Polytunnel watering & air flow during cold months

**marchogaeth** · 09-04-2015, 05:13 PM

How big is your tunnel? Is it a tunnel or a "blow away"? How much natural ventilation is there eg gaps round doors at the bottom of the sides? How wet is the soil 3cm below the surface? Does it feel humid?

I did start a more detailed reply but realised I was trying to cover all possibilities so more info please.

**planz** · 09-04-2015, 05:38 PM

9 meters long x 4 meters wide x 2.3 meters height
There is only one front door, 2 meters length x 1.50 meters wide.
Other then that the sides are well isolated with soil placed above polythene. So almost no air enters though other points.
overall, it looks something like this:
http://www.chilefoundry.com/wp-conte...olytunnel.jpeg

**planz** · 09-04-2015, 05:43 PM

Originally posted by marchogaeth

How wet is the soil would you say. The surface is likely to be wet from the condensation but below that?

The surface is wet due to heavy rains. So the water has come from below. If you look on the surface it looks dry, but when you dig a bit you can see slight humidity. Not mushy or sticky just dark looking soil.

**marchogaeth** · 09-04-2015, 06:05 PM

Sorry I didn't follow your original link.

You don't want your tunnel humid if you can help it (hot or cold weather), equally you don't want to open the door in winter and cause a draught. You only need to open the doors a crack to get some useful air movement if you feel the air is too humid. Obviously, with only one set of doors you might have to compromise a bit.

Condensation is part of the tunnel environment unless it's making the whole atmosphere really wet through the whole day.

I think I'm coming round to say, if the plants were in your garden and you would water them then water them in the tunnel. This is especially true of seedlings, where their roots are quite shallow. This last week has been crazy with temperatures reaching 38C even with both sets of doors open.

Through the winter I have lots of brassicas/leeks/beet growing in my tunnel and I probably didn't water more than once a fortnight on the beds against the walls. I water each plant not the soil. My middle bed is a bit drier so I checked the soil at 3cm and watered individual plants as needed. (I bury plastic bottles, with the bottoms cut off, top down in the soil to direct the water below the soil surface to keep the moisture level a slow as possible and to avoid growing green soil.)

Hope this helps at least a bit.

**unclefudgly** · 09-04-2015, 06:20 PM

I have vents that go all the across the polytunnel front and back, these measure about 18" from ground, just netting to keep butterflies out. I also have top half of my single door as netting, so plenty of ventilation. I have started to open the ground vents this week during the day as too hot in tunnel already.
I also have a 25% shade netting on sunny half of polytunnel which helps a lot.
Cheers

**planz** · 09-04-2015, 07:21 PM

Originally posted by unclefudgly View Post

I have vents that go all the across the polytunnel front and back, these measure about 18" from ground, just netting to keep butterflies out. I also have top half of my single door as netting, so plenty of ventilation. I have started to open the ground vents this week during the day as too hot in tunnel already.
I also have a 25% shade netting on sunny half of polytunnel which helps a lot.
Cheers

Pictures would have been great

**marchogaeth** · 09-04-2015, 08:02 PM

Net door as UncleFudge describes.

I've seen books recommend cutting vent holes along the length of the tunnel. I wouldn't want to do this as I think it would weaken the structure in strong winds - better to put a second set of doors in IMO. Some tunnels are designed with the vents in them so have the necessary strengthening or have netting along the length at floor level.

**planz** · 09-04-2015, 08:28 PM

Having fixed netting does not sound very good for autumn & winter growing. At least when you have doors or windows you can open/close them based on the weather.
I might be wrong though.

**WendyC** · 09-04-2015, 09:37 PM

Were the seeds sown directly into the soil or in seed trays in compost? Also where are you, as weather conditions vary hugely across the UK (and the world if not UK based)

**Bigmallly** · 09-04-2015, 10:07 PM

Oh Bagger................I'm so glad I came across this thread, I've just had to venture into the darkness as I forgot to close both doors on both tunnels............

............Thanks

**marchogaeth** · 10-04-2015, 09:04 AM

Originally posted by planz View Post

Having fixed netting does not sound very good for autumn & winter growing. At least when you have doors or windows you can open/close them based on the weather.
I might be wrong though.

Well many, many people use the half net door. As far as I can see, the net is quite fine and so breaks up all the bit the fiercest head on winds while providing ventilation. I've just got big gaps round the doors!* Maybe you have just got to run for a season with what you have got and then start making adjustments just like with a new garden.

*The gaps are deliberate, we often have 50-60 mph winds, the idea id that if the wind is really bad it's better to have it take the doors off than damage the tunnel frame. the most annoying wind id the one that sucks the bottom doors out on it's way past!

**unclefudgly** · 10-04-2015, 10:42 AM

Originally posted by planz View Post

Having fixed netting does not sound very good for autumn & winter growing. At least when you have doors or windows you can open/close them based on the weather.
I might be wrong though.

Hi, I attach a double piece of spare polythene to inside of the door to cover the netting in winter, its only attached at the top so still get some ventialtion which helps even in winter.

**planz** · 10-04-2015, 01:13 PM

Originally posted by WendyC View Post

Were the seeds sown directly into the soil or in seed trays in compost? Also where are you, as weather conditions vary hugely across the UK (and the world if not UK based)

Seeds were sown directly in well prepared soil in first week of March. Our climate is definitely different from UK though.

**planz** · 10-04-2015, 01:14 PM

Originally posted by marchogaeth View Post

Well many, many people use the half net door. As far as I can see, the net is quite fine and so breaks up all the bit the fiercest head on winds while providing ventilation. I've just got big gaps round the doors!* Maybe you have just got to run for a season with what you have got and then start making adjustments just like with a new garden.

*The gaps are deliberate, we often have 50-60 mph winds, the idea id that if the wind is really bad it's better to have it take the doors off than damage the tunnel frame. the most annoying wind id the one that sucks the bottom doors out on it's way past!

So you are saying it is sufficient to have small openings in both ends of the tunnel, so air can flow?

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