How to Stretch Greenhouse Plastic? A Step By Step Guide


Unlike polycarbonate or glass panels, greenhouse plastic (polyethylene) needs to be stretched and attached to the greenhouse’s frame. It needs to be pulled tight to prevent the wind from blowing it around and possibly ripping and tearing it apart.

Many homeowners prefer to use greenhouse plastic because it is inexpensive and easy enough to install. But even though it might be easy to install, stretching the film is a bit more intricate. So, how do you stretch greenhouse plastic?

  1. Pull the wire to take the slack off the plastic.
  2. Start in the middle of each side and work outward. Pull tight as you go along and use the fold lines in the plastic to keep it square.
  3. Repeat step 2 on the other side of the greenhouse.
  4. Use snap clamps to attach the plastic to the frame.
  5. Two people can make this job a lot simpler. One person pulls and the other secures.

If you are about to install your first greenhouse with greenhouse plastic and are unsure of how to stretch it tightly, then you have come to the right place. This article will guide you step by step, from preparing the frame to installing and stretching the plastic and creating a ventilation system.

How Do You Stretch Greenhouse Plastic?

Polyethylene is a flexible, lightweight plastic that is used to cover the structure of a greenhouse. The plastic is easy to install, energy-efficient, inexpensive. Like glass or polycarbonate panels, polyethylene can also be penetrated by the sun’s rays and offers protection from elements such as rain and wind.

It is very durable and can last up to three growing seasons. When you are about to start the process of covering your greenhouse with polyethylene greenhouse plastic, it is important to get as many people as you can to help you with this tricky task.

Choose a day with little to no wind to prevent the plastic from blowing away by a strong gust of wind.

Before you stretch the plastic, you first need to install it onto the greenhouse structure. The steps to install the greenhouse plastic are as follows;

Here’s a quick install video to get started with more info below:

Prepare The Frame

The frame of the greenhouse must be smooth and free of any abrasions. Whether the structure is made of metal, plastic, or wood, you can use white tape foam to smoothen the surface or sand it smooth. A smooth frame prevents excessive wear and tear to the greenhouse plastic.

Installation

Step 1

Set your greenhouse plastic roll up on one end of the greenhouse.

Step 2

Fold the ends and tie a firm knot around the nub a few times to ensure it is secured properly. Fold the plastic back on itself and this time tie a knot around the underside of the nub to create a smoother “pulling handle” to pull the greenhouse plastic across the top of the greenhouse.

Step 3

Run the rope (tied around the nub) across the greenhouse structure, all the way to the other end.

Step 4

The person standing at the end where the plastic roll is can start to take pressure off the plastic so that the person on the nub end can start pulling the plastic over the center on top of the greenhouse tunnel. This allows the plastic to unfold to the right and left sides of the structure in equal lengths.

Step 5

Continue pulling the plastic across the entire length of the structure, all the way to the other end of the structure’s top center.

Step 6

Next, the person pulling the plastic must remain near the peak and hold the plastic in place as the other person drops one side of the plastic to the ground.

Step 7

Install a temporary spring wire under the hip rail on each end of the greenhouse structure.

Step 8

Do the same with the other side and make sure the spring wire holds the right and left sides securely in place.

Step 9

It would be best if you worked from the center peak toward the hip rail at the bottom of each end, and the person on the other end must mirror you.

Step 10

Repeat step 9 on the other end of the greenhouse (from the peak to the hip rail).

Step 11

In the center of each side, start working toward the ends and finally end the wire at the end of the hip rail.

Helpful Hint

Be careful when you install polyethylene film if your greenhouse structure is made from PVC pipe. PVC pipes emit gasses that can deteriorate the polyethylene plastic prematurely if they are in direct contact. There are various ways to prevent the two materials from touching each other such as;

  • Where the plastic meets the PVC, apply a layer of polyethylene tape.
  • Use old pieces of polyethylene plastic to wrap around the PVC pipe where the two meet before you install the new plastic. The old layer protects the new film from deteriorating.
  • Use white acrylic latex paint to paint the PVC pipe. This forms a protective layer between the plastic and the PVC pipe. It would be best if you avoided any paint containing fungicide or mildew-resistant additives.

Here’s a more in depth video to install greenhouse plastic with more info on stretching the plastic below:

Stretching The Greenhouse Plastic

Now that you have installed the plastic over the whole structure, it is time to stretch and secure it tightly.

If your plastic is secured tightly, it won’t move too much when the wind blows, reducing wear and tear to the plastic, and reduces the stress placed on the high tunnel’s frame. Installing your greenhouse plastic in warm weather ensures that the top cover won’t be loose. The following steps will guide you through stretching your greenhouse plastic;

Step 1

Starting at the peak ends of the greenhouse structure, pull ahead the wire to take the slack off the plastic.

Step 2

By working outward in the center of each side. Using broad downward pressure prevents white streaks in the plastic from forming as you apply pressure (using your forearm). You can make use of the fold line in the plastic to ensure that it is square.

Step 3

Do the same on the other side (starting in the middle of each side and working it to the opposite end side).

