Greenhouse plastic

I've just wrapped a bunch of tomato cages with 3.5mil plastic sheeting to create green tepees for my tomatoes. The sheeting is opaque not clear because that's all that Home Depot had (it's sold in the paint department not the garden department). Is there special greenhouse plastic sheeting that would work significantly better or is the drop cloth plastic good enough? I'm only going to be using the green tepees until the end of May.
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They allow for ventilation? You may want to put clear plastic on the soil to warm it up as well.
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- Billy

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On Mon, 09 May 2011 12:10:20 -0700, Billy wrote:

The tepees are open at the top so it should be ventilated well enough. I'm just trying to get an early start, the normal time to plant tomatoes around here is the end of May, doing it at the start of May is a little risky. I'll remove the tents in a couple of weeks when the weather becomes more reliable.
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I think plastic is enough to cover the greenhouse. It does not need any special plastic.
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lisaray

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On Fri, 27 May 2011 07:52:19 +0000, lisaray

it depends on how long you want it to last.
D
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Depending on the plastic, the frost protection factor associated with a row cover can vary from 2? to 7? F. Generally the heavier materials (spunbonded polypropylene) give greater frost protection but tend to exclude more light.
Greenhouse coverings include long-life glass, fiberglass, rigid double-wall plastics, and film plastics with 1- to 3-year lifespans. The type of frame and cover must be matched correctly.
Glass. Glass is the traditional covering. It has a pleasing appearance, is inexpensive to maintain, and has a high degree of permanency. An aluminum frame with a glass covering provides a maintenance-free, weather-tight structure that minimizes heat costs and retains humidity. Glass is available in many forms that would be suitable with almost any style or architecture. Tempered glass is frequently used because it is two or three times stronger than regular glass. Small prefabricated glass greenhouses are available for do-it-yourself installation, but most should be built by the manufacturer because they can be difficult to construct.
The disadvantages of glass are that it is easily broken, is initially expensive to build, and requires must better frame construction than fiberglass or plastic. A good foundation is required, and the frames must be strong and must fit well together to support heavy, rigid glass. Fiberglass. Fiberglass is lightweight, strong, and practically hailproof. A good grade of fiberglass should be used because poor grades discolor and reduce light penetration. Use only clear, transparent, or translucent grades for greenhouse construction. Tedlar-coated fiberglass lasts 15 to 20 years. The resin covering the glass fibers will eventually wear off, allowing dirt to be retained by exposed fibers. A new coat of resin is needed after 10 to 15 years. Light penetration is initially as good as glass but can drop off considerably over time with poor grades of fiberglass.
Double-wall plastic. Rigid double-layer plastic sheets of acrylic or polycarbonate are available to give long-life, heat-saving covers. These covers have two layers of rigid plastic separated by webs. The double-layer material retains more heat, so energy savings of 30 percent are common. The acrylic is a long-life, nonyellowing material; the polycarbonate normally yellows faster, but usually is protected by a UV-inhibitor coating on the exposed surface. Both materials carry warranties for 10 years on their light transmission qualities. Both can be used on curved surfaces; the polycarbonate material can be curved the most. As a general rule, each layer reduces light by about 10 percent. About 80 percent of the light filters through double-layer plastic, compared with 90 percent for glass.
Film plastic. Film-plastic coverings are available in several grades of quality and several different materials. Generally, these are replaced more frequently than other covers. Structural costs are very low because the frame can be lighter and plastic film is inexpensive. Light transmission of these film-plastic coverings is comparable to glass. The films are made of polyethylene (PE), polyvinyl chloride (PVC), copolymers, and other materials. A utility grade of PE that will last about a year is available at local hardware stores. Commercial greenhouse grade PE has ultraviolet inhibitors in it to protect against ultraviolet rays; it lasts 12 to 18 months. Copolymers last 2 to 3 years. New additives have allowed the manufacture of film plastics that block and reflect radiated heat back into the greenhouse, as does glass which helps reduce heating costs. PVC or vinyl film costs two to five times as much as PE but lasts as long as five years. However, it is available only in sheets four to six feet wide. It attracts dust from the air, so it must be washed occasionally.
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- Billy

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