How to Choose the Best Polytunnel for an Allotment
Polytunnels are affordable, easy to set up and make it far easier to grow a range of plants and produce.
They can act in a similar way to a greenhouse, keeping temperatures up and humidity high, allowing plants from different climates (or seasons) to grow comfortably. They can also protect plants from wind damage, insects and frost, depending on the style you go for.
Although polytunnels can be used in the garden, they are often seen on allotments due to their large size. Nevertheless, there are polytunnels that are suitable for smaller spaces.
In order to find the best polytunnel for an allotment or vegetable patch, you’ll need to consider the space you have available, your budget, and the results you want to achieve. The following information should help you make an informed decision.
Benefits of a Polytunnel for an Allotment
There’s a number of reasons why so many people opt to erect a polytunnel in their allotment.
- Warmer growing environment. Polytunnels are noticeably warmer than the outdoors, especially on sunny days. The warmer temperatures mean you’ll be able to grow crops you wouldn’t normally be able to in the UK, and you can also grow year-round with the use of a heater. In winter, polytunnels can help protect plants from frost.
- Longer growing season. On sunny days, your polytunnels will warm up quickly. This is especially noticeable in spring and autumn, where the sun still shines but the air stays a little chilly. Sunny days will warm your polytunnel, extending the growing season.
- Controlled environment. The climate inside a polytunnel is far easier to control than the climate outside. You’ll be able to control the temperature to some extent, and there’s less risk of rain, wind or frost damaging your plants.
- More cost effective than greenhouses. Opting for a polytunnel over a greenhouse should work out a lot cheaper. Polytunnels can also be erected on soil bases, and they are relatively easy to put together.
- Range of sizes. Polytunnels come in a huge range of sizes, so whether your allotment is large or small, you should be able to find a model to suit.
- No planning permission required. Like greenhouses, polytunnels don’t require planning permission. This makes them far less time consuming to set up than other outdoor structures.
- Portability. Polytunnels can be moved around the allotment or garden if needed. They are generally very lightweight.
- Protects plants from insects, birds and animals. Polytunnels also protect your produce and plants from the wildlife that comes into your garden.
Choosing the Right Size
Polytunnels come in many different sizes.
If you’re after more of a greenhouse feel, opt for a walk-in polytunnel with an internal height of around 2 metres. With one of these models, you can walk around inside the structure and tend to your plants without having to stoop. This also allows you to grow more plants. Some tomato plants can grow to around 2 metres.
If you lack space in your garden or your allotment is only small, a polytunnel that’s closer to the ground will feel less intrusive. There are smaller polytunnels available that are less than 50 cm high but can offer protection to specific plants.
In terms of length, polytunnels can range from around 3 metres long to upwards of 20 m. You’ll need to leave space around the polytunnel to erect it and carry out maintenance. Also, if using heaters, it will be easier to maintain the temperature of smaller polytunnels. Therefore, you may benefit from using several smaller polytunnels as opposed to one large one. This is also true as different plants may require different conditions.
Selecting the Right Cover Material
The covers of polytunnels can be made from a range of materials. Different materials will offer different properties.
Many polytunnels are made from polythene plastic. There are various types:
This allows a lot of light inside the tunnel, allowing plants to benefit from the full spectrum of light that they require. It can be useful in countries like the UK, because plants here can struggle to get enough light as it is – you may not want to block any more of it with a polytunnel.
It does not offer a lot of heat protection and therefore is best used in summer, not in winter. Some crops will not appreciate so much direct light.
- Polythene with an infrared additive
This type of plastic cover doesn’t let heat escape quickly through the cover. Therefore, it is good to use if heating the polytunnel, because the heat will remain trapped.
It’s useful for any plants that require a warmer environment.
These polytunnel covers are slightly more opaque and do not allow as much light in. They create shady conditions inside the polytunnel which are suitable for shade-loving plants.
Green polythene absorbs a lot of the red-light spectrum. As a result, it’s particularly beneficial for plants which thrive in green-light spectrum conditions.
Fleece is particularly good at insulating plants and keeping them protected from frost. It’s used for smaller polytunnels and also keeps bugs and birds away from specific plants. Some people choose to use fleece inside of larger polytunnels in order to protect their plants that way.
Different styles of polytunnel are available depending on your needs. The following features may be worth looking out for:
Polytunnels can either have doors made from the same material as the rest of the tunnel, or framed, structured doors. They may simply be flap openings, or slightly more sophisticated zip-lock doors. The better the door closes, and the less gaps that it leaves, the more insulated the polytunnel will be. Structured doors will only feature on more expensive polytunnels.
Zip doors can also work well, but the zips don’t tend to be very robust. They can break easily.
One of the main benefits of having a polytunnel is being able to control the environment that your plants and produce are growing in.
While polytunnels are loved for their warmth, they can get very hot and stuffy. Fresh air is important when it comes to reducing moisture levels, keeping your plants cool and improving air flow.
Some polytunnels have air vents/’windows’ on the sides, which can be opened or shut depending on the weather.
Some polytunnels can be extended. This is a great option for those who don’t currently have the space available for a large polytunnel, but may do later on. You should be able to purchase additional sections which can be attached to your polytunnel if you move to a larger area.
Allotment Polytunnel FAQs
Is a poly tunnel better than a greenhouse?
Polytunnels and greenhouses work in similar ways, both designed to boost your harvest and protect plants from bugs and birds.
There are several advantages to owning a polytunnel. They can be built onto a soil base and they’re very easy to assemble. Polytunnels can be stored easily, moved around the garden and are relatively simple to disassemble.
Greenhouses on the other hand are more expensive. They’re a much more permanent structure. While greenhouses can look great, they aren’t the best option if you lack garden space and the ground they are built on must be hard and level. They will however, last much longer than polytunnels.
How do polytunnels work?
Polytunnels provide protection to plants and can let you continue growing weeks after the season’s end. The material used to build them allows the interior to heat up from the sun. The warm air and humidity is contained, creating a microclimate which allows plants to grow – including those that wouldn’t naturally grow in the UK!
Polytunnels also protect your plants from bugs, birds and animals; they often have mesh windows that allow for ventilation without letting pests in.
How long will my polytunnel last?
Polytunnels are usually made up of a steel frame and polythene covering. While greenhouses should last a lifetime, polytunnels have a shorter lifespan. However, polytunnels vary in quality so exactly how long it will last depends on which model you buy.
Generally, a high-quality polytunnel frame could last for up to 20 years, while the polythene cover may need replacing every 3-5 years. Lower quality polythene covers may need replacing annually.