Polytunnels - Beginners problems

ron · Polytunnels - Beginners problems

Can anyone offer some advice please.
I have acquired a polytunnel frame 13ft wide and 40ft long, but am
unable to find constructive advice for the questions I have.
1. Is it better to bury the liner in a trench, or use a cladding
rail ? I am probably being thick, but I cannot grasp how burying the
liner will make and keep it tight.
2. The tunnel will relace a greenhouse I have had for this year only.
It was covered in polythene due to the prohibitive cost of
horticultural glass in this country. Due to poor, almost non-existent
ventilation, I lost everything to grey mould. My tunnel has stable
type doors at each end, and I have been advised to cover the top half
of each door with wind break netting, and leave them open all the
time.The bottom half of the door has to remain closed at all times as
we have a flock of wild peacocks, and, from bitter experience, I know
they eat everything. Is this wise, and what effect will it have on
temperature during the winter.
3. I am looking at an overhead spray bar for irrigation. Is this an
effective means of watering?

Sorry if the questions are a bit basic, but I want to try and get it right first time.
Thanks
Ron

chook

Hi Ron,

I'm by no means an expert and can only speak from our one-tunnel-experience but we went with burying the plastic in a trench. We got a second hand tunnel and I didn't even know about cladding rails then but if your site is in any way windswept my guess would be that burying is the better option.
We dug a trench about 50cm deep and the plastic has to fit all the way in and line the trench in a U-shape, i.e. all the way back up to the surface. The soil in the trench then holds and tightens the plastic.

re ventilation: sounds like good advice. unless you are around all the time and can open and close doors as required. I'm always for the easy/lazy option and our doors are fully done in the green netting. Then I don't have to panic about it getting too hot and/or humid. Of course in the winter you loose heat that way but maybe you could make full panels to hook into the frame for the winter?

re irrigation: overhead spray is fine except for tomatoes as they like to have 'wet feet and a dry head' as my boss used to say. So ground irrigation would be better if tomatoes are your objective.

If I was starting over I'd buy a tunnel wide enough to host a centre isle of large water-filled barrels. They heat up during the day, and release the heat overnight, thus moderating temperature extremes. The tops of the barrels could double up as 'tables' for seedling trays.

HTH
chook

blowin

Hi Ron, I am no expert either . Just a couple of thoughts to add to what Chook has already said :-
Trenching seems to be the accepted method around here . I am pretty sure that the cladding rail & accessories are expensive items . The main benefits of this system are that you can make frequent and big changes to the ventilation ( if you have the time ) , and/or insert vents ( if you can afford them ) .
I imagine both would be quite easy to DIY but believe there is also the need to set the ground fixings/bottom of the frame very securely eg in concrete . You don't have to do this if you trench . ( In fact , if your ground is very soft you may need to put a short cross-piece on the ends of each hoop to stop them from being pushed deeper by the tension on the poly ) .
My poly is 60 ft by 18 ft . The trench is about 12" out from the frame and it is about 15" wide and deep . It has , so far at least , withstood several gales which brought plenty of trees down .
When calculating the width of poly you will need for the trenching method , allow at least 2ft spare all round . In other words , poly goes over the frame , goes out the 15" to the edge of the ditch , down , across and back out of ditch , plus at least 24" spare on each side . You will need this to get a decent hand-hold when you are back-filling the ditch . That is the secret to getting a lot of tension on the poly .
It is generally recommended that the length of a polyTunnel should not exceed double its width , or you will get more than the usual number of complications with ventilation . ( Note the dimension of ours -- it is very easy to be wise after the event !!! ) . However , we haven't had any serious problems with damping off or mould . We just avoid planting tall things across the beds ( ie we make the rows run front-to-back ) so you don't create windbreaks , and tend to water the ground rather than sprinkle .
Poly-covered stable doors at both ends. We leave top halves open all day unless it is really cold .
We don't grow anything terribly exotic but the salad and veg yields are fantastic .
Personally, I'd settle for getting it right the hundred-and-first time
Laughing

. Good luck .

wayland

Damn!! My first attempted post disapeared. My last PT had a means to tension the cover after it had been buried. This was done by raising the frame out of the ground stakes and inserting a pin in the pre drilled holes provided in the frame. It is also possible to fit a winding mech that litteraly winds up the sides for ventilation. I`ll send you a sketch if you are interested.