I have just come back from digging 56 feet of trench around my newly erected polytunnel frame (bought 2nd hand) and am aching rather.
My trench is currently 18 inches wide and 9 to 12 inches deep. I still need to tidy the bottom of the trench and would guess that I will go down to 15 inches.
WILL THIS BE BIG ENOUGH?
This site is rather exposed.
Thanks for any advice (my copy of Gardening under plastic has gone missing so I can't check in there!)
how deep to bury poly tunnel plastic
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pigletwillie
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Thats about the size First Tunnels reccomend in their brocure.
Kindest regards Piglet
"You cannot plough a field by turning it over in your mind".
"You cannot plough a field by turning it over in your mind".
ours went in about 4 inches, any deeper would need a pneumatic drill, but we have let the grass grow back to help hold the soil together. we have had no problems with the wind except a couple of holes from unidentified flying objects.
Those are correct measurements but make sure that it is rectangular section not rounded for maximum keying.
I sent the following to the editor, it may interest you.
>I aggree with John Wosnip (March issue letters)about the usefulness of saving the water from polytunnels but in my case it came about as a necessity. Sixteen years ago in 1990 when we got our first polytunnel and installed it during the wetter part of the year according to instructions the accumulation of water both inside and outside the skirt turned the contents into a bag of slurry in a well lubricated clay-type trench so the gales had no difficulty in tearing the plastic cover out. Subsequent to that in all four major polytunnels we have used a standard method which has proved itself reliable in strength and effective in supplying a large part of our water needs. The trench is square section, no less than 15 inches wide and 18 inches depth. When the plastic cover is laid in it is tethered at both ends then the drainage pipe is laid in the bottom. Now one person sits on the outer part of the plastic and presses down on the empty pipe while the other pours pea gravel in to cover the pipe generously. The weight of this fill is sufficient to tension the cover. When the whole trench has been done the excess skirt is folded in to cover the pea gravel and an upper layer of stone pebbles or chippings is added to fill the trench and provide extra weight. By using gravel and chippings instead of soil we find it is very much easier to clear the trench when the time inevitably comes to replace the cover. In our opinion if one filled the pipe with chippings, and soil inevitably washed into it then it would be very difficult to remove the pipe and clean it out.
The drainage of our four main tunnels is conveniently connected together and fed into large storage tanks further down the hill
Regarding energy for an electric pump from our experience I would advise against using a wind generator as during the summer months in the hottest dryest weather we have anticyclones which means that there is the very minimum of wind, certainly not enough to supply electricity for the pump. We now have solar panels, not cheap but neither are wind generators, but most pumping is powered by our Honda petrol-driven generator into storage tanks at the highest point of our gardens. An underground pipe network supplies it to taps and water butts strategically placed in the tunnels.
Allan
I sent the following to the editor, it may interest you.
>I aggree with John Wosnip (March issue letters)about the usefulness of saving the water from polytunnels but in my case it came about as a necessity. Sixteen years ago in 1990 when we got our first polytunnel and installed it during the wetter part of the year according to instructions the accumulation of water both inside and outside the skirt turned the contents into a bag of slurry in a well lubricated clay-type trench so the gales had no difficulty in tearing the plastic cover out. Subsequent to that in all four major polytunnels we have used a standard method which has proved itself reliable in strength and effective in supplying a large part of our water needs. The trench is square section, no less than 15 inches wide and 18 inches depth. When the plastic cover is laid in it is tethered at both ends then the drainage pipe is laid in the bottom. Now one person sits on the outer part of the plastic and presses down on the empty pipe while the other pours pea gravel in to cover the pipe generously. The weight of this fill is sufficient to tension the cover. When the whole trench has been done the excess skirt is folded in to cover the pea gravel and an upper layer of stone pebbles or chippings is added to fill the trench and provide extra weight. By using gravel and chippings instead of soil we find it is very much easier to clear the trench when the time inevitably comes to replace the cover. In our opinion if one filled the pipe with chippings, and soil inevitably washed into it then it would be very difficult to remove the pipe and clean it out.
The drainage of our four main tunnels is conveniently connected together and fed into large storage tanks further down the hill
Regarding energy for an electric pump from our experience I would advise against using a wind generator as during the summer months in the hottest dryest weather we have anticyclones which means that there is the very minimum of wind, certainly not enough to supply electricity for the pump. We now have solar panels, not cheap but neither are wind generators, but most pumping is powered by our Honda petrol-driven generator into storage tanks at the highest point of our gardens. An underground pipe network supplies it to taps and water butts strategically placed in the tunnels.
