How to Pick a Tarp for Your Greenhouse DIY Project

Growing things and creating plant life is a joy.

It gets your hands dirty, and literally helps you reap what you sow, but some of the gardening zones in the United States can make it difficult to grow what you want, when you want.

If you’ve been reading up on how greenhouses operate, then you know you need to let the right nutrients from the sun touch your plants while controlling the temperature and humidity.

A greenhouse tarp is the final piece of the puzzle. Most of us don’t have the option to commission every individual glass pane for an expensive greenhouse (otherwise we wouldn’t have gone the DIY route).

Instead, it’s time to figure out what tarp you need to get the same results for a more reasonable cost.

What Kind of Tarps Are Used in Greenhouses?

Polyethylene is the only tarp that you can effectively use in a greenhouse.

One of the key things about greenhouses is that they don’t allow moisture in or out, and tarps that consist of mesh are designed to allow some levels of moisture out. Polyethylene is your best choice for a host of reasons.

UV Rays

Polyethylene blocks most UV rays, but still allows enough light in to properly nourish your plant life. If you use a clear polyethylene tarp, you’ll give your plants the proper amount of sunlight to ensure they grow as needed.

Moisture Protection

No moisture comes in or out. This allows you to maintain the perfect humidity levels inside your greenhouse, which is especially helpful for those cold winter months when you have to heat the place. If you want to maintain your greenhouse year-round, this is the perfect material.

Heat Transference

Glass panes in traditional greenhouses are better at letting the heat in than they are at keeping it out. With a greenhouse made with poly tarps, you still get a bit of heat that comes through from the light, but not as much. You have a better layer of protection against temperature changes.

Heat transference happens when cold air touches the outside of a glass pane and seeps through it to then affect the warm air touching the other side of the pane. We want as little heat transference as possible to maintain a consistent ecosystem indoors.

Inexpensive

Poly tarps, even 14 mil clear tarps, are always going to be cheaper than getting glass panes. By an extreme amount. If you’re making a DIY greenhouse, it’s probably because it’s a much cheaper option.

On top of that, there’s a lot less load bearing weight than glass panes, so you can use a lighter frame for your greenhouse out of PVC or something similar. You should still secure it to the ground/attach it to a house or barn, but it’s a way to cut down on all the costs.

What Type of Tarp Lets the Sun Through?

A clear polyethylene tarp at 14 mils will allow enough sunlight to enter, but not allow the rain to come through. It’s very important that it sticks to those specifications.

14 mils is the perfect thickness to ensure rain isn’t going to come through. Some tarps can be thin enough that they’re only rated for a few years before they break, but 14 mils is basically the perfect medium.

It keeps costs low, it lets in the right amount of light, and it’s still lightweight enough to make this a fairly easy task for you.

Do not use tarps with a fabric on the inside of the lining. That means no insulated tarps, no cotton canvas, none of that. You need that direct transfer of light if you want a successful greenhouse.

How to Make Your Own DIY Greenhouse

Most of this is going to consist of building the frame, so be ready for bonding PVC T brackets together and having a fun time with that.

1. Decide on a Size

The great thing about doing this yourself is that you get to choose how much room you get by selecting the dimensions.

You can go nuts with this and make it the same size as an inground pool if you wanted to (10’ x 20’), or just make it a simple, small, walk-in greenhouse for container gardening. The choice is yours.

2. Sourcing

Once you have your dimensions set, you have to build a frame out of PVC pipe.

It would be a good idea to use the same thickness of PVC throughout the entire build just so everything is cohesive at the end. It’s cheap, so get a little bit extra to account for mishits when you’re cutting it so size.

3. Base Frame

Start from the ground up. You want to make a rectangle out of PVC pipe, connecting the corners with elbow T brackets so you can run the walls without any problem.

To get the most out of this, build the frame around whatever large containers you have in here so you don’t have to haul them in later.

4. Corners

You’ve decided how tall your greenhouse is going to be, so it’s time to put the corners in. Your corners are important, which is why the taller you want your greenhouse to be, the thicker you need your PVC pipe to be.

Slip your PVC pipes into place and make sure they’re going up nice and straight. Use a level if you need to make sure.

5. Top Elbow Brackets

At the top, place more elbow T brackets that go horizontally. You want to run the pipes along the top to create a cube out of this entire thing. Don’t worry about the door frame, or lack thereof. We’re going to cover that.

6. The Roof

Now comes the hard part: the roof. You have to make this separate and then hoist it up on top. Thankfully, it’s not going to be too heavy, so you should be able to handle it on your own.

Create another base frame like you did before, but this time, you’re going to need brackets that allow you to place it on top of those corner poles and allow you to create a slight angled roof on top.

Cut your roof PVC pipes at a 45° angle so that they meet in the middle, and attach to a center PVC pipe that runs the length of the steeple.

7. Drape the Tarp Over Your Greenhouse

Put the roof on top of the greenhouse and secure it into place. Drape your tarp over it, and see where it needs to be adjusted.

You want it to come all the way down to the floor so it can attach to the corner poles, and comfortably drape over the top of the roof. Cut the tarp to fit, and affix it to the roof with ball bungees.

8. Create the Backing

Now you need to make the back end of the greenhouse.

Using the tarp you have left, measure and cut a piece that will fit in place and create a complete cover. Attach this with ball bungees or sew it into place is you have the aptitude, creating a backing to the greenhouse. One more step.

9. Front Door

Repeat number eight, but instead of sewing it into place, we need to make a door out of it. You can simply sew one half of a zipper onto the outline of your door piece, and the other half into place on the edge of the roof tarp piece.

Feed the zipper in and close this as needed. You only have to unzip this halfway to gain access into the greenhouse.

How Long do Greenhouse Tarps Last?

The whole point is that they’re extremely exposed to the elements and provide the perfect enclosure for your greenhouse. With all that weather-related stress, you’re putting these tarps through the ringer.

It all depends, and you should only replace individual tarps as needed (if you’re using multiple tarps like big window panes on your greenhouse frame), but on average you can expect one tarp to last for three to five years.

Hopefully, they can last longer than that, but it’s hard to tell because we don’t know what conditions this greenhouse is going to have to face. Are you prone to hurricanes or nor’easters? Is it excessively dry where you are?

There are many different ways that a tarp can degrade over time, and chief among them are rain and excessive dry heat/UV rays.

Let the Sunshine Through

You need the nutrients from the sun to nourish your plants, which is why the right tarp is an absolute necessity. Now that you know all of the attributes that help your greenhouse plants actually thrive, it’s time to select your tarps and get them fitted to the right size.

Browse our selections to find the perfect tarp for your greenhouse DIY project.