Robust polycarbonate high-tunnel greenhouse with generous protected growing space for vegetables, seedlings and an extended garden season

The Bloomcabin polycarbonate high-tunnel greenhouse is designed for gardeners who need a generous, permanently protected growing area for vegetables, seedlings and warmth-loving crops. The three-metre-wide tunnel shape provides practical floor space for clearly arranged beds, a working path and irrigation. Unlike a flexible film cover, six-millimetre polycarbonate panels form a fixed cover over the galvanised steel structure.

The base length is 4 m and can be adapted to the required growing space with matching extension sections. The galvanised steel frame is anchored into the ground through its arches. Together with the permanently fitted polycarbonate cover it creates a stable, sheltered growing space. Explore our greenhouses and conservatories as well as our guides and planning advice.

More protection than a simple film tunnel – and considerably more growing space than many compact garden greenhouses

This model suits anyone intending to use the area regularly for vegetable and plant growing. It provides room for permanent beds and working paths, while the selectable length can still be matched to the property and actual space required.

Key details of the Bloomcabin high-tunnel greenhouse

Width: 3.00 m.

Height: 2.10 m.

Length: Base model 4 m; extensions in 2 m increments.

Frame: Galvanised steel, 1 mm material thickness.

Profile: Omega profile, 56 mm wide.

Arch spacing: 1 m between arches.

Snow load: 210 kg/m².

Ground anchoring: Each arch extends approx. 35 cm into the ground.

Cover: 6 mm polycarbonate with UV protection.

Access: One door at the front.

Ventilation: Two side windows for managing temperature and air exchange.

Warranty: 12 years under the applicable warranty terms.

A front door and two side windows make access and internal-climate control easier

The internal height makes upright work easier and provides space for tall crops such as tomatoes or cucumbers. The front door is the main entrance. Keep the area immediately behind it clear so watering cans, harvest containers and garden tools can be carried in and out without damaging plants.

Both side windows must remain freely accessible from inside and outside. Position plants, supports and stored items so the windows can be operated fully. When planning beds, also check that the windows remain reachable once crops are fully grown.

Open and close the door and windows regularly to check their smooth operation. Remove soil and plant debris from moving areas. If a component sticks, investigate the cause first rather than forcing it.

Arrange crops for short routes and easy access

When arranging the interior, consider not only plant type but also growth height, monitoring needs and harvest frequency. This makes sensible use of the available space and preserves access to every crop.

Plan the site, ground conditions and future use before installation

Measure the footprint for the chosen tunnel length and prepare an area that is as level as possible. Leave enough working room around the structure during assembly to position arches and polycarbonate panels safely. Also plan surface-water drainage: rainfall from the rigid cover must not collect beside the structure or in front of the door.

As the arches extend around 35 cm into the ground, identify underground electricity, water and drainage services before work begins. Do not wait until assembly to remove larger stones or other obstructions. On uneven land, prepare the area so every arch stands on the same line and the specified installation depths can be achieved.

Plan how components will travel from the delivery point to the prepared site. Keep access clear during assembly; soil, compost and garden tools must not obstruct the work area. Both long sides must also remain accessible from outside for later inspections and maintenance.

Further planning and ordering advice is available in our guides and planning advice.

When is a high tunnel the better choice than a classic aluminium greenhouse?

A classic aluminium greenhouse offers a clean-lined appearance, varied design options and can become a visible design feature in the garden.

A high tunnel instead focuses on a large continuous growing area, robust construction and the option of modular extension.

Choose the high tunnel when you need the greatest possible protected area for productive growing. A classic greenhouse is better when a linear form and visual integration into the garden matter more.

Adapt use and care to your site and local weather conditions

Gardening conditions vary greatly by region and property. Coastal locations often bring wind, damp air and changeable weather, while sheltered inland sites can experience very warm summer days and colder winter conditions. Use the high tunnel according to your garden’s microclimate rather than a fixed calendar.

For early crops, the protected space can provide a clear advantage in spring. Later in the year, warmth-loving plants benefit because rain and wind reach leaves and fruit less directly. In autumn, many crops can be harvested for longer while light and temperature remain sufficient.

During the first season, record notable temperature patterns, particularly damp periods and areas where plants grow less strongly. These notes help adapt planting and care routines more precisely to the site in the following year.

Choose a sunny position and leave enough room for air exchange

A sunny location is especially beneficial in spring and autumn. Observe when buildings, hedges and trees cast shade over the intended area. Keep sufficient distance from obstructions so both side windows can ventilate effectively.

