High Tunnel Greenhouse – a strong, spacious growing structure for vegetables, seedlings and a longer season

Our Bloomcabin High Tunnel Greenhouse is designed for growers in the UK who want generous protected growing space without relying on a lightweight seasonal polytunnel. The fixed polycarbonate covering, reinforced zinc-coated steel frame and close arch spacing create a practical structure for intensive home or small-scale growing.

The tunnel is 3 m wide and 2.10 m high. The base length is 4 m and can be extended in 2 m sections. The Omega-shaped steel profiles are 56 mm wide and 1 mm thick, arches are spaced 1 m apart and each arch is anchored approximately 35 cm into the ground. The structure is rated for a snow load of up to 160 kg/m². Explore our Greenhouses & Conservatories and Useful Information.

More substantial than a basic polytunnel and more growing volume than many compact garden greenhouses

For UK gardens and allotments, it is also worth noting that This model focuses on practical growing capacity, structural strength and the ability to extend the tunnel as your planting plans develop.

Key specifications of the Bloomcabin High Tunnel Greenhouse

Width: 3.00 m.

Height: 2.10 m.

Length: base model 4 m, extendable in 2 m sections.

Frame: zinc-coated steel, 1 mm thick.

Profile: Omega-shaped profile, 56 mm wide.

Arch spacing: 1 m.

Snow-load capacity: up to 160 kg/m².

Ground anchoring: each arch extends approximately 35 cm into the ground.

Covering: 6 mm polycarbonate with UV protection.

Access: 1 front door.

Ventilation: 2 side windows for airflow and temperature control.

Warranty: 10 years according to the applicable product terms.

A front door and two side windows help you manage both daily access and the growing climate

For UK gardens and allotments, it is also worth noting that The tunnel height provides comfortable headroom for working and gives tall crops such as tomatoes and cucumbers the vertical space they need.

For UK gardens and allotments, it is also worth noting that Two side windows provide additional airflow. Ventilation becomes especially important on bright days because a protected growing structure can heat up quickly.

For UK gardens and allotments, it is also worth noting that Opening the side vents at the right time helps manage heat and humidity while maintaining better air movement around dense plant growth.

A high tunnel can support much more than one crop or one season

For UK gardens and allotments, it is also worth noting that The generous width, extendable length and useful working height allow the interior to be organised around several different growing strategies.

Choose the site, prepare the ground and think about ventilation before the frame goes up

Choose a reasonably level position with good sunlight and enough clearance from trees, walls and other obstructions.

Because each arch is anchored approximately 35 cm into the ground, make sure the ground is suitable and check for buried services or other obstacles before installation.

Plan paths, irrigation and convenient access to the front door before deciding the final tunnel length.

For more planning and ordering guidance, see our Useful Information.

When does a high tunnel make more sense than a classic aluminium greenhouse?

For UK gardens and allotments, it is also worth noting that A classic aluminium greenhouse places more emphasis on architectural appearance, colour choices, glazing options and integration with the landscaped garden.

For UK gardens and allotments, it is also worth noting that The High Tunnel focuses on productive protected growing space, robust functionality and straightforward modular expansion. Its width stays constant while the tunnel grows by adding length.

For UK gardens and allotments, it is also worth noting that Choose the High Tunnel when crop production and protected growing volume are the priority. Choose a classic greenhouse when visual customisation and a more architectural garden feature matter more.

Use the tunnel to manage rain, wind and a relatively short warm season

For many UK gardens, the value of a rigid high tunnel is not simply extra heat. Keeping persistent rain off crops such as tomatoes while creating a more stable space for spring and autumn growing can be just as important.

Conditions vary between southern England, exposed coastal areas, inland sites, Wales, Scotland and Northern Ireland, so planting dates should follow the local garden rather than a national timetable. A sheltered southern plot may warm much earlier than a windy northern allotment.

The tunnel is most effective when those differences are recognised. Use it for the crops that genuinely benefit from protection and leave robust outdoor vegetables in open beds where space under cover would be wasted.

A wet garden needs a dry, stable installation area before the frame goes up

UK rainfall makes drainage especially important. The ground around the tunnel should not become a basin where roof runoff or surrounding surface water collects around the anchored arches.

