Tunnel House project

When I bought my house in Karehana Bay, Plimmerton I was very surprised to discover there was no vegetable garden. While the whole garden & surrounding trees were overgrown due to the house being empty for a year or more, I also knew it was the family home of the person I bought it from and his parents had lived here their whole life. I guess they just weren’t into gardening, but one of the attractions was the amount of garden area that came with the house especially the rear of the section which had a series of terraces… So I slowly started building raised garden planters for them.

My vege garden 2015:

At the back left you can see the raspberry plant that I obtained from my parents. It is an heirloom raspberry, which my parents had all their life on their farm, and when they retired they brought a cutting from it and replanted at their new house in Ashburton. Years later I asked my Dad for a cutting and over the next three years it established itself and has grown into a healthy big plant, producing lots of delicious raspberries… I slowly built an enclosure around it, both to shelter it and to make netting easier to manage, as birds would eat all of my raspberries if I didn’t!

Between the raspberry enclosure and the bush/edge of my section there was always an unused area – it was clay underfoot, and I had thought of building more raised garden beds there, but kept seeing interesting photos of peoples gardens on NZ Vege gardeners group on FB where they had incorporated a glass house… next step was joining the NZ Greenhouse gardeners FB group and that was that, I was hooked! The transition from idea to minor obsession was fairly rapid: a green house glass thingy?
hmmm too expensive, but what about a tunnel house?

(After lots of research I decided on a Redpath tunnel house so all comments are relative to it, and full disclosure: I have no other incentive than sharing my own good experience, but if anyone actually does want to send me an NFR greenhouse, please do!)

I began quietly working hard to prepare the site (not coincidentally, the same location I recorded the DIG sound FX library and again recorded clay squelchy footsteps for LIQUIDS library but my motive for this development is twofold:

1. extend the growing season in Wellington, so I can grow salads etc through winter
2. create a micro climate so I can grow some exotic flowers, plants etc & photograph them!

Being an optimist I measured the maximum length that I could possibly fit in the available space: from [raspberry enclosure to end of garden] = 4.5 metres and ordered based on that spec… Delivery time was 2+ weeks so I started preparing the site, aiming to be ready for when it arrived.

The day finally came for delivery:

But even after doing a lot of preparation on the site, when the tunnel house kit was placed roughly in position I soon realised I had a lot more excavation work to do! Oh great, more clay to dig out!



Once I had the site properly cleared there was a light rain and at first i cursed it as I wanted to start assembling the tunnel house… But I noticed how the clay surface turned to mush… so after some research I decided to dig a drain around the back of the eventual tunnel house, dropping down to fill a water tank on level 2. The drain was left open at the top, so it can be flushed with a normal garden hose. A lot more digging, and carrying gravel up to the site:

Drainage will be re-assessed in winter, and potentially a second drain could be added, parallel to the main NS path, out to the same collection tank.

After assembling the basic frame of the tunnel house I next spoke to a local landscaping supplies company, and they advised a layer of gravel to stop the clay getting mushy… So the next few days were spent lugging gravel up to the site:







overhead drone shot to check alignment!



I did a rough layout, with the two full length planters I ordered at the same time as my tunnel house & deck chair…

After installing (anti) weed cloth

At this point I made the decision to only install one of the raised garden planters. Having done more research some people prefer to grow in containers as it makes it easier to replace or rejuvenate the soil. It also means plants can grow from ground level, and I was also a little concerned that two big raised gardens would consume a lot of the space in the tunnel house… So I changed tack, and removed one of the raised gardens (which has since been repurposed into other raised planters in my outdoors garden)





The next stage I was a little nervous about. Putting together all the hardware was fun, but putting the roof on was an all or nothing mission. I had read the instructions many times, and watched a few youtube videos and while I knew what to do I was not confident I wouldn’t mess it up. But I knew I had to wait for a windless day, as wrangling the large pieces of plastic would be impossible in even a light wind…

A day or two later was perfectly calm so I set to:

OK I had the main roof on without ripping or tearing any parts of it. The Redpath tunnel house uses a clever system of plastic clips which fit tightly into cavities on the aluminium frame, so it then became a process of locking down one end or side and tensioning the plastic, while adding clips. The sliding door uses the same plastic and clips, so it was a good small section to do first, indoors.