Step 4

Once you are done installing your spring wire, you can move on to installing the roll-up sides (for ventilation). Spring wire and spring wire channels are the most effective ways to attach your greenhouse plastic to the high tunnel of the greenhouse.

*Anti-drip greenhouse plastic is a great low-cost greenhouse plastic to use.

For very large greenhouses, it is recommended that you tie ropes to each corner of the plastic and throw them over the entire structure. Grab hold of the ropes and pull the plastic over the greenhouse.

Ensure that the plastic is equal lengths on both sides. Check up regularly to ensure that the plastic is still tightly in place, especially when there have been cold and warm days following each other. If you find that the plastic is a bit too loose, you may have to consider re-stretching it.

Ventilation – Roll-up Sides

Now that you are done stretching the greenhouse plastic, you need to create a ventilation system. One of the most affordable methods is rolling up the greenhouse plastic on the sides when it comes to ventilation.

This method works on hoop houses and high tunnels and eliminates the need for using power (electricity) operated ventilation. All you need is some basic hardware. A roll-up side is made up of hardware components such as;

A Gearbox Or Handle

A gearbox or a handle is used to operate a roll-up side. It allows the roll bar to move up and down. A gearbox is used mainly in larger structures, while smaller and shorter high tunnels, hoop houses, or greenhouses only require a handle to operate its roll-ups. Gearboxes or handles are used to crank up the tunnel easier. 

 A Roll Bar

Without a roll bar, a roll-up side cannot function. To install a roll bar, you need 1315” in galvanized steel tubes and should extend slightly past each end of the structure using pan head screws to attach the roll bars. Pan head screws are light and do not add too much pressure on the plastic while operating roll-up sides.

Hip Rail

A hip rail attaches to each bow it touches and runs the length of the entire structure at the level of your chest or hip. The structures roll-up sides run down from the hip rail to the ground. Hip rails are usually made from materials such as aluminum or wood (lumber). If your hip rail is made from lumber, you need to attach a single spring wire channel to it. Aluminum hip rails use double-channel spring wire (optional/recommended).

Snap Clamps

The most cost-effective way to attach the greenhouse plastic to your roll bar is by using snap clamps. Snap the clamps over the plastic onto the roll bar. Snap clams are available in various sizes, with the one that fits over 1315” bars being the most widely used.

Baseboards (Optional Not Needed)

While not technically needed, a baseboard is ideal for preventing the roll-up side from resting directly on the ground.

Anti-Billow Hardware

Anti-Billow hardware stops the wind blowing the sides around, which can cause severe damage to the structure. It consists of rope and fittings that attach to the rope, holding the roll bar securely in place.

Greenhouse Plastic (Polyethylene Film)

There are various types of greenhouse plastic available to use for roll upsides. The most widely used is single covered, cut to a long enough size for covering the roll upsides. Greenhouse plastic variations have different levels of lifespan durability and light transmission.

How To Install Roll-Up Sides

  1. Assemble the roll bar.
  2. Install a gearbox or handle on the roll bar depending on the size of the structure).
  3. Cover the structure with greenhouse plastic.
  4. Attach the greenhouse plastic to the roll bar.
  5. Test the roll bar to see if it operates properly and adjust if necessary.
  6. Attach the greenhouse plastic to the roll bar permanently.
  7. Install the Anti-Billow hardware.

Here’s a video showing another approach to securing the plastic on a greenhouse:

How Tight Should Greenhouse Plastic Be?

Greenhouse plastic (polyethylene) contracts and expands with the climate. In warm temperatures, the plastic will expand, and in lower, cooler temperatures, the film contracts.

Stretching your greenhouse plastic to make it tighter is necessary; however, overstretching the film could cause it to start tearing and, finally, ripping apart on cool days. After you have installed the greenhouse plastic, pull it down to increase the tension on the plastic.

When you are happy with the taut, use drywall screws to anchor the film to the baseboards. These screws are great because they are easily removable when it’s time to re-stretch the greenhouse plastic.

Position the plastic in between the baseboard and the aluminum stripping. Allow about 1 to 2 feet of the polyethylene film to extend past the baseboard around the entire greenhouse structure.

Use soil to cover the extra plastic on the ground, and if you need to re-stretch the plastic, this overhang makes it possible.

Please Note: Only pull greenhouse plastic tight enough to prevent water from accumulating and until there are no more creases or wrinkles. The plastic itself should not stretch. Otherwise, it will tear while contracting as temperatures start to drop, especially if you have overstretched it on a warm day.

In Conclusion

Though it might seem like a strenuous task, stretching your greenhouse plastic is vital to the whole setup. The last thing you want is to see your greenhouse plastic flopping around, tearing and damaging all the hard work you have put in to make the greenhouse, not to mention the damage to your plants and crops.

It is also to keep the structure from breaking as the wind jerks the plastic about. Eventually, the tension on the frame will become too extreme, and you may end up having to start over from scratch, wasting time and money.

If you still feel unsure, there is no harm in asking the assistance of a professional or someone who has stretched greenhouse plastic before.

Robert Sampson

I'm Robert Sampson and I live in Colorado where I spend a lot of time in the backyard with my family either grilling, playing games and sports, or working on a project to make our backyard a better place to be.

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