time of year,
and geographic location:

Shading the glass to reduce light intensity.

Ventilating to allow cooler outside air to
replace warm air inside.

Promoting heat exchange through water
evaporation.
Two ways of providing shade in
a greenhouse:
 Externally-
 Internally-
spraying on a compound
Fabric or cloth suspended
above crop to reduce light intensity.
Greenhouse ventilation systems bring
fresh air into the greenhouse to replace
the warm internal air.
 Especially during hot weather, ventilation
alone is not enough to cool a greenhouse.
 Both fan and pad cooling and fog
evaporative cooling systems can reduce
greenhouse temperatures from 10
degrees to 30 degrees F below the outside
air.

Cooling:
Fan and pad - Uses exhaust fans and
continuously wet pads of excelsior (a fibrous
porous material) cross fluted cellulose,
aluminum fibers, or glass fibers. Cools through a
re-circulating water system.
 Fog evaporative- Uses a high pressure pump to
create a fine mist. As the fog disperses through
the greenhouse, the evaporation causes desired
cooling without wetting plants.

Greenhouse and Energy
Conservation
Greenhouse management has shown an
orientation of crop types to geographic
regions. Crops needing higher
temperatures are being grown more in
southern states than in northern ones and
vice versa. They are also constantly trying
new conservation techniques.
The principle disadvantage of adding an
extra layer of plastic to an existing
greenhouse is the reduction of light
intensity.
 True or False: Large amounts of heat are
lost through the concrete or wooden sides
of the greenhouse?
 After Dark:

– When most heat is lost in greenhouse
– When fuel consumption is greatest

Automated blanket systems have been
developed for greenhouses because they
can be set on timers.

The focus of conserving energy has
caused the greenhouse industry to enter
into a period of change.

The style of benches, materials used, and
arrangements within the greenhouse
depend upon the crop being grown.
Three functions a greenhouse must
fulfill
 Must
drain quickly
 Must
be of a width that allows
workers to reach into their center
 Must
light
maximize the crops exposure to

Tomatoes and lettuce require ground beds.

Raised benches are used in the production of
pot crops as well as cut flowers.
Raising the bed above the ground allows
air to flow more freely around the crop
and permits a warmer root-zone
temperature to be maintained.
 A framework of pipe constructed above a
regular bench allows for hanging baskets
to be grown above another crop.

The most important quality of a bench is
its capacity for rapid drainage.
 Any wood used in the construction of
greenhouse benches should be preserved
with some type of preservative.
 One determines the number and width of
aisles within a greenhouse by finding the
width of the carts needed in the aisles,
and whether the crop can be worked from
one side or needs to be accessible from
both.

Typical cross-bench arrangement
Different types of bench
arrangements:
Cross-bench arrangement-aisles along the sides
and between the benches, is least efficient use
of space for growing.
 Peninsular benching- features a wide central
aisle to accommodate carts and other
equipment. The narrow aisles between benches
allow access by workers and efficient space for
growing.
 Length-of-house- utilizes growing space
efficiently, but workers must walk the length of
the house to get to the other side of the bench.