Once the roof was on I would need to put bolts through the frame into ground pegs, so the whole thing didn’t fly away. But I found it easier to work on clipping the plastic by raising one side of the whole structure.

Above is before tensioning, below after:

You might notice I have installed the roof vent too, after cutting a hole for it and clipping the edges. A seperate piece of plastic has been fitted to each end of the tunnel house, with a hole for the window and a hole of the sliding door.



Now I could bolt the whole structure down, both into the ground pegs I had already hammered into the ground and also to the planter, which when full of soil I figured would weigh quite a lot too…



How much soil would I need to fill the raised garden? A lot! I had been spending my spare time ordering a collection of compost, potting mix, peat moss, fertiliser, Zoo Doo etc… and lugging it up to the site!

Slowly filling the planter, dampening it down and wearing an air mask to avoid risk of Legionaires disease!


I also made three DIY Olla to help sustain the watering (watch this video to see how they are made & used)





One crucial aspect of a tunnel house and/or green house is that you provide and control the water. Since no rain can get in you have to monitor and water the plants or… everything will die! The same applies to temperature – I put a thermometer in there & on a sunny day with door & window closed it was reaching over 40 degrees Celcius. So the first thing I did was order an auto vent opener. It is basically a mechanism with a wax cylinder which starts expanding once it reaches 15 degrees C. So the vent will fully open as the temperature rises…

I had a month long trip to Japan planned for the start of their winter, which equates to our spring… So I needed to set up an automated watering system and test it for a few weeks to insure it would be reliable, as I didnt want to arrive home to a dry tunnel house full of dead plants.

For my main outdoors garden I have an inexpensive timer, this one $89 via Mitre 10 so I used it for my greenhouse, with the timer installed at the tap, then maybe 40m of hose to the greenhouse, then a Y junction splitting off to feed two sprinklers. I just used normal lawn sprinklers, hanging upside down from the ceiling using cable ties… While people have mentioned it is better to feed the roots directly and keel the humidity lower I figured the upside down sprinklers act more like rain…

I set it to water for 3 minutes at 7am, and again at 7pm… but after a few days I thought that was too much so I changed to 3 minutes at 7am and 3 minutes every third day at 7pm. Two weeks later it had delivered every day perfectly… So I was reasonably confident everything would be ok… I took a photo and off to Japan I went…

And one month later:


It looks like two totally different photos, but its the same photo taken from the same position – standing just outside the door. I literally could not get into my greenhouse, it was like a jungle in there!!

The biggest tomato plant at the back left had grown like crazy, and taken over about a quarter of the greenhouse!! And all the other tomato plants that I had growing in buckets on the right hand side had grown across the tiles/path…

I spent a few hours in there tidying everything up, removing laterals and some branches from the big tomato plant, and training the bucket tomatos up strings… So this is how it currently looks:

The big tomato has a lot of fruit on it, which is just starting to ripen. I had three cucumber plants in buckets but they were out of control, so I have moved them out into my main garden…

I love the huge variety of delicious food in Japan, but it was a pleasure to return home and get back to eating salad, fresh from the garden. This year I am consciously trying to garden with more planning for succession, ie staged replanting salad items like lettuce, radish etc so I always have another lot of young plants coming up as the older plants start to die back.

So thats about it for my tunnel house. I look forward to using it throughout winter, and already have plans to get another one next year. It is the most intensive way to utilise a small area of land, and has been a great long term project.





6 thoughts on “Tunnel House project

  1. George Lavich

    Very nice read. I have a bucket list which includes a tunnel house. After reading your blog I will add Repath to the list
    Thanks for posting.

  2. Piotr Jasica

    Exceptional and relevant. I’m looking to build something functional and this is just perfect. Thanks for sharing.

  3. Terry Kyle

    Just completed a 6m Redwoods and then find this blog…….. sooo very cool, love the irrigation ideas, the acorn has been planted in my head.

    1. tim Post author

      I am just in the process of building second tunnel house – I got a 6m one this time too, although planning new one to partly be an outdoor/indoor lounge 🙂

    2. tim Post author

      Another option for irrigation would be a drip system – saw these at Mitre10 and they looked like a great system for watering roots & getting less humidity that way… I think I’ll use a dripper system in new tunnel house as it will have less plants and potentially bigger (eg tamarillo, mandarins etc) all in large pots… so a dripper into each pot should work well…

      Hozelock Easy Drip Irrigation Universal Kit

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