Greenhouse vs. Polytunnel – Which One Is Better?

Hesitating between a polytunnel and a greenhouse? Both types of structures are used for growing a wide variety of crops and flowers. People usually wonder which one to choose as both constructions serve the same purpose.

To make the right choice, buyers should know the difference between a greenhouse and a polytunnel. Various factors, such as ventilation, heat retention, design and so much more should be considered as well. They play a major role when deciding which structure suits your requirements better.

What’s the main difference between a greenhouse and a polytunnel?

Imagine the greenhouse as an attractive glass estate, meticulously designed with solid aluminium or metal frames and clear walls that provide plants with not only shelter but also a picturesque view of their surroundings. It’s like walking into a floral conservatory, where temperature control reigns supreme and beauty meet functionality.

In comparison, the polytunnel is more like an industrious cocoon—flexible, cost-effective, and resistant to extreme weather conditions. Its arching plastic covering may lack the visual appeal of glass but do not underestimate its ability to promote vigorous growth through excellent heat retention, light transmission and space optimisation.

Advantages and disadvantages of both structures

Finding out what are the pros and cons of both greenhouses and polytunnels can certainly help you make an informed decision as to which one fits your needs better.

Polytunnels

Advantages

Disadvantages

Greenhouses

Pros

Cons

Important polytunnel and greenhouse features to take into consideration

Site preparation and construction

Polytunnels can be constructed on a slightly uneven surface in a day. Greenhouses take longer to install. They should be also erected on a perfectly flat and levelled surface. There are several ways to prepare the ground for your greenhouse:

People consider paving slabs to be the best base for a greenhouse. It helps prevent damp build-up and fungal problems, as well as diseases that uncovered soil can develop. Both types of structures should face North-South to avoid direct sunlight.

Ventilation

Most of the plants may dry out if a change in temperature occurs. Polytunnels offer a much better control over its air circulation. Large doors at both ends provide sufficient airflow through the tunnel.

Greenhouses provide ventilation through an opening on the roof, the door and side vents. Keep all doors and vents open during sunny days to achieve effective ventilation.

Durability

When it comes to longevity, there isn’t much of a difference between greenhouses and polytunnels. Both types can last for many years. Polytunnels can serve you well between 15-20 years but the covers need to be replaced every few years.

Wondering how long does a polytunnel cover last? Well, this will depend on where you’ve positioned the garden structure. Place your polytunnel on a spot, protected from strong winds. Clean the covers regularly from fallen leaves and trim nearby foliage. This will keep your polytunnels in good condition for longer.

Most greenhouses may even last for a lifetime if they are well taken care of. We have several tips on how to maintain a greenhouse:

Design

Greenhouses can be the highlight of any garden, especially if they have a fancy design. They come in various shapes and models you can choose from. Orangeries, Dwarf Wall or Victorian Style greenhouses are the most popular designs on the market.

However, polytunnels are a far more practical option, yet not so appealing. They also come in various shapes, forms and sizes – each of them – with their own benefits.

For instance, semi-circular arc-shaped polytunnels allow the rain to run easily off the surface. High-tent polytunnels, on the other hand, allow taller plants, such as tomatoes, to grow as high as they need, so they are great for polytunnel gardening, as well.

Heat retention and shading

These constructions protect crops from bad weather conditions. They create a pleasant environment by retaining heat and moisture. The plastic sheeting that covers polytunnels affects heat retention, too. Note that green polytunnel covers do not let enough light permeate through the tunnel. This makes transparent covers a much better option.

Condensation issues in polytunnels can be resolved by installing Thermal Anti-Fog covers, which effectively reduce moisture levels. This type of sheeting can also improve heat retention.

Greenhouses offer maximum heat retention and better light transmission. They are vulnerable to overheating, though, which is why plants need more shading. There are several ways to achieve this.

Some people paint some of the glass panels to reduce the quantity of light coming through the structure. Fitting your greenhouse partially with external blinds will also have a similar cooling effect. The fixtures effectively prevent the sun’s rays from passing through the glass.

Internal blinds, on the other hand, stimulate heat generation as the sun passes through the glass.

Internal microclimate

Specialised equipment controls the temperature, humidity, airflow and irrigation systems. Polytunnels are prone to drought and so are greenhouses. You might need to add an extra layer of bubble insulation to protect your plants better in cold weather.

