Introduction to Polytunnels
1.1 What is a polytunnel?
A polytunnel usually consists of a metallic, plastic, or wooden frame, covered with polythene or other similar materials. Polytunnels usually have an elongated shape, strongly resembling a tunnel.
Different shapes and sizes of polytunnels can be built, to create microclimates suited for different types of vegetation.
With polytunnels, it’s easier to grow fruits and vegetables that wouldn’t normally thrive in your climate. Additionally, they offer protection for your crops, against harsh weather conditions, such as; hail, high winds, frost, and thunderstorms, including animals and certain pests.
Advantages of a Polytunnel
As mentioned before, a polytunnel will allow you to grow fruits and vegetables, that otherwise would not thrive in your climate. In warmer climates, polytunnels can extend the season of growth for many months, (sometimes all year round).
Humidity, irrigation, and airflow can be easily controlled and adjusted. Polytunnels are much more affordable than greenhouses and are also easier to install and maintain.
Crops in the polytunnel will thrive in any season, providing the perfect germination environment in the early spring, due to higher sunlight absorption. Your tunnel will be hot in the summer and keep your plants alive in the winter if insulated properly.
The possibility of installing, a simple yet effective irrigation system, makes growing crops in your tunnel even easier.
It is possible to create a “Mediterranean” climate in the tunnel, meaning you can grow more exotic fruits and vegetables. If you use bubble wrap to insulate it in the winter, you can prolong the growing season even more. After the winter is over, you can remove the bubble wrap and reuse it next year.
Polytunnels are much more affordable than greenhouses, and instead of buying a small greenhouse, you can build a polytunnel 4-5 times of its size, for the same cost. Polytunnels can be more easily moved around the garden, making it easier to rotate crops when necessary.
Polytunnels are used to grow most of the fruits and vegetables we can buy in the stores. Increasingly large numbers of farmers use polytunnels, as a green alternative to increase their crop production. Farmers, that are otherwise limited to grow specific crops, due to their climate (in the UK for example), are now able to grow chili, tea, coffee, kiwis, and grapes.
Essential Gardening Equipment
Soil pH Testing
You need to make sure that you accurately test your soil to give your plants the best chance.
We use and recommend this 4 in 1 hygrometer to measure soil moisture, pH levels, nutrients, and light conditions at the same time.
The best way to germinate your seeds so that they have a great start is with a germination kit. Seeds that are grown this way produce greater results.
A trusted spade is a gardener’s best friend, it helps you do the work. A long-handled spade is the most effective type.
Gardening Tool Set
For the finer work in the garden, we need those handy tools to help us cultivate. One that you can carry around in the garden is best.
Every advanced gardener has a greenhouse and with so many benefits how can we do without. The acceleration and growth rate when using a greenhouse is worth the cost. Dehydrating
One of the issues people have is that their crops produce all at once. The best way to overcome this is with a dehydrator so you can store your food for years and the flavor is amazing.
Disadvantages of a Polytunnel + Solutions
- The polythene can be damaged by birds and other animals
- If not properly installed, it can be moved by strong wind
- They don’t allow the rain to enter, (so you have to set up an irrigation system or water regularly)
- It has to be ventilated properly, to avoid excess humidity (and mold)
- It can overheat in the summer
If you build your polytunnel with care and ventilate it properly, you should already be avoiding two of the disadvantages.
When it comes to rain, most of the time we have to water our gardens regularly, despite some rainfall in the season. When watering and irrigating your polytunnel, should be much easier and more controllable, as it will retain humidity for longer. If the tunnel overheats in the summer, you can cool it off with water, proper ventilation, added shading or even fans.
Will My Crops be Bigger + Grow Faster?
With proper care, your crops will grow faster, bigger, and for extended periods of time (earlier and longer than in your garden).
The plants that are proven to be healthier and grow faster, include; onions, beetroots, sweetcorn, tomatoes, and strawberries. You can even grow onion from seeds, and it will be much healthier, and suffer from fewer pests, compared to planting it outside.
Quicker and fast mature
For example, you can enjoy vegetables (like French beans) much earlier, and eat your first plate of beans before the outdoor beans even start to bloom!
Due to the prolonged periods, in which you can repeatedly grow some crops, your yield will definitely be bigger than growing solely in your garden.
Temperature differences in the polytunnel
Polytunnels get warmer than the outside temperatures, and the difference in temperature can be substantial. Many of the crops will love this hotter climate. However, proper ventilation is always important when dealing with excess humidity and heat.
The temperatures in your polytunnel will definitely be higher than the outside temperatures, offering you to grow varieties of fruits and vegetables, that you wouldn’t be able to grow in your climate.