Allan
Hi VG
The answer is YES. I've covered my small (15ft by 10ft) tunnel four times using a trench the same depth as yours i.e about 9 inches. They have survived even the near hurricance force winds we have had on three occasions. Wait for a still and reasonably warm day and put the cover on - here in N. Scotland this usually means waiting until mid April.
The last time I re-covered I considered putting in drainage as Allan suggests but didn't have the time. It's not been a problem over the last 5 years.
Good luck
The answer is YES. I've covered my small (15ft by 10ft) tunnel four times using a trench the same depth as yours i.e about 9 inches. They have survived even the near hurricance force winds we have had on three occasions. Wait for a still and reasonably warm day and put the cover on - here in N. Scotland this usually means waiting until mid April.
The last time I re-covered I considered putting in drainage as Allan suggests but didn't have the time. It's not been a problem over the last 5 years.
Good luck
Chris
allan have i read your post correctly? the plastic from your cover crosses the bottom of the trench and up the outer side to form a channel to collect the rain from the tunnel cover? ours only covers the bottom of the trench so runoff from from the cover soaks away into the surrounding soil.
Chris, a lot depends on type of soil, worst is clay, size of polytunnel, the exposure of the site. Better safe than sorry. If you have stood by helpless while you tunnel cover is destroyed by the force of the wind you would take the maximum precautions possible.
On none of my Commercial Tunnels have I buried any Polythene. I have a gravel board fixed at ground level and the polythene is wrapped round 2"x1" batten and screwed to the gravel board. They have never been any scource of difficulty and it is an easy job to tighten the skin if necessary.
Because I was having a difficulty with ventilation I modified them and fitted a rail 3' high and now the polythene terminates at this height and I have Anti White Fly netting around this 3' skirt. In order to maintain some heat during the winter a thin guage polythene is affixed over the Anti White Fly netting and remove as necessary. I have six tunnels and they are all 60'x30' and they have been in operation since 1993. For the record most of them are still on the original polythene so the method cannot be without merit.
Because I was having a difficulty with ventilation I modified them and fitted a rail 3' high and now the polythene terminates at this height and I have Anti White Fly netting around this 3' skirt. In order to maintain some heat during the winter a thin guage polythene is affixed over the Anti White Fly netting and remove as necessary. I have six tunnels and they are all 60'x30' and they have been in operation since 1993. For the record most of them are still on the original polythene so the method cannot be without merit.
JB.
Johnboy, what happens to the drainage from the tunnel?. I considered a modification along those lines but with the sloping sides to my hoops the rain would just spill onto the ground just inside the tunnel which is at times very undesirable besides wasting the rain uncontrollably. I had to accept this rain on my mobile tunnels and am currently overhauling a black polythene skirt addition to cure excessive waterlogging by shedding the rain out to an added trench.The fact that these tunnels are sideways on to steeply sloping ground exacerbates the problem. What size is the gravel board, it has to take the tension of the plastic without warping or breaking and there has to be a method of tensioning the cover which in my case is applied by the weight of the infill as the trench is filled. There is some slotted aluminium rail with a locking bar insert available but that was ruled out on cost. It seems to me that there must be a compromise of something, I can't see an answer that is ideal and affordable.
Hi,
My tunnel is 14ft x 28ft. I have managed to dig out one long side, one short side and half a longside. So just half a long side to go!. I am fitting a 4 ft door and 4 ft ventilation at the other short end, so only a small amount to dig out there. I am also putting 8 ft of ventilation at the other short end, but I had dug the trench before realising I did not have to!
Your water collection sounds great, fortunately my field has a 100 meter elevation over 600 meters with a spring at the top, already tapped into and supplying a water trough halfway down. I have piping and connectors to run the water down to the veg area near the bottom (closer to the road to save walking!)
I will certainly put drainage pipe, stones and gravel in the bottom to weigh down the plastic. my soil is clay and I take your point about it slipping in wet conditions. I have a nice pile of stones collected from the ground, varying from a few inches to 2 foot! Will probably need a lot more though...kids join the chain gang!
Thanks for all the advise
Vivianne
My tunnel is 14ft x 28ft. I have managed to dig out one long side, one short side and half a longside. So just half a long side to go!. I am fitting a 4 ft door and 4 ft ventilation at the other short end, so only a small amount to dig out there. I am also putting 8 ft of ventilation at the other short end, but I had dug the trench before realising I did not have to!
