[stainesbloke]

Hi....I have put up one of those allotment polytunnels on my plot recently and planted it with tomatoes, sweet potatoes, peppers and lettuce. I'm a bit concerned about the massive amounts of condensation, however which drips onto the plants. I know this encourages blight/botrytis. Should I be leaving the vents open all the time? I don't at the moment because its gone chilly. When I have done before the condensation disappears very quickly.

[agapanthus]

I suppose it all depends on the weather...if it's warm keep them open, if it's cool close them.

[shokkyy]

According to my How to Grow Food in your Polytunnel book, you should always open door and/or vents in the daytime, even in the middle of winter. If you have something tender in there that needs protecting from cold temps, then use fleece or something to protect it. But if you don't open the doors and vents you will get too much condensation and that will lead to mould. What I tend to do is open the door always in the daytime, but open the side vents only when it's not too cold.

[sunshineband]

According to my How to Grow Food in your Polytunnel book, you should always open door and/or vents in the daytime, even in the middle of winter. If you have something tender in there that needs protecting from cold temps, then use fleece or something to protect it. But if you don't open the doors and vents you will get too much condensation and that will lead to mould. What I tend to do is open the door always in the daytime, but open the side vents only when it's not too cold.

Good advice shokky 

Also, if the wind is blowing straight into the door, open some vents or the tunnel might take off

[3759allen]

I open my vents when during the day when it's hot. if it's not hot for a day I just leave it, check what the temp is every so often and open for a couple hours.

if they don't get opened for a day or two it's no big drama's, any longer than that and you need to just bite the bullet and give it a good airing with the vents open all day.

it's not often you'll get a day in summer with no sun at all, mine warms up so quick that just an hour or so increases the temp no end, enough to make it viable to open the vents.

[Eblana]

As I can't get to the plot every day to open the doors/vents on the PT I have replaced the plastic in the doors with debris netting which allows enough ventilation in to stop the condensation without it getting too cold.

[grinling]

polytunnels are too hot for lettuce as they prefer cool, but in autumn plant round lettuce in the polytunnel for overwinter,

[3759allen]

i hate to disagree but i tried lettuce in the tunnel (mainly as a bit of an experiment) and they absolutely love it, even when it's been a bit too hot.

infact i think i'll be keeping a little row in there all year til it gets too cold. they grow alot quicker than the ones out side so if i can see there'll be a gap between the crop outside i can get some planted in the tunnel to try and fill the gap.

[shokkyy]

I've got a gorgeous row of lettuces in my tunnel right now

I grew them in the tunnel all through last year, as I tend to do most leaf crops, because they're absolutely perfect when I grow them in there, no nibbles or weather battering. I've got chard and spinach with leaves the size of rhubarb in there as well. They are bolting now because they're last year's plants that have stood there all winter, but they've been keeping us in lovely greens since last summer.

[Beetroot queen]

I grow lettuce in our tunnel space between feb, march till about July and then they seem to struggle.
They go under a net tunnel outside and seem very happy.

[seaside]

The threat of botrytis with tomatoes etc is important. Last year I kept my greenhouse closed for all but the hottest one or two days, in attempt to keep out blight spores. Every morning I opened the greenhouse, one could see the roof condensation that had dripped onto  the plants. I ended up with botrytis and it needed a lot of management to get a crop.
So, this year I have adopted a different approach and am leaving the door open over night when temps are over 10 degrees... no reason in keeping it closed. However, if and when blight comes a knocking in our area, I will have to close the door for the duration I guess as it blows over. Difficult to tell sometimes the difference between botrytis and blight on tomatoes, but I think botrytis can be managed somewhat better than full blown blight.

[shokkyy]

Last year all my outdoor tomatoes were completely wiped out by blight, so I was very glad I'd planted some cordon toms in my tunnel. The doors and side vents were left open overnight whenever it was warm enough, and no blight ever affected the plants in my tunnel. They weren't far away from my outdoor toms either.