Saturday 16 March 2013

Tunneling (1)

The bitter NE winds fade and we can get back out into the garden and, although it is way too cold to be handling the plastic sheet yet, we can assemble the poly tunnel structure so that we are ready to throw the sheet over on the first warm day. Plastic sheet is easier to handle and to get taut if it is warm and supple.

We have decided to position the tunnel in what was the westernmost bay of the three-bay former hay barn. In this part of the world it is pretty near impossible to grow tomatoes out of doors, or anything tender, for that matter, so anyone who is anyone in gardening has a poly-tunnel. Everybody tells you this. Neighbours, friends, the lady in the local charity shop.... Everyone is also an expert and advice comes from every direction as soon as anyone gets wind there-of. Some of it we welcome and value, some we take with a pinch of salt.

The official instructions which come with this tunnel say that to get the plastic sheet taut you must dig a trench around the tunnel perimeter. Then you drop the sheeting over your frame and tread it down into this trench before back-filling with soil. The weight of the soil holds the sheet down taut. Our Mentor Anne and partner Simon, however, have played this game before (they used to have a 60 foot tunnel or two when growing organic salad crops commercially in a former life) and Anne tells us that the wind and weather will tend to wreck your plastic cover in 5-10 years and you will need to replace it. You do not want to be digging that trench again and again so it is more sensible to lay a big timber (a 5 by 2 for example) all around the perimeter, fixed to the ground-tubes by metal brackets. You then wrap the sheet edges round long wooden laths and screw these down to the timber, gripping the sheet and keeping it taut but making it easy to dismantle should you need to move the tunnel or replace the cover. Sounded good to us, so we have gone with this method.

We have also been advised that things can get very hot and humid in a tunnel, so that you risk cooking the tomatoes. It is best, apparently, to plant the tomatoes at the sides so that they never reach the hot sweaty apex - you do your more tropical stuff in the centre bed there - melons and cucumbers. More advice has us warned that placing the tunnel in the hay-barn bay, so that it is to the north of the big front garden trees and the barn wall, might mean we are a bit spare on bright sunlight, and this might affect whether we can ripen toms. However, here we stopped listening to a degree.

The barn bay is the most useful position and is, we think, open enough to the sky to be in full sun through July, August and September. If we do suffer any light loss then this might also mean less over-heating and, certainly, being snug in against the wall and the trees will mean that the wind and weather's tendency to shred the plastic will be reduced. Having made all these decisions we then found that just down the lane, one of the McG's also has a poly-tunnel in a similar position with its plastic held down by the wood and laths method and his has lasted 11 years so far except where his dog chewed through one panel (!). Ah well. We will live and learn and if it all goes wrong we will do it differently next time.

You can see from the pictures that we are well under way, with the main arches and now the diagonal bracing installed. This being the floor of a former hay-barn of great vintage (50 years?) it has soil as you might expect - the local subsoil with boulders compacted down into a pan by the passing of generations of feet, animals, carts, tractors and machinery thinly covered with rotted straw-bale debris and the peat turfs they all store in barns here to keep them dry. The local stoloniferous grass has also moved in to create that frustrating rat's nest of roots and stems which stop you swinging a shovel about. It is a wet bog-hole and has been a mush since we moved here, never seeming to dry out.

We decided to dig across the whole floor first to cut through the pan and get some drainage going, second to extract the stones and peat turfs and third to mix the layers and bury the straw mush and stoloniferous grass. This should help it all dry out and might give our tomatoes a better substrate in which to put down roots. We may have to import some top soil from the nearby bank (source of rusty fertilizer spreaders and current home of the horse drawn hay rake). We are hoping that once the cover is on the area should no longer get too wet. The eventual plans may involve a weed-proof membrane and plank-sided raised beds but for this season, while it settles and we are still 'learning' we will just tread some paths and plant into the dug beds in between.

One area of confusion remains. Generally these tunnels seem to have a door at either end to allow ventilation on hot days. This one came as a kit with only the one door, and only the bits for a door frame at one end. That is also how the display model in their yard is set up. We assume that users who require the 2nd door either bodge one themselves or pay extra for the 2-door version. Because our 'other end' is just the caravan 'site' we will probably bodge an opening frame and a removable panel which can be replaced with a chicken wire version in hot weather.

Part 2 of this story when I have some pictures of the finished tunnel.


Anne Wilson said...

It's looking good Matt, however your tomatoes will do best nearest the door, I'm rather assuming you are going for two side beds and a centre one. Tomatoes like a not too humid environment, they also like to be shaken when in bloom, this gives them a better fruit set. If you do find the barn wall is cutting out light you could paint it white, but I think you will be OK.

Matt Care said...

Yes, thanks for that. We are indeed going for a side bed on the orchard side and a central bed, using them as you say, but we might to staging in the 'right hand side' for seed trays etc.