The best way to control overheating and humidity is to ventilate it regularly. On very hot days, it might be more challenging to cool it down, so for hotter climates, you can install a different type of polythene and frame (we will discuss this later).
Temperature Increase Examples
If the temperature outside is 90 F (32 degrees Celsius), more likely that the temperature in the polytunnel, can reach up to 110 F (43 degrees). If the night temperature is 70 F (21 degrees), more likely it can reach up to 85 F (29 degrees) or more in the tunnel.
If the temperatures inside the polytunnel reach over 90 F (32 degrees), this might stop the fruiting process of certain crops, such as tomatoes. In this case, it’s very important to keep your tunnel well ventilated, cool it off with water, and even provide some shading if necessary, to keep it at optimal temperatures.
To ensure that the temperatures in your polytunnel don’t drop too low in winter, there are quite a few ways to keep the tunnel warm;
- Insulating your tunnel with bubble wrap
- Protecting the crops with garden fleece and mulch
- Heating up your tunnel (optional)
Depending on your climate and the ability to protect and insulate the tunnel for the winter, you might be able to grow even in the wintertime.
If insulated properly, the temperature difference should be enough, to keep your crops alive and growing. In point 3.5 you can read about, what veggies can be planted in the winter.
Different Types of Polytunnels
Come with the standard design, except for the cover. Instead of a single layer of polythene, they usually consist of double layers, which are reinforced with a nylon mesh. This makes them more resistant and better insulated.
They are more expensive than the regular polytunnels, and don’t allow that much light to come through (compared to regular ones).
Are a mix between a polytunnel and a greenhouse. They use a variety of polytunnel frames, and plastic panels are added on top. They are more expensive than regular polytunnels but are better protected and insulated.
Regular polytunnels (as described before)
What to Grow?
Many of the fruits and vegetables on the market today, are grown in some kind of polytunnel or a greenhouse. You can grow pretty much anything in a polytunnel, except for the crops that are not very fond of higher temperatures and humidity.
Common Polytunnel Plants
The most common polytunnel-grown plants are; tomatoes, cucumbers, potatoes, strawberries, peppers, lettuce, radish, melons, cauliflower, chili, peas, beans, cabbage, onion, carrots, basil, coriander, peaches, and grapes. We will give you more information about this, in the following chapters.
Types of Polytunnels
The sizes of tunnels can be very different, depending on many factors;
- The available budget
- The ability to store your produce
- The extent that you would like to grow your own fruits and vegetables
- The time you can invest in taking care of your polytunnel
- The time and money, it will take to maintain and clean the tunnel
The type of crops you are planning to grow (you can even grow grapevine or fruit trees, while some other crops will require much less space).
Polytunnel for Beginners
If you are a beginner, you can try a smaller more affordable tunnel (220 x 200x 200 / 350 x 200 x 200 cm). These tunnels can be purchased online for less than 100 dollars, but more likely won’t last too many years, and can be used to “test the field”.
If you love to garden, and you have some time and money to spend, investing in a bigger polytunnel is a good idea. These tunnels can be high and long and can spread all over your garden if you wish. Keep in mind, all the above-mentioned factors, when planning the size of your tunnel.
We also prepared an informative list, of approximate sizes of different polytunnels (mini, small, medium, large and commercial), for better understanding.
Different polytunnel sizes
(Note – These sizes are informative only, as polytunnels can come in countless dimensions).
Mini polytunnels start with sizes 118 x 24 x 18 inches (300 x 60 x 45 cm) and similar. They cannot be entered but you can open the sides or the ends, to access your crops.
Domestic garden polytunnels
These types of polytunnel can be entered most of the time (you can go inside and work on your crops).
- SMALL – starting with 100 x 78 x 78 inches/ 250 x 200 x 200 cm and 137 x 78 x 78 inches/ 350 x 200 x 200 cm
- MEDIUM – approximate examples – 400 x 200 x 200 /157 x 78 x 78 inches and to 800 x 400 x 200 cm /312 x 157 x 78 inches
- LARGER – Larger polytunnels come in all sizes larger than the medium but smaller than the commercial polytunnels described below. For example – 800 x 400 x 280 cm (26 x 13 x 9 feet) and more.
Commercial polytunnels are designed to grow large amounts of fruits and vegetables and are often used by big farms and companies that sell fruits and vegetables at the market.
Some passionate gardeners or small farmers might decide to invest in one of these, as it might last for many years, producing enough fruits and vegetables to store until the next year.
