By Tom Lee

There are many choices in choosing a greenhouse but the main factors you have to consider are:
1. the amount of space you are going to need
2. the amount of capital for investment
3. training
4. the type of business
5. environmental requirements
6. market
7. labor requirements and
8. personal preferences.

 
Other factors in choosing a greenhouse is the building site:
1. good drainage
2. accessibility
3. available utilities and
4. amount of sun exposure.

 
Design of the greenhouse must be:
• minimal in size to permit maximum light into the greenhouse for the crops while still supporting itself
• heating and ventilating units and
• the weight of the crop which is trained to grow up a support system carried by the greenhouse frame.

 

 
 
 

Green house covers:

• Glass is the most common cover: it reduces the shading of the crop from the support frame.  Shading may seem minimal in greenhouses but it is estimated that 1% decrease in light would mean a 1% decrease in yield.

 
• 3 types of grades of glass include
1. A Grade used for households
2. B Grade used for store windows, greenhouses
3. C Grade not so good
 
• Disadvantages of using glass include:
1. inflexible
2. heavy
3. expensive and
4. easily damaged by hail.
 
• Advantages include:
 
• permits high level light radiation into the greenhouse and
• durable.
 
• Polyethylene sheet film: was developed in England in 1938.  Since it was invented it is used worldwide because it is easy to work with and inexpensive.
• Different types of polyethylene film include.
1. regular
1. thickness is 4 mill to 6 mill
2. cost is 100 dollars per sheet.or 2.5 cents per square feet.
3. Disadvantages include high thermal emittance and UV degradation
4. advantages include inexpensive, good for air insulate structure, keeps greenhouse humidity high and reduces heating costs by 35% to 40%.
2. uv resistant polythylene
1. thickness is 6 mill
2. cost is 4 cent per square feet
3. advantages include resistant to UV light, air inflated structures and greenhouse humidity
4. disadvantages include priced higher than regular.

 

 
 
 
 
 

• Polyvinyl chloride (PVC): mainly used in Japan in 1950's
1. thickness is 8 mill-12mill
2. cost is 20 cents per square feet.
3. advantages include soft and pliable
4. disadvantages include electrical static collects dust, reduction of light transfer and the sheet turns yellow in 18-24 months

 

 
 
 

• There are many other coverings including:
• polyvinyl fluoride
1. advantages include UV resistant
2. disadvantage include brittle in winter and tearing at nail holes.
• rigid plastic pvc
1. disadvantage is that it turns black
• plexiglass
1. advantages include low thermal transmission, good light transmission and high weather resistant.
2. disadvantages include scratches and expensive
• acrylic panels (Exolite)
1. advantages include durability, reduction in heating costs and very pleasant appearance
2. disadvantage is expensive
• lexan
1. advantages include: resistant to hail damage, heat retention is good and light transmission.

Disadvantage is very expensive.
Types of Greenhouses:
• Quonset
1. advantages include simple structure, fast to construct, can use plastic covering, air inflation can be used and clear obstruction
2. Disadvantage is low side walls.
 
• this is an example of a ridge and furrow green house.
1. Some advantages include costs less, less heating costs, more space utilization
2. Disadvantages include high snow load, temp control  is difficult
 
 
 
 
 
 
References:

NDSU Horticulture professor Dr. Lee Notes from GreenHouse production management class

Growing tomatoes hydroponically web site.
Green house builders