Article #3

Greenhouse Plastic

There was a time when greenhouses were expensive enough to build that only the wealthy could own one. Today, thanks to modern construction materials and especially to polyethylene plastic film, greenhouses have become much cheaper to build and are within the means of any homeowner willing to invest a small amount of money and a reasonable amount of work.

The benefits of growing plants in a greenhouse are extension of the growing season and protection of vulnerable crops from the elements. Greenhouses are often used to start plants from seed that cannot be grown in the open early enough in the year to do that.

The plants are either grown in the greenhouse from planting to harvest or, more commonly, transplanted to an outdoor garden once the danger of frost is past.
 

Building your own greenhouse is easy. The important "working" part of the greenhouse is the transparent material that admits direct sunlight through, but blocks longer-wavelength reflected light in the infrared. A greenhouse thus traps solar heat and maintains higher temperatures than plants would be exposed to if planted outside.

A small greenhouse suitable for growing plant starts from seeds can be made from polyethylene film attached to a wooden or metal frame, rather than from glass panels.

A larger or more durable greenhouse can be made from rigid plastic panels; these serve the same function but cost a bit more. Use of greenhouse plastic greatly reduces the cost of the greenhouse compared to using glass panels, and also saves on the cost of other materials necessary to frame and hold glass panels.
 

Greenhouse Plastic Film

Greenhouse plastic can be purchased in bulk and cut to fit. Greenhouse film is sold in spools intended for greenhouse use for roughly 10-12 cents per square foot. It can be ordered online or purchased in home-improvement stores such as Home Depot.

Usually, for online purchase a minimum quantity must be ordered. Some sources sell spools only, while others offer plastic film that is "cut to fit." A search for "greenhouse plastic film" will reveal many outlets for the purchase. Typical greenhouse plastic film is 4-6 ml thick polyethylene. 6 ml greenhouse plastic is more durable and, especially for larger greenhouses, is recommended. Spools of greenhouse plastic may be purchased in various widths from 16 inches to 48 inches and occasionally wider. Length of the plastic is cut to fit either by the source or by you.

 

Greenhouse Plastic Panels

Greenhouse plastic can also be purchased in rigid panels. This material is more durable than plastic film, but also more expensive. Typical costs run 70 cents per square foot and up. (The panels are not sold by the square foot but that's what the price comes down to.)

Besides cost, another disadvantage of panels over film is that they are less flexible in terms of greenhouse dimensions. You will need to explore what size and shape of panels are available and incorporate that information into your design. On the plus side, your greenhouse will be sturdier and less likely to develop damage from exposure to the elements.

Greenhouse Plastic From Home Depot

If you would prefer to see your materials before purchase and also avoid shipping costs, you can buy greenhouse plastic film or panels from Home Depot and similar home-improvement stores. The price is usually comparable to what can be found online. You can also buy complete greenhouse kits using plastic panels. As one might expect, the kits are more expensive than buying the plastic film and building your own. Greenhouse kits can be ordered online as well.