Horticulture Magazine

How To Build Your Own DIY Polytunnel Greenhouse

a homemade polytunnel greenhouse

Polytunnel greenhouses offer some unique benefits, which is why they’re becoming more popular with gardeners.

Polytunnel greenhouses, or ‘polytunnels’ as they’re often called, offer a fantastic alternative to a traditional greenhouse. Having your own polytunnel will give you a more controlled growing environment for your plants and enable you to protect them from the harsh winter weather.

Another great benefit of having a polytunnel is that it will give you the opportunity to grow a range of plants and vegetables that wouldn’t flourish if were to try and grow them outdoors. With a polytunnel, you’ll be able to grow things like tomatoes, cucumbers, peppers and melons.

In this guide, we’ll be covering how to construct your own polytunnel as well as offering some tips on how to look it after once it’s completed.

Let’s gets started… 

What you’ll need

There are two main parts to a polytunnel – the frame and the polythene cover that will go over it. For the frame you’ll want to use metal tubing – aluminium is an excellent choice.

You’ll be able to get the metal tubes needed as well as the polythene covering from any reputable DIY store. There are also websites that sell polytunnel kits that include everything you need.

In addition to the frame and covering materials, you’ll also need the following –

  • A hammer
  • Spanners
  • Screwdrivers
  • A cordless drill
  • Timber for the door frames
  • Anti-hot spot tape

Constructing the frame

The first step to building a polytunnel is to lay the foundations. Before putting down any foundations, you’ll need to level out the soil. It’s a good idea to do this in the spring or autumn since the soil will be softer and easier to work with.

After the soil is level, you should bury the foundation tubes into the ground. This is what the aluminium hoops that make up the frame will be attached to. To keep the tubes in place, you attach a base plate to each foundation tube and then bury them until only the top of the tubes are visible.

Note: It’s extremely important that you make sure the foundation tubes are correctly positioned and lined up with each other. If you don’t do this, then it’ll become obvious when you try to add the aluminium hoops. 

Once the foundation tubes are in the ground you can then add the aluminium hoops, which are usually attached to each other using p clips. After all the hoops are in place, you should then add the centre rail to help stabilize the structure. The sidebars should then be added between each of the hoops to provide further stability.

Constructing the doors and door frames

After you’ve finished erecting the main structure of the polytunnel, you then need to add the door frames. Door frames are an extremely important part of the construction since they not only add support to the structure, but the cover will be attached to them too.

You’ll need to construct the door frames yourself. Once you’ve made sure the frames are properly aligned, you can put each of the posts into the ground and attach the other end to the frame using a p clip. Once the frames are in place, you’ll then need to build the doors themselves.

It’s a good idea to build 2-panel doors. This way you can cover the top half of them with netting, which helps with ventilation. The bottom half can be covered with polythene like the rest of the polytunnel. After the doors are constructed, you then simply attach them to the frames.  

After this, you have the option to build a base rail around the bottom of the frame. This is recommended since you’ll be able to attach the covering to it.

Applying the cover

Now that the frame is constructed, it’s time to apply the polythene cover. Before applying the cover, you should cover any parts of the frame that will come into contact with it in anti-hot spot tape. This is basically a type of insulation tape that will stop the metal from getting too hot in the sun and causing the polythene to rip.

When applying the cover, you want to ensure that it’s pulled very tightly over the frame so it provides good support to the structure and will also prevent water from collecting on the roof when it rains. To achieve this, you can either bury it into the ground or nail it into the wooden base rail if you built one.  

It’s highly recommended that you get a second person to help when applying the cover since getting the required level of tautness won’t be easy on your own.

Polytunnel maintenance

Although polytunnels are fairly low maintenance, there are certain steps you should take to ensure your polytunnel stays in the best shape possible.

Repair any damaged covering

If there are any rips in the polythene cover of your polytunnel, then you should repair them immediately, no matter how minor. If you ignore them, they can become much worse very quickly, especially during the winter when storms are common.

Wash the cover

Over time, the covering of your polytunnel can easily become dirty, which can prevent light from being able to get through and harm the health of your plants.

This being the case – you should clean the cover of your polytunnel thoroughly, both inside and out when you notice it getting dirty. The ideal time to do this would be in autumn since your plants will get less light over the coming winter months.

Another benefit of cleaning the cover of your polytunnel is that it will help to prevent disease.

Keep the interior clean

For the plants in your polytunnel to flourish, you’ll want to provide the best conditions for them possible. It’s very easy for a polytunnel to become cluttered over time and this can attract rodents so you should be sure to keep your polytunnel as clean as possible to avoid this problem.

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