The Differences Between a Greenhouse and a Polytunnel

At a Glance

Greenhouses use rigid glazing and suit permanent, space-efficient growing with containers, shelving and staging. Polytunnels use flexible polythene covers and provide more open growing space for beds and larger crops. The choice between greenhouse vs polytunnel depends on available space, budget, crops, site conditions, maintenance and available irrigation systems.

Harvst’s WaterMate systems can support irrigation, as they can be configured to suit the watering needs of either growing structure. Purchase a pre-configured system that can adapt to different setups or build your own to suit your greenhouse or polytunnel watering needs.

Greenhouse vs Polytunnel – Understanding the Key Differences

Choosing between a greenhouse and a polytunnel usually comes down to what you want to grow, how much space you have and what your garden can accommodate. 

Both structures create a more sheltered environment for vegetables and other plants, but they differ in construction, cost, ventilation, durability and how the growing space is managed.

Understanding what a polytunnel is and how it compares with a traditional greenhouse can help you choose a structure that fits your growing plans. If you are weighing up the greenhouse vs polytunnel question, this comparison can help you decide which option best fits your space, growing goals and gardening routines.

What is a Polytunnel?

A polytunnel is a growing structure made from a series of hoops covered with a flexible polythene sheet. The covering lets sunlight into the growing area while protecting it from wind, rain and colder conditions.

The shape gives you a practical space for growing crops directly in the ground, with enough room for planting rows and paths. A polytunnel can be especially useful for crops such as tomatoes, peppers and cucumbers that benefit from a warmer, sheltered environment.

But what is a polytunnel used for in everyday gardening? Gardeners use polytunnels to raise seedlings and grow crops that may struggle in an exposed garden, but they still need to manage the growing conditions inside. Things like ventilation, watering and temperature can all affect how well plants perform, especially during periods of warm weather.

What Is a Greenhouse?

A traditional greenhouse has a rigid frame with glass or rigid panels forming the walls and roof. Frames are commonly made from aluminium or timber and the structure is designed to remain in place as a permanent growing space. The rigid construction works well for gardeners who want to grow plants in containers, raise seedlings or use shelving and staging. A greenhouse can make good use of a smaller footprint because you can add growing space vertically with shelves and benches.

Because a greenhouse requires a suitable base and sufficient space for access, cleaning, and maintenance, its placement in the garden is also important. The required size depends on the available site.

With that in mind, the difference between a greenhouse and a polytunnel becomes easier to understand, as the choice between them is not only about appearance. The structure, covering and available space can also help you decide how each option would work in your space. 

Structural Differences, Frames, Covering and Lifespan

The most obvious structural difference is the material surrounding the growing areas. A greenhouse uses rigid glazing, usually glass or a rigid plastic panel. The glass provides a permanent covering and allows good light transmission, but individual panels can break and require careful replacement.

A polytunnel, on the other hand, uses flexible polythene stretched over its frame. When properly installed, the covering can withstand normal outdoor conditions, but it is a consumable part of the structure and may eventually need replacing due to weather and UV exposure. 

This difference is one of the main factors to consider when comparing a greenhouse vs polytunnel, as each structure has different maintenance requirements.

The frames also affect installation, as greenhouses require a firm, level base, while polytunnels need secure anchoring to keep the frame and covering stable in windy conditions. The site itself also deserves attention before installing either structure. Check the ground, drainage, exposure to prevailing winds and access to the growing areas, as these factors can affect maintenance throughout the year.

Cost and Installation Comparison 

The initial cost can vary considerably for both structures depending on their size, materials and installation requirements. As a rough guide, a small greenhouse may cost between £200 and £1000, while larger or more advanced models can range from £1000 to £5000 or even more. Similarly, a polytunnel may cost approximately £300 to £2000 depending on the size, frame, cover and installation.

A small greenhouse may work well in a domestic garden where space is limited. Larger models can require a more substantial base and additional equipment such as staging, shelving and automatic vent openers.

Polytunnels can provide a sizable growing area with a relatively straightforward frame and covering systems. However, the total cost should still include ground preparation, anchoring, the polythene cover and any internal equipment you plan to install. 

Installation is only the starting point and once either structure is being used for vegetables, you also need to think about how water will reach the plants and how excess heat will be managed.

Watering and Ventilation Needs for Each

Watering becomes important in covered growing space because natural rainfall cannot reach plants inside. The amount of water needed depends on the crop, growing medium, temperature and stage of growth, so a fixed routine does not always suit every plant. 

Ventilation is also equally important, as warm air can build up inside a greenhouse or polytunnel quickly during sunny weather. That is why doors, vents and roll-up sides need to be used appropriately to let heat escape. This can also make summer care demanding, as plants may need more water just when gardeners have less time to check on them.

Here, a smart automated irrigation system like the Harvst WaterMate can help maintain a more consistent watering routine. Harvst WaterMate Systems come with timers and sensors to adjust watering based on conditions, giving gardens a way to manage irrigation without relying entirely on manual watering. 

For smaller growing spaces, the WaterMate Mini is designed for greenhouses or polytunnels of up to 6 by 8 feet, or approximately 6 square metres. It supports two watering zones and can run from a 10W solar panel or 240V mains power, with water supplied from a water butt or garden hose. For larger growing areas, the WaterMate Pro supports additional watering zones. This lets different areas of the growing space follow different watering schedules, which is helpful when crops have varied needs. 

Harvst’s Build Your Own automatic irrigation system also lets gardeners configure pumps, valves, pipework and other tools around their gardening area and water source. 

Which Growing Structure Suits Your Space?

The best choice depends on your growing goals and the conditions around it. A greenhouse can suit a smaller garden where permanent structure, container growing and shelving are useful. It can also work well when you want a defined growing area close to the house and have a suitable base available.

A polytunnel is the right choice when growing capacity matters more than a compact footprint. Its open interior works well for vegetable beds, planting rows and larger crops, making it particularly useful for allotments and larger gardens.

Your water supply should also factor into the decision because if your greenhouse or polytunnel is close to the house or mains water, a water butt or tank combined with a suitable pump can make irrigation easier to manage. When time is limited, an automated irrigation system can also help maintain consistent watering without daily manual watering.

Ultimately, understanding the difference between a greenhouse and a polytunnel can help you choose the best option depending on your space, crops, local conditions, water supply and available maintenance time.

Plan Irrigation for Your Growing Space with Harvst

Once you have chosen between a greenhouse and a polytunnel, the next step is working out how you will manage water throughout the growing season. 

Harvst’s WaterMate range is designed for different growing spaces and can be powered by solar or mains power. Water can be supplied from a hose, water butt or tank, giving you flexibility when planning your irrigation setup.

Want to see it in action? Harvst’s Making Gardening Easier | Off Grid Watering System | Allotment Gardening UK video shows how a WaterMate Pro can water a polytunnel alongside other outdoor growing areas. It gives a useful example of how one irrigation system can be configured around different parts of a growing space.

If you are considering an automated setup, buy the WaterMate range to simplify watering or build your own if you have specific watering requirements for your growing space.

Product specifications and features are subject to ongoing improvement. For the latest details, please see individual product listings.