Collection: Tunnel greenhouse

What a Polytunnel Is

A tunnel greenhouse, also called a polytunnel or hoop house, is built from a series of curved steel hoops covered with a polythene skin. The arched profile gives a large enclosed volume from very few structural parts, which is why it covers more ground per pound than any glazed structure.

It is the format used by commercial growers and allotment holders for the same reason: maximum covered area for the cost, with an assembly that needs no glazing and no specialist tools.

Where It Wins

• Cost per square metre is lower than any glazed alternative.
• Assembly is faster, with fewer parts and no panes to fit.
• The curved profile sheds wind rather than presenting a flat face to it.
• Length can be extended by adding hoops rather than replacing the structure.

For growing vegetables in volume, this is usually the sensible answer. For a structure that will be looked at from the house, a glazed frame from the main range suits better.

The Cover Is a Consumable

The polythene is the part that wears out. UV degrades it over several seasons until it clouds and eventually tears, usually starting at a stress point near a hoop or a door frame.

Replacement covers are sold separately and can be fitted without touching the frame, so the structure long outlives its first skin. Check availability for the model before buying, since a tunnel with no replacement cover is a temporary purchase.

Ventilation Through the Length

A tunnel holds a lot of air and heats considerably through the middle of the day. Doors at both ends are the primary means of cooling, and opening both sets up a through draught along the whole length.

Side vents or roll up sides help in longer tunnels where the centre stays still. A circulation fan is worth considering in dense planting, and shade netting over the top takes the peak off in midsummer.

Anchoring and Ground

A tunnel is light for its size and presents a very large surface, so ground anchoring does almost all the work of keeping it in place. This is the most common point of failure and the least forgiving.

Our anchor kits cover soil and gravel, which are the usual bases. Fit them properly at the outset and check them each spring.