The benefits of rainwater collection

Water collection is yet another important factor to consider as rainwater harvesting has many benefits. It is an eco-friendly process, a money saver and a nutrient supplier. Greenhouses are easier to adapt than polytunnels, with regards to fitting them with an effective rainwater harvest system.

A good solution to the water collection problem in polytunnels is using a gutter system. You can install a rainwater gutter to one of the sides of your polytunnel, leading straight into a water tank. This way, you’ll have a sufficient quantity of irrigation water that you can use whenever you need to.

What can you grow in a polytunnel and a greenhouse?

There is certainly a big variety of plants that you can grow in both structures. Below we provide some ideas…

What to grow in a polytunnel?

Fruits:

• Strawberries – Mix in some compost with the soil before you plant them.
• Raspberries – Add mulch to the soil to keep it moisturised.
• Melons – They like humid conditions and fertilised soil.

Vegetables:

• Tomatoes – Boost the soil by adding organic matter to it before planting.
• Cucumbers – Create vertical structure in order to allow the crops to grow in a polytunne.
• Artichokes – They thrive well thanks to the warmth and humidity that polytunnels create.

Herbs:

• Rosemary – It grows well in warm conditions and does not need frequent watering.
• Oregano – It helps soil moisture retention.
• Basil, Thyme, Chives – They repel various pests and protect the crops around them.

Trees:

• Peach – Polytunnels protect them from frost and birds that like their fruits.
• Apricots – They need some extra heating.
• Citrus (Lemon, Orange, Lime, Grapefruit) – Polytunnels retain the ideal temperature for them to thrive in the winter months.

Flowers:

• Tulips, Sweet Peas, Foxgloves, Lupins – They attract bees, pollinators and other beneficial insects.

What to grow in a greenhouse?

Flowers:

• Roses – They need enough moisture and around 6 hours of direct sunlight per day.
• Tulips – These plants need protection against pests and frost, so this is the perfect environment for them.
• Orchids – Provide them with the right temperature. Avoid over-watering them.
• Lupin – Constant sunlight and moisturised soil is what they need. Lupins can grow in most soils, even those that are poor in nutrients, except in chalky soil.

Vegetables:

• French Beans – A sunny spot and moisture is all they need.
• Aubergines – Warm the soil a couple of weeks before planting to protect them against frost.
• Peppers – Water and fertilise them regularly. Place peppers in a sheltered, sunny spot.

Fruits:

• Grapes – Water them frequently during the growing period.
• Kiwi Fruits – They should be grown in sheltered sunny spots.

Crop options are limitless. Both types of facilities create appropriate conditions for crop growing. Polytunnels are usually used for growing large amounts of fruits and vegetables. On the other hand, greenhouses are better-looking structures. They are often used for growing various classic or exotic flowers or even tropical fruit.

Did you know why are greenhouses called ‘green’?

Greenhouses are eco-friendly structures which reduce energy bills. They are also good for the environment. They improve the air around your house. People often ask “Why are greenhouses called green when they are invariably clear glass or plastic?”.

According to some studies, greenhouses are called this way because they used to be treated with a green dye. It absorbed light and produced heat. In fact, people still use it today in salt production. It increases the absorption of UV light by the sea in order to speed up evaporation.

Greenhouse sheeting is usually made from translucent materials – clear plastic or glass. This allows sunlight to come in and stimulate the photosynthesis process. It combines carbon dioxide and sunlight’s energy which feeds the plants. Around 6 hours of daily sunlight exposure is what plants need thoroughly.

Do I need planning permission for a polytunnel in my garden?

Polytunnels that are used for domestic purposes are known as ‘permitted developments’. Commercial polytunnels are not considered as such.

There are regulations that should be followed. The structure should be within a certain height, position, size, movability, etc. A local planning authority can decide if you need planning permission for a polytunnel or a greenhouse. You can find some additional information on Planning Portal.

Don’t hesitate to contact your local council office to get some more information in details. Or, you can always find your answers online.

Before you make a decision, take your time to plan and define your needs. Both structures come in various shapes and sizes. Greenhouses are appropriate for you if you want something extra appealing for your garden. They create optimal environment for various exotic plants.

On the other hand, polytunnels are something you might not want to place next to your house but in the backyard instead. Being easily expandable makes them appropriate for growing large quantities of edible plants and start up various flowers from seeds. They are more flexible and are the less expensive option, too.

Did you find this article helpful and worth sharing? Or do you have any other interesting ideas on what you can grow in a polytunnel? Let us know in the comments below!