Setting Up a Tunnel House

August 15, 2014 Niki Morrell

Like everything we tackle on our lifestyle block, setting up the tunnel house has been a process of trial and error.

It’s dragged on a bit, with bursts of frenzied activity alternating with long lulls as other projects have taken priority.

It’s still not finished but I’m hoping we’ll get it completed by mid-spring.

Step 1: Covering the frame

When we arrived here, the frame was standing but it wasn’t covered. We had the plastic, so we waited a month until our first batch of house-guests arrived and then we roped them in to help.

There are two ways of covering a tunnel house. The first is to dig a trench around the frame, pull the plastic tight over the ribs and bury the edges in the trench.

The second is to pull the plastic tight over the ribs, wrap the edges around wooden battens and then screw the battens onto the frame. This is the method we used.

Before the plastic went on, we covered the outside edges of the frame with anti-hot spot tape. This insulates the metal ribs against summer heat so they don’t melt the plastic. It also cushions against rubbing.

Covering the tunnel house

Covering the tunnel house

Step 2: Drawing up a plan

It’s important to be clear about the purpose of your tunnel house because this will influence how it should be set up, particularly with irrigation.

Some people use tunnel houses purely for propagating plants in containers. Others need long growing beds for vegetables. I wanted to use ours for both.

Our tunnel house is 11 metres long by 9 metres wide. We basically divided the area into thirds lengthwise, with raised growing beds down each side and four large propagating tables in the central area.

We allowed for six paths: three running lengthwise and three running across. All needed to be wide enough to admit a wheelbarrow.

Step 3: Building the infrastructure

Ewan began by making the propagating tables so that I could raise seedlings for the vege garden. Then he tackled the sticky problem of the beds.

We had to go with raised beds because the site slopes down to the south and east and the existing clay/shale soil is too stony and rubbishy to grow directly into.

The slope is more gradual on the western side, so Ewan built those beds first, using untreated eucalyptus timber (8”x 2”).

We lined the bases with soaked, perforated cardboard and then half-filled them with compost. A drip irrigation system went in next and we topped up the beds with more compost. Voila! Two-thirds of a functioning tunnel house!

Step 4: Irrigation

Getting the irrigation right has been our biggest learning curve. Along with the drip irrigation mentioned above, we also installed overhead misters.

Three summers of tunnel house irrigation have shown us that our 2l/hr drippers aren’t big enough. We really need twice that size but we’ll wait until we’re installing the irrigation lines in the yet-to-be-built eastern beds, as we’ll have to tweak the water pressure into the system.

Raised beds and irrigation drip lines

Raised beds and irrigation drip lines

Step 5: Review

There’s no question that our tunnel house is a great asset. Without it, I couldn’t grow any veges over winter or guarantee home-grown tomatoes over summer. It makes propagating seedlings and cuttings possible on a much larger scale than otherwise.

The cover has held up very well over three years of freezing winters and hot summers. The sloping site has been a challenge but we’ve made do.

Now, all that’s left is to finish it!

Tunnel House Result!


About the Author

Niki Morrell is a writer who is learning how to farm 25 hectares of marginal land and beech forest in the Nelson Lakes area. With no background or prior experience in farming, she spends much of her time alternating between elation and despair. She says, however, that she wouldn’t have it any other way.

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