- Width can be from 16 – 30 feet (487 – 914 cm or more)- Length can be from 30 – 90 feet ( 914- 2700 cm or more)- Height can be around 8- 10 feet (243- 305 cm) For example: 2000 x 500 x 280 cm (2o x 5 x 2.8 meters) which makes (65 x 16 x 9 feet).
The layout of your polytunnel is very important. You will have to enter and exit it daily, cleaning weeds, watering, and opening the “doors” and potential “windows”, to ensure proper air circulation.
Outlaying your gardening areas, inside the tunnel properly, will make the experience easier and more pleasant, also maximizing the space available to grow crops.
Depending on the size of the tunnel and your personal preference, you can layout the tunnel to your needs, but there are some things that you might want to consider;
- You have to fit in between the plants (to move around relatively easily)
- You can make 1-2 paths in between (or more in very large ones), depending on the size and length of the tunnel
- You want to maximize the space to grow your crops, but not to the extent that you won’t be able to enter the tunnel and work inside.
Low Lying Polytunnels
Tunnels that are smaller in size (and there are quite a few), cannot be entered, and you can access them by opening the sides or the ends of the polythene covers (to ventilate, water your plants and clean the weeds). Many gardening tunnels can be very long but only 18 or 20 inches high, reaching to your knees, for example.
Polytunnels come in many shapes in sizes, from mini, small, medium, and large for home use, and also commercial for bigger farms or mass production.
The duration of the polytunnel depends on the quality of the materials used for the frame, and also the quality of the polythene used for covering.
When it comes to polythene, there are also different types and qualities. The different types of polythene and their specific properties will also be discussed shortly.
Most polyethylene coverings should be replaced every 5 years, but better-quality ones, can last up to 10 years or even more. Read more about duration in the sections, types of frames, and types of coverings (2.4 and 2.5).
Types of frames
The frame is the base of a polytunnel, as it gives the tunnel its structure and stability. The materials used for the frame, determine the tunnel’s durability, stability, and insulation. Each of the materials used comes with its pros and cons.
The most important thing about the frame is, that it should be strong enough to protect the structure from, bad weather conditions such as; hail, storms, strong wind, and snow. There are a few materials that are used in the construction of most frames, and these are;
Resistant to corrosion and strong. It can support the tunnel itself, and additional accessories such as fans, pots, containers, and more. Of course, they are different qualities of steel frames too, as some of the cheaper ones can be thinner and more fragile (can bend and damage more easily, and might collapse under snow).
When choosing galvanized steel frames, invest in better quality ones, that will last you for years to come.
Aluminum is commonly used to construct polytunnels and greenhouses. It’s affordable, easier to assemble, and doesn’t corrode. Aluminum frames don’t retain as much heat in the tunnel, as the steel ones. When it comes to stability and durability in harsh weather (strong winds, lots of snow), the aluminum frames can bend and break easier.
Wood can be an alternative material when building a polytunnel or a greenhouse. It’s relatively easy to shape and adjust. When assembled properly, it can last for extended periods, but only when it’s properly protected (varnished, treated, etc.).
If we fail to protect the wooden structure, different molds, algae, and fungi can attack the wood, and potentially attack your crops too.
Building a wood structure can be durable, strong, and long-lasting when properly treated.
Plastic is very affordable and has good insulating properties. Similar to aluminum, it doesn’t bode well in harsh weather conditions. Especially cheaper plastic frames, can break easily and have to be often repaired or replaced.
It’s an option to consider if you require a lighter, more portable polytunnel, and the weather conditions in your climate are relatively stable.
Types of coverings
- Exceptionally clear polythene – this type of polythene, as the name suggests, allows more than 95 % of light to reach the tunnel. This type can be used in areas with lower light levels
- White polythene – this type allows up to 70 % of light to reach the tunnel. It prevents the heat to build up excessively, and it’s appropriate for plants that naturally grow in partial shade
- Green polythene– allows up to 65 % of light to reach the tunnel. It mostly absorbs the spectrum of red light and it’s UV stable. It resembles the conditions of the forest floor, and it’s appropriate for plants that grow on such habitats.
- Green and white – this type of polythene allows 0 % light in the tunnel. It’s highly resistant to UV damage, and it’s usually used for livestock, storage, or to grow certain types of mushrooms.
Cost of a polytunnel
The costs of a polytunnel can be very different, depending on the materials and the size you want. For simpler, lighter polytunnels, prices start at $60 (250x200x200 cm).
Depending on the nature of the polytunnel (lifelong or just shorter-term use), you will have to invest more or less money. If you just want to test it out, you can always go for cheaper versions. If you plan to grow and store more fruits and vegetables and preserve the tunnel for many years to come, you might want to invest more.
