By Guest Author Sean Barker.
What is a polytunnel?
A polytunnel is a greenhouse-like, semi-circular structure made with sturdy steel, PVC, or wood frames. They are covered with durable plastic sheets usually made of polythene (hence the “poly”) and can be constructed in a variety of widths and lengths. Gardeners use small polytunnels to extend the growing seasons of fruits, vegetables, and other plants, to protect plants from extreme weather, and to grow plants they couldn’t otherwise grow in their climate. On farms, they’re also used for housing animals and storing equipment – people have even been known to use them as plane hangars!
Why should you use a polytunnel?
There are plenty of benefits a polytunnel offers to gardeners of all skill levels.
- Longer growing season – Polytunnels can potentially extend the growing season by 6 weeks at either end. This means you can grow your favorite fruits and vegetables earlier or later in the season.
- Bigger crops – Crops grown in polytunnels have the potential to be bigger than crops grown in an open garden.
- Perfect for starting crops – Even if you prefer to grow your crops in open soil, a polytunnel can be perfect for getting seedlings started in a temperature controlled, safe environment.
- Protection from pests – They offer a vital layer of protection that keeps seedlings safe from hungry birds, squirrels, deer, and other wildlife.
- Protection from heat and environment control – You can control all aspects of the growing environment, including temperature, humidity and ventilation.
- Convenient construction – They are quicker to construct than permanent structures, and they can be designed to your exact size specifications.
- Adaptability – They are relatively easy to extend, move, and adapt to changing needs.
- Value for money – They are cheaper to construct and maintain than greenhouses – on average, polytunnels have a lower cost per square meter.
What can you grow in a polytunnel?
Practically anything! The only plants we would recommend not using a polytunnel for are fruit trees (which may outgrow the tunnel) and plants with thorns, as these could damage the cover.
Getting started
The easiest way to get started in polytunnel gardening is to build your own, small polytunnel. If you only have a small space or aren’t ready to make the commitment yet, you can get ‘mini polytunnels’. A mini polytunnel is a 4-foot wide tunnel that requires minimal assembly and maintenance but offers most of the same benefits as a full-size polytunnel. You can use these to protect new crops while they are in the seedling stage or to protect spring crops from frost.
How to build your own polytunnel
If you’ve decided to build your own polytunnel, it’s important that you know how to do it properly. Many people choose to take on building their own polytunnel as a DIY project as it’s the perfect activity for a sunny, dry weekend. If you aren’t too sure of your DIY skills, you can hire professionals to do it for you.
What you’ll need
The most reliable way of building a polytunnel is to purchase a kit online. A kit contains everything you need and materials that are optimized for growing plants. Try to enlist the help of 3 or 4 friends to help you build it.
Materials
A reliable polytunnel kit includes:
- Aluminium, PVC or steel framework and fittings
- Foundations – you can get different options for soil, concrete and timber, depending on where you are building it
- Timber or aluminium base rail
- Door frame/s
- Door/s
- Polythene sheet/cover
- Ventilation
- Anti-hotspot tape
- Additional extras such as crop bars and support braces for hanging baskets, or suspending canes and crops inside your tunnel
Tools
- Shovel
- Sharp knife
- Wood saw
- Battery operated drill
- Screwdriver
- Wrench set
- String line
- Spirit level
- Marker pen
Preparing the ground
Choose an area that’s level, sturdy, and dry.
- Check the weather. You should set aside 2 dry days to build your polytunnel.
- Decide where to build. Choose an area that will leave around 3 feet of space around the polytunnel
- Clear the area. Level the ground and clear away any leaves, weeds and debris.
- Mark out the site with string and stakes.
- If needed, lay a cement foundation for your polytunnel. This is usually not necessary for small tunnels.
Assembling the frame
The frame is the ‘hooped’ structure that makes up the inside of the polytunnel.
- Put together each hoop, carefully following any manufacturers instructions. Ensure you get the right fittings on each hoop to avoid any issues down the line.
- Add the completed hoops to the supplied ground tubes.
- Assemble the ridge pole – this is the pole that runs down the center at the top of the polytunnel. Connect all of the hoops together using the pole. You should have a rigid structure by now.
- Add any bracing that was supplied with your polytunnel and any crop bars.
- Apply anti-hotspot tape to areas of the frame which will touch the cover – this will prevent overheating and cover damage.
Covering the frame
Covering your polytunnel frame is where your team of helpers will really come in handy. The more people there are, the easier it will be to maintain the tension of the polythene sheet as you secure it in place.
There are two ways to secure a polytunnel sheet – either by adding a base rail to secure it (usually included in a polytunnel kit upon request) or digging a trench to bury the edges of the cover under the soil. Generally, base rails are used on harder ground, while a trench can be dug in soil.
- Unfold your polythene cover and shake it out.
- Carefully pull the polytunnel across the erected frame, taking time to make sure it is evenly distributing on all sides.
- Affix the cover to your base rail, or bury the edges in the trench, being careful to maintain tension.
- Once your cover is secured, you will need to cut the cover so that you can add your door frame/s and door/s.
Finishing touches
- Once the structure is completed, add the door rail, timber door frames, and hang the doors.
- Trim any excess from the polythene cover and tidy it up.
- If needed, add tension to the cover by raising the hoops (if you dug a trench) or adjusting the base rail.
Polytunnel FAQs
Many polytunnel growers choose to grow in containers or raised beds, whatever you prefer.
They can last anywhere up to 15-20 years if properly maintained, but you do need to replace the polythene cover every few years as wear and tear will occur.
If you’re new to polytunnels, start small. A tunnel with a 6-foot width is usually best.
The polytunnel is a versatile and economical option for protecting your produce from the elements. If you build one, be sure to follow the guidelines above, and enjoy the freedom of trying different growing methods and crop variations that the extended growing season provides.
Author’s Bio: Sean Barker is the managing director of First Tunnels, the UK’s leading supplier of both ‘domestic’ and ‘commercial’ polytunnels.
How do you heat this in the winter in Minnesota
Nancy: Here’s an article that may help: https://www.firsttunnels.co.uk/page/heating-a-polytunnel