The Pros and Cons of Greenhouse Coverings

greenhouse_typesGreenhouses can be covered in one of three materials.  This includes glass, polycarbonate, and plastic film.  Each one of these materials has pros and cons associated with it.  So before you decide on a certain greenhouse structure or shape, consider the covering.

All coverings should go through a checklist that includes cost, ease of repair, durability, weight, how much light goes through the material and how much heat is released through the material.

Glass Paned Greenhouse

The Large Royal Victorian Greenhouse sold by Outdora is an excellent example of a glass paned greenhouse.  This type of greenhouse covering is durable, has low maintenance cost, absorbs photosynthetically active radiation (PAR) easily, releases excess heat during the night and has a low transmission rate of UV light.

But while glass pane greenhouse have many positives, there does exist some negatives.  The first is the fact that glass breaks.  Hail, tree branches and vandalism can break the panes.  Secondly, if the greenhouse is very tall, then the replacement of these panes may not be a simple matter.  Third, water that is used in the greenhouse can etch the glass, making it less productive.

Polycarbonate Paned Greenhouse

An example of this type of greenhouse covering can be found on the Snap and Grow Silver Greenhouse.  The polycarbonate is more durable than the plastic film and does a pretty good job of holding heat.  When this first type of covering is initially used, it does a good job of absorbing the photosynthetically active radiation (PAR), but over time the efficiency of this product decreases.

The negativity to this covering is two-fold.  First, the cost of replacement panels can be very expensive and finding the size can be a challenge.  The second problem is created by water and fertilizer, which just like glass can etch the surface of the panel and make it less effective.

Plastic Film Covered Greenhouse

The plastic film that is used to cover row crops is also used to cover greenhouses.  This type of covering can be found on Outdora’s Hot House Greenhouse.  This type of covering is very flexible, inexpensive and can have pigment added to it to increase yield or ward off pests.  An example of how this works is simple.  An additive is added to the plastic that excludes ultra violet light (UV) and creates a chemical free type of pest control or a glossy finish is added to repel insects.  Production can be increased by simply impregnating with color pigments to increase the absorption of a certain wavelength and, in doing so, increasing production.  Producing a white plastic that reflects sunlight can also regulate greenhouse temperatures.  While this may seem counterproductive, it is a way of preventing the plants inside the greenhouse from burning up.

Surfactants can also be added to the plastic to reduce surface tension of water, in doing so eliminating condensation buildup.  Antistatic chemicals are another addition that can be added and reduce dust build-up on the surface of the plastic.

Both water droplets and dust can affect the plastic film’s ability to properly absorb sunlight by 8 percent.  Having the ability to include these additives has made plastic film an important covering for greenhouses.

The negative to plastic film is the fact that it needs to be replaced often and more often than one may think.  If you choose a greenhouse with this type of covering, plan to replace the plastic long before it shows wear.  Doing this will keep your greenhouse performing to its maximum with minimum down time.

A greenhouse can be an expensive purchase, but choosing one with the correct cover will make the experience a more rewarding one.

Mindy McIntosh-Shetter has been an Agricultural Science educator, and is a horticulture and/or environmental blogger who earned a degree from Purdue University in Agriculture Education with a minor in biology, and natural resources. Presently she is finishing up her Masters in Environmental Education and Urban Planning for the University of Louisville while working on her own agriculture/environmental blog.

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