Depending on the construction, the size, and the materials used, a polytunnel can cost you from 50 to more than 1000 dollars. It’s safe to say, that you can buy a good enough polytunnel, for as little as 150-400 dollars, again depending on the size and the strength of the construction.
If you are going big, the prices will be higher, especially if you are hiring people to help you build a custom-built polytunnel. There are many different options to choose from, and most of them can be ordered online and delivered to your doorstep.
Build Your Own
You can always build your own polytunnel, with some basic construction skills, or order the frame and cover it yourself. When it comes to cost, price is no excuse not to have a polytunnel, as they come at many affordable prices, or you can even build one yourself.
Installation – How to Build One
Some polytunnels are relatively easy to assemble and require less work. Those are usually lightweight and smaller ones. When building a large polytunnel, more work will be required, including;
- Digging holes, to safely and efficiently secure the frame
- Assembly of the frame (wooden, aluminum, steel), some of them might be more challenging
- Properly stretching the polythene covers, to ensure the optimal function of the tunnel
Pinning to Ground
As we mentioned, smaller polytunnels might be much easier to assemble, just following the instructions that you get with purchasing one. It might take some time and effort, but more likely you will be able to do it yourself. Smaller and lighter polytunnels might come with metallic pins or poles to secure them to the ground (burying them into the soil).
Larger constructions will need stronger support, therefore you will need to dig holes in the ground, to safely secure the structure of your polytunnel. You can say that they require some sort of a “foundation”. In areas with very strong wind, a foundation can safely secure your polytunnel. The foundations can be set in concrete (the structure and the door frames), to ensure that the tunnel will stay in place.
Using a Polytunnel
The polytunnel will allow you to grow crops, that otherwise wouldn’t grow in your climate (might be too cold).
Benefits of using a polytunnel
They can extend the growing season, and if you live in a somewhat warmer area, you can even use them to grow crops in winter. Building a polytunnel is easier and more affordable than building a greenhouse.
When properly built, it will protect your crops from cold, animals, strong wind, hail, and other harsh weather conditions. Many other polytunnel benefits, were discussed in point 1.2 (Benefits of polytunnels).
What Fruit Can I Plant in a Polytunnel?
Whatever you normally grow outside will be suitable for a polytunnel, depending on the size of the growth and your polytunnel type. With the increase in temperatures, we have looked at, you may also be able to grow more exotic fruits – this will vary depending on your location.
Examples of what you might be able to grow or improve; are strawberries, melons, kiwis, figs, peaches, nectarines, and even grapes.
Which Vegetables Can I Plant a Polytunnel?
Similarly to fruits, you can extend your current range of vegetable produce, to one’s suited to hotter climates. And of course, you will increase the size and yield or your current crops.
Some examples of what you can grow; are peppers, chilies, sweet potatoes, cucumbers, aubergines (eggplants), sweet corn, spinach, lettuce, winter lettuce, onion, carrots, tomatoes, parsnip, garlic, cauliflower, and more.
Which herbs I can plant in the polytunnel?
Some examples of herbs you can grow; are rosemary, marjoram, sage, oregano, thyme, coriander and basil, and other herbs that thrive in a warm and humid environment. Not only do herbs taste and smell good, but they can also help to repel pests and improve the growth of other crops in the tunnel.
What can I plant in the winter?
A polytunnel will extend the seasons allowing you to grow later on in the year than before. A polytunnel will not stop the frost but will delay it. Sun is an important factor, so for cloudy conditions, you may not experience much of a difference.
During the night a polytunnel will have little bearing on protecting your crops from frost. A polytunnel will, however, promote the growth of your crops that are planted in the season.
These veggies can be planted in the late fall or winter; carrots, garlic, kale, radish, turnips, and winter lettuce.
Can I use containers in my polytunnel?
Yes, you can use many different containers in your polytunnel. Smaller or bigger pots, old drawers, old washing machine drums, buckets, and even tires. But if there isn’t too much space in your tunnel, you might want to avoid using bigger containers, to save space, as it might make it even harder to move around.
Maintenance of your polytunnel
You can use different watering techniques, depending on the size of your tunnel. If you own a relatively small tunnel, you will be able to water everything with a hose or watering cans.
However, if the tunnel is bigger, bringing enough water for your plants might be more challenging, and take a lot of time. In this case, you can install automatic or semi-automatic irrigation systems on the ground, or over your head.
If the roof of your tunnel can be opened, you can open it in times of heavy rain.
Polythene water pipes are spread on the roof of the tunnel, with sprinkles positioned approximately every meter along the tunnel. These can easily be connected to your garden hose, and you can simply activate them by connecting them to the hose, and opening the flow of water.
