Building our poly tunnel greenhouse . . .

We had designed our own greenhouse and already bought the posts, plastic and some other materials when we were invited to a “Be The Change” event at St Marys and we saw the poly tunnel idea on this related website http://transitionderwent.com/whats-on-2/poly-tunnel-bulk-purchase/

We adapted the design to suit our garden as we are building on a solid slab of granite with only a few inches of soil.  We bought the poly tube from Becks in Launceston for $2.55 a metre.  It was on a 100 metre roll which was too large for our ute and had to be delivered by truck, cost $30.  We are using the remainder for a net enclosure for our orchard. I will post photos of that project when it is complete.

After laying out the position of the star pickets we couldn’t bash them in and had to drill into solid rock with a masonry bit.  This took all day, plus 20 Anzac biscuits and several cups of tea!!!  There are eight arches altogether giving us 10.5m in length and 4m wide, 42sqm in total.

Once the pickets were in place we made three raised beds from recycled roofing iron to hold the posts in position. This was easier and more eco friendly than concreting them in place.  The beds not only hold the posts but provide weight to stabilise the frame in strong winds.

We cut the tubing into seven metre lengths and pushed it down onto the pickets, this is a two person job, but was fairly easy to do. Instant frame!! We were very impressed with the strength of the frame already, and we hadn’t even put the timber bracing on.  You could use this frame for many applications and Nev is planning structures all around the place much to Bryon’s disgust.

This shot shows the bracing.  We have used 75x38mm pine for the side rails that was left over from another job, and 90x45mm merchant grade pine for the top rail.  We decided to use some brace strapping to hold the pipes to the posts as this gives a seamless outline for the plastic and the top rails on their sides will provide ample places for hanging pots.

After we had finished the frame we painted it white using left over paint given to us by a friend (thanks Tim).  We did this to reflect the sunlight from the black tubing and metal straps so it stays cooler and doesn’t affect the plastic over time.

The next step was putting the plastic on.  A 25m roll of poly-tunnel plastic cost $208 from Waratah Distributors in Launceston.  It is 7.5m wide to suit the 7m arches and is made from a UV stable non-rip plastic. It is important to get the right plastic as some tear very easily and also break down rapidly in the sun. Some I bought for a cold frame previously only lasted one season.  The supplier indicated this stuff should last at least five years and it is very hard to tear.

Putting the plastic on was by far the hardest and most time consuming part of the job.  Stretching it over the frame was easy but bringing it round the ends and making it a neat job took all day.  We made a bit of a frame and hung an old flywire door each end to provide ventilation and to keep the wildlife out.  The doors are made from Huon Pine which was salvaged from an old pub in Adelaide.

The finished job!!!  It was way too hot inside from day one and we have had to put a 1.8m wide strip of 70% blockout shade cloth along the roof inside to reduce the heat.  We barrowed in two year old fennel and mint mulch from a nearby farm and the tomatoes are going mad in there.  We have also moved our frost tender geraniums in and they are thriving on the heat.  We have lime, lemon and cumquat growing inside also.