If the plot is heavy clay or prone to winter waterlogging, improve the surrounding drainage before installation rather than hoping the tunnel will solve the problem. Raised beds can help crop roots, but the frame itself still needs stable ground.

Because each arch extends around 35 cm into the soil, check for buried cables, water pipes, drainage runs and other services before work begins. A well-drained site is safer for both plants and structure.

Coastal and open allotment sites need careful orientation and routine checks

Wind can be a bigger challenge than snow in many parts of the UK. Exposed coastal gardens, open fields and allotments may experience repeated gusts that put doors, vents and panel fixings under regular stress.

Choose a position that avoids obvious wind tunnels between buildings or solid fences. Some distant shelter can help, but the structure still needs free airflow and good sunlight around it.

After strong storms, inspect door alignment, vent hardware, polycarbonate fixings and ground anchors. Catching a loose component early is much easier than repairing secondary damage after several days of wind.

Protect foliage from rain but do not replace rain with trapped humidity

Tomatoes are one of the obvious UK crops for protected growing because the roof keeps repeated rainfall off leaves and fruit. That advantage is reduced if the tunnel remains closed and humid air cannot escape.

Open the side windows whenever conditions permit, particularly after watering and during warm spells. Good spacing and removal of excessive lower foliage can also improve air movement within dense tomato rows.

Gurkins, cucumbers, peppers and chillies can share the protected space, but taller crops should be arranged so they do not shade every lower plant as summer progresses.

Make the protected area productive before and after the main summer crop

A high tunnel can support salads, herbs, radishes, young brassicas and propagation trays before tender summer crops take over. This is particularly useful when outdoor soil is wet or cold but daylight is improving.

At the end of summer, fast-growing greens can return to cleared sections. The tunnel does not create winter daylight, so expectations should remain realistic as days shorten, but protection can still extend useful harvest windows.

Planning crop succession before the season starts prevents the tunnel from sitting half empty in spring and autumn while all attention is focused on tomatoes.

Rainy weather outside can still mean dry soil inside

It is easy to underestimate irrigation in a wet British summer because outdoor beds may be saturated while the tunnel soil remains comparatively dry. The roof deliberately prevents rainfall from reaching the crop rows.

Drip irrigation or a seep hose can supply roots without repeatedly wetting foliage. Watering in the morning gives excess moisture more time to dissipate through the side windows during the day.

Rainwater collection can be useful, but tanks should not block access or create permanent shade. Longer tunnel versions benefit from separate watering zones so different crops are not forced onto one schedule.

Check the site rules before assuming a permanent tunnel can go anywhere

High tunnels can suit productive allotment plots very well, but individual sites may have their own rules on structures, dimensions, anchoring or appearance. Those requirements should be checked before purchase.

On a private garden, local planning or boundary considerations may also be relevant depending on the exact project. It is better to clarify them before setting out the 4 m base than after the frame is installed.

Where space is limited, keep a practical path around at least the key access and maintenance areas. Squeezing the tunnel against a fence may save centimetres but make cleaning and repairs unnecessarily difficult.

Use quieter months to inspect the shell, clean panels and prepare beds

After the main season, remove dead crop material, old strings and damaged supports. This reduces hiding places for pests and makes it easier to inspect the steel frame and polycarbonate properly.

Clean panels with methods suitable for polycarbonate so winter grime and algae do not reduce light more than necessary. Check M5 fasteners, D40 tabs, door hardware and side windows at the same time.

If snow does fall, the stated 160 kg/m² capacity is useful, but wet or drifted snow should still be monitored. Winter storms in the UK may combine wind and precipitation, so the whole structure deserves a post-storm check.

Four metres is manageable for many gardens; extra modules should earn their space

The 4 m base model offers enough protected area for several productive rows without dominating a typical garden. Additional 2 m sections make sense when you know how the extra space will be used.

Before extending, consider whether irrigation, access and crop rotation remain practical. A longer tunnel with a narrow blocked path can be harder to manage than a shorter, well-organised structure.

If later expansion is possible, keep the extension end free from permanent sheds, trees, compost bays or paving layouts that would make the next module awkward to add.

FAQ – Bloomcabin High Tunnel Greenhouse