Your water collection sounds great, fortunately my field has a 100 meter elevation over 600 meters with a spring at the top, already tapped into and supplying a water trough halfway down. I have piping and connectors to run the water down to the veg area near the bottom (closer to the road to save walking!)
I will certainly put drainage pipe, stones and gravel in the bottom to weigh down the plastic. my soil is clay and I take your point about it slipping in wet conditions. I have a nice pile of stones collected from the ground, varying from a few inches to 2 foot! Will probably need a lot more though...kids join the chain gang!
Thanks for all the advise
Vivianne
Good luck with it all. Actually my tunnels are in Wales just outside Monmouth. None of my tunnels have the ends buried, just fixed to timber there but I have to admit that we have had to stop the rabbits etc. trying to get under the plastic there. Lucky you with the spring. We have a stream at the bottom, 2 fields away which is too far, other than that it is mains water if not rain.
Allan
Allan
Hi Allan,
If necessary to collect water with the rail 3ft up you can fit a gutter just under the batten holding the polythene but I do not use rainwater as my water supply is free of all the chlorine and other additives added to the normal mains.
My supply comes from the Elan Valley Aquifer that feeds Birmingham and is only treated by a filter and Ultra Violet filter. At my pickup point for water it is 310 ft below the Resevoir outlet and the pressure is incredible.
If necessary to collect water with the rail 3ft up you can fit a gutter just under the batten holding the polythene but I do not use rainwater as my water supply is free of all the chlorine and other additives added to the normal mains.
My supply comes from the Elan Valley Aquifer that feeds Birmingham and is only treated by a filter and Ultra Violet filter. At my pickup point for water it is 310 ft below the Resevoir outlet and the pressure is incredible.
JB.
Our supply at the farm seems to be high quality, we take it home for drinking purposes as it tastes much better than the Hereford river water and as I said before we don't pay the sewage levy at the farm. It may be coming from Elan valley too. I wouldn't like the complication and expense of fixing the plastic and at the same time fixing a gutter under its edge.There was something like this in the magazine a while ago, I couldn't see enough detail in the pictures to see what he had done. We have automatic vents in all the doors so the summer heat isn't all that of a problem. The prevailing wind hits the tunnel lengthwise.
Allan,
It's not the slightest bit complicated and I can tighten a 60ft tunnel in less than an hour from start to finish on my own. The board at 3ft high is 4inches wide and the gutter brackets fit under the batten very easily and the edge of the gutter is under the batten and all the water falls direct into the gutter nothing could be more simple.
If I were going to bury my polythene I would use Pea shingle as the backfill material as it is then much easier to remove if necessary. Coupled with as you have described the way you place your polythene to form a drain. I would think that this would be the ideal drain.
As for ventilation well my tunnels were not used for the same purpose as yours and the tunnels were completely benched out which is very diferent to growing in the ground. Everything of mine was ether in module or pot which makes one hell of a difference.
For the record the prevailing wind should flow over the width of the tunnel and not down the length of the tunnel. This prevents the wind from buffeting the polythene during high wind periods. Polythene last one hell of a lot longer with the wind flowing across the width. I have a share in another Nursery and the tunnels are run with the prevailing wind down the length and a cover that was renewed last year has already split. The tunnels are now to be resited with the wind flowing over the witdth but would you beleive we need planning permission to do this. Knowing our council they probably will not give permission with their view on Polytunnels!!
It's not the slightest bit complicated and I can tighten a 60ft tunnel in less than an hour from start to finish on my own. The board at 3ft high is 4inches wide and the gutter brackets fit under the batten very easily and the edge of the gutter is under the batten and all the water falls direct into the gutter nothing could be more simple.
If I were going to bury my polythene I would use Pea shingle as the backfill material as it is then much easier to remove if necessary. Coupled with as you have described the way you place your polythene to form a drain. I would think that this would be the ideal drain.
As for ventilation well my tunnels were not used for the same purpose as yours and the tunnels were completely benched out which is very diferent to growing in the ground. Everything of mine was ether in module or pot which makes one hell of a difference.
For the record the prevailing wind should flow over the width of the tunnel and not down the length of the tunnel. This prevents the wind from buffeting the polythene during high wind periods. Polythene last one hell of a lot longer with the wind flowing across the width. I have a share in another Nursery and the tunnels are run with the prevailing wind down the length and a cover that was renewed last year has already split. The tunnels are now to be resited with the wind flowing over the witdth but would you beleive we need planning permission to do this. Knowing our council they probably will not give permission with their view on Polytunnels!!
JB.