Greenhouse and Other Structures

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Chapter 19

• Greenhouse and Other Structures

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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.

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Detached A-frame Truss

• Is the most expensive to build and heat, but
  provides the best environment control.

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Quonset-style Greenhouse (hoop house)

• Requires new covering nearly every year.

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• 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.

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Eight common types of greenhouse Materials

• Glass
  Fiberglass

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• Soft-plastic Shade fabric
• Three different types of soft plastic
  polyethylene, vinyl, polyvinyl fluoride.

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• Polycarbonate rigid panels
• Acrylic rigid panels

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Hotbed a low growing structure that uses
electric cables or heating pipes to provide the
warmth needed to propagate, start, or harden off
plants.
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• 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.

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• 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

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Ventilation System

• Roof Side Exhaust Fans
• Retractable Roof Fan convection tube

oldest method of ventilation
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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.

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Two ways of providing shade in a greenhouse

• Externally- spraying on a compound
• Internally- Fabric or cloth suspended above crop
  to reduce light intensity.

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• 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.

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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.

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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.

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• 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

True
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• 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.

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Three functions a greenhouse must fulfill

• Must drain quickly
• Must be of a width that allows workers to reach
  into their center
• Must maximize the crops exposure to light

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• Tomatoes and lettuce require ground beds.
• Raised benches are used in the production of pot
  crops as well as cut flowers.

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• 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.

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• 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.

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Typical cross-bench arrangement

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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.