Chapter 19 Greenhouse and Other Structures Three main

Chapter 19 Greenhouse and Other Structures

Three main purposes of greenhouse structure: n To provide a controlled growing environment for plants whose economic value justifies the expense. n To permit the growth of plants in regions where survival outdoors is not possible. n To extend the season of growth for plants at times when they would normally go dormant.

Detached A-frame Truss n Is the most expensive to build and heat, but provides the best environment control.

Quonset-style Greenhouse (hoop house) n 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.

n 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. n Why is the need for supplemental heating apparent in a greenhouse? – A greenhouse lacks the ability to retain sufficient heat after the sun sets.

n Nearly all greenhouse systems are automated now, and many involve both primary and back-up (emergency) systems. n The even distribution of air throughout the greenhouse is essential for consistent temperatures and uniform plant growth. n 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: n Shading the glass to reduce light intensity. n Ventilating to allow cooler outside air to replace warm air inside. n Promoting heat exchange through water evaporation.

Two ways of providing shade in a greenhouse: n Externallyn Internally- spraying on a compound Fabric or cloth suspended above crop to reduce light intensity.

n Greenhouse ventilation systems bring fresh air into the greenhouse to replace the warm internal air. n Especially during hot weather, ventilation alone is not enough to cool a greenhouse. n 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 recirculating water system. n 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. n

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.

n The principle disadvantage of adding an extra layer of plastic to an existing greenhouse is the reduction of light intensity. n True or False: Large amounts of heat are lost through the concrete or wooden sides of the greenhouse? n After Dark: – When most heat is lost in greenhouse – When fuel consumption is greatest

n Automated blanket systems have been developed for greenhouses because they can be set on timers. n The focus of conserving energy has caused the greenhouse industry to enter into a period of change. n The style of benches, materials used, and arrangements within the greenhouse depend upon the crop being grown.

Three functions a greenhouse must fulfill n Must drain quickly n Must be of a width that allows workers to reach into their center n Must light maximize the crops exposure to

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

n 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. n A framework of pipe constructed above a regular bench allows for hanging baskets to be grown above another crop.

n The most important quality of a bench is its capacity for rapid drainage. n Any wood used in the construction of greenhouse benches should be preserved with some type of preservative. n 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. n 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. n 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. n