At exposed sites, observe the prevailing wind direction and avoid unnecessary wind tunnels between buildings. Natural wind protection at an appropriate distance can help, but must not permanently shade the tunnel or obstruct air circulation.

Also consider later maintenance when choosing the site. The front door must be easy to reach, and enough room should remain along both sides to inspect windows, polycarbonate panels and fastenings from outside.

Arrange tomatoes, cucumbers, capsicums and early salad crops across a 3 m width

The fixed 3 m width works well for two side beds with a central working path, or three narrower growing zones. Position tall plants such as tomatoes and cucumbers so they do not unnecessarily shade lower crops. If using strings or plant supports, plan their fixing points before planting.

In spring, salad crops, kohlrabi, radishes, herbs and seedlings can use the protected space before warmth-loving summer crops take over. After the main season, part of the tunnel can be used again for hardy leafy vegetables or late herbs.

Mark occupied bed sections and record which crops grew there. This makes planning the next planting easier without having to reorganise paths or ventilation areas.

Act early on hot days before heat and humidity build up

The interior of a closed tunnel can heat up quickly on sunny New Zealand days. Open the side windows before plants show signs of heat stress where possible. Early ventilation moderates temperature peaks and removes humid air from dense planting.

For tomatoes in particular, it is useful to keep leaves as dry as possible and avoid unnecessarily encouraging condensation. Ventilate on mild days too when outdoor air allows good exchange. After watering, excess moisture should be able to escape from the crop.

During prolonged hot periods, changing watering times and adding temporary shade where needed can help. The best approach depends on the region, orientation and crops.

Deliver water to the roots rather than dampening the entire interior

The polycarbonate cover keeps most natural rainfall off the beds. Watering must therefore be managed deliberately. Drip lines or targeted watering are particularly practical because they take water directly to the root zone and keep foliage drier.

Watering frequency depends greatly on soil type, temperature, crop size and density, and the season. Heavy soil holds water differently from sandy ground or a raised bed. Do not water to a fixed weekly schedule; check actual soil moisture instead.

Collected rainwater can be used to water the beds. Position containers and route lines so paths and access to the front door remain clear.

Start with 4 m and match extensions to actual space requirements

The base length already provides room for several crops in many home gardens. Additional sections make sense where more cultivable bed area is permanently required. The high tunnel can therefore grow with vegetable production or gradual development of the property.

Before the first assembly, still consider the possible final length. Paths, irrigation lines, compost areas and adjoining beds are easier to plan when a future extension direction remains clear.

A longer version may suit smaller food-producing gardens where several crop groups need separating. Choose the extra space only if it can genuinely be maintained, watered and planted.

Check the frame and fastenings before winter and after severe weather

Snow can vary greatly in weight according to moisture, wind drift and temperature, and may collect unevenly on the roof.

Inspect the tunnel externally after severe weather, strong winds or heavy snow where relevant. Unusual deformation, loosened fastenings or uneven snow accumulation should be checked and addressed promptly. Remove snow only in a way that does not damage polycarbonate panels or the steel frame. Do not use sharp tools or walk on the cover. Avoid creating a heavily one-sided load while clearing.

Before the colder season, systematically inspect M5 screws, D40 plastic washers, side windows, the door and ground anchoring. Clean the transitions between frame and panels, remove plant debris and ensure every moving part closes. Do not leave loose pots, tools or supports inside where they could strike the panels. Work from the entrance to the tunnel end so less visible areas are included.

Replant beds in order and use the cleared tunnel for inspection

Plan the sequence of intended crops early. A bed can then be prepared specifically for its next planting after harvest, without affecting neighbouring crops or the working path.

Clear harvested sections completely before planting the next crop. Remove diseased plant material from the tunnel and prepare the soil for the intended follow-on crop. At the same time, inspect plant supports and irrigation components in the relevant bed.

After the final clear-out, remove ties, empty pots and labels, and clean work surfaces. Check irrigation for blockages or damage. Then use the open interior for a thorough visual inspection of the frame, fastenings and panels, which are easier to access without dense foliage.

Generous protected growing space for allotments and home gardens

The high tunnel suits larger home gardens as well as sites where efficient use of the available growing area matters more than the decorative appearance of a classic greenhouse. Its functional shape puts protected plant space first.

Before installation in an allotment or shared garden, check the applicable rules. Confirm whether requirements apply to size, location or setbacks before ordering a longer tunnel version. Also ask the relevant council whether building or resource-consent requirements apply to the particular site and use.

The consistent width makes paths, beds and irrigation easy to arrange clearly and repeatably, including after a later extension.

FAQ – Bloomcabin high-tunnel greenhouse