Many gardeners attach polythene to a greenhouse frame because it is a very inexpensive glazing material. In addition, poly coverings are a safe and easy greenhouse covering for the average do-it-yourself gardener to work with compared to other materials. Properly attaching polythene to your greenhouse frame ensures that you'll get the most satisfactory use out of it before the time comes to perform maintenance or replace the frame's polythene covering entirely.
The most common materials used for covering greenhouses are fibreglass, polycarbonate, glass panels and polythene plastic sheeting. Plastic sheeting is less durable than the other materials, therefore, the covering must be replaced more often. However, it is also less expensive.
Two of the desirable attributes of plastic sheeting are its excellent insulation properties and its safety factor, since it can't shatter like glass panels. Polythene is commonly used by large commercial establishments to cover their vast facilities. A good-quality poly covering is 6mm thick and provides protection against ultraviolet rays. You can purchase greenhouse polythene that is guaranteed for at least 4 years before requiring replacement.
If you purchase a greenhouse kit, the best way to attach polythene to the frame is to use the mechanism usually included in the kit. For example, some hoop-style greenhouses have a method that involves securing flexible channels with clips inserted along the skeleton or frame. Remove the clips from the channel, fit the polythene into the groove and reinsert the clips. Another method uses a simple aluminium clamping system to secure the poly covering at various intervals along the frame.
Some people construct their own small, quick and easy DIY greenhouses; PVC is a popular choice for the frames and the hoop method of construction is a prime option. Once you complete the structure, spread plastic sheeting over the entire frame, extending it down to the ground with several extra inches of material.
Secure 2-by-2-inch strips around the plastic and the bottom framing perimeter; the framing is usually 4-by-4-inch lumber. Next, fold the plastic up over the 4-by-4 board, covering the staples or nails. Fasten the folded plastic sheeting to the 2-by-2 strip with another round of staples. This is also the method to use for greenhouses framed out of other materials, such as wood and metal.
Install the poly covering during the morning hours, before the sun heats up. This way, you're less likely to overstretch the material. Try not to stretch the film when installing it on warm days, as this weakens the covering. Avoid placing the material on the ground to prevent rips and tears in the plastic sheeting. This also eliminates the possibility of ground contaminants adhering to the covering. Slope the poly covering to ensure water run-off.