Ground irrigation systems
The ground irrigation systems use a similar principle to the overhead ones, the only difference is they are spread over the ground in your tunnel and spray the water directly into the soil
Manual irrigation (by hand)
Hoses and watering cans, for smaller polytunnels
Care and cleaning
Care and cleaning of your polytunnel are important for many reasons;
- It will help to preserve your tunnel and prolong its life
- Preventive any plant disease, mold, and algae growth
- To check and remove pests
- To remove and prevent bad odors
- It will allow more light to enter the tunnel
You can start, by rinsing the walls and roof of the tunnel with a hose. The next step would be, to get a cleaner that kills algae, and use it to clean algae from the walls of the tunnel.
You can use a bucket of dish detergent, a sponge, and warm water, to clean dirt and insects off the walls of your tunnel. There are some specialized pressure bottles you can buy, that can help to remove stubborn dirt from your tunnel.
If you regularly address this task, your polytunnel will be more pleasant to work with, and you can help to prevent the growth of many harmful plant diseases, algae, and mold.
Regular ventilation of your polytunnel is very important for many reasons;
- Keeping optimal temperatures (helps with overheating)
- Getting rid of excess humidity
- Offering fresh air and proper ventilation for your plants
- Keeping your polytunnel fresher, and allowing pollination to take place
Ventilation of the tunnel should be done often, or even every day if you have the time. Most of the tunnels come with zippable or at least movable doors and “windows”, that can be opened every day, to ensure proper ventilation.
The best you can do for your health, the planet, and your tunnel, is to use natural and ecological pesticide solutions. Many plant-based and relatively harmless solutions, can be found in your local garden store, to help repel pests.
One of the best things you can do in your tunnel is to plant herbs and crops that repel pests. Here are some of the best tips to prevent pests in your polytunnel;
- Cleaning debris and removing sick and weak plants
- Properly cleaning tools and containers
- Promote “predatory” insects (those who feed on the pests)
- Plant different varieties of plants and keep the soil quality good
- Plant herbs and plants that repel pests, such as; Marigolds, Petunias, Chrysanthemums, garlic, lemongrass, rosemary, basil, tansy, mint, and Yarrow (some of these plants will also repel ants, that tend to “farm” aphids)
- Use natural pest repellents that you can buy at your local garden store, or make at home
Overview of polytunnels
Is it worth getting one?
We hope that after reading this manual, you have already discovered if polytunnels are appropriate for you. Regarding all the benefits and very affordable options for every pocket, it’s safe to say, that it’s definitely worth having a polytunnel to grow your crops.
If you want to protect your crops, make them grow faster and bigger, and grow them before and after the season, you found your perfect solution.
Our favorite polytunnels
The easy tunnel (Terra Garden)
The easy tunnel, retains humidity and warmth, keeping the soil at the optimal temperature to enable early planting, protecting the crops from harsh weather, insects, and animals. It’s very easy to install, as it opens resembling an accordion, and folds easily.
It’s very easy to fold and put away for later. The frame consists of galvanized steel, and it’s easy to secure. The cover is UV stable polythene and the ends allow easy ventilation.
The size is 118 x 24 x 18 inches (300 x 60 x 45 cm), but it also comes in different sizes and materials, including; fleece, micromesh, net, and polythene, for diverse growing needs.
The “pop up” greenhouse (Quictent)
This “pop up ” greenhouse it’s very easy to install and fold (when stored). It’s made with eco-friendly material, comes with UV protection, and it’s waterproof.
They provide 6 stakes to help strengthen the structure. It has 4 large zippable doors, which makes ventilation and your movement inside the tunnel easier.
Additional 2 zipping windows, to adjust the temperature, airflow, and sunlight. The size is: 98 x 49 x 53 inches (250 x 124 x 134 cm).
Superdome Grow Tunnel (Bio green)
This affordable Superdome will prolong your growing seasons and give you bigger crops. It comes pre-assembled for easy installation. Two zippable side doors, allow easy watering and ventilation.
The cover is made from strong UV stable polythene. It offers protection from harsh weather conditions, pests, and other animals. The loops of the construction are made with stainless steel to avoid any corrosion and give the tunnel sturdiness.
Its size is 118 x 31 x 28 inches (300 x 78 x 71 cm). These options are extremely affordable and very easy to install. To show you, that polytunnels really come in many shapes and sizes, for every pocket!
We hope, that we provided detailed and useful information on choosing, building, maintaining, and using your polytunnel. May it serve you well, and help you grow healthy and productive crops.