Greenhouse ventilation for tomatoes

[jayjaybee]

I have a 8x6 glass greenhouse which I plant up with mainly tomatoes. I have suffered from tomato leaf mould for the last two seasons. Ventilation is stated as being a deterrent for the mould. My question is at what overnight temperature does the forum recommend leaving the greenhouse door open. I have always kept the door closed overnight to keep the temperature up, but I might be causing the problem of mould by doing this.

[Pa Snip]

Have only ever grown max of 4 toms on one side of my 8 x 6.
Since I don't grow them early in the year I don't have issues about leaving door open. In fact, once we have external temperatures of 10 or above the door and roof window are left open to allow air flow.

Always held view, better later crop than total failure due to disease.

[tigerburnie]

I will have automatic openers on my two roof vents and I also have side louvres, so the doors will always be shut at night to keep out unwanted rodents etc.

[jayjaybee]

How interesting gardening is, we all have such varied views. This coming season I'm planning on leaving the door open on nights when it's likely to be above 10, I might be a little less greedy and stick to 4 plants a side, rather than a cramped 5 or 6. I'm also investing in a hand steam cleaner to hopefully sterilise the structure's nooks and crannies. Time will tell whether I've beaten the dreaded tom leaf mould. I will report back later in the season.

[robo]

I don't normally leave the door open on the pollytunnel but at the top of each door there is a mesh which gives good ventilation in the colder months I just cover it with visqueen

[Westi]

I don't put my Greenhouse Crops in there until I know I can leave the door open, if I do get caught out with a colder snap I will close it but leave the vent open (& throw a fleece over the plants if it is going to be proper cold). The only reason I do this is so I will still have some air movement in there if I forget to open the door in the morning before going to work, the door doesn't quite meet at the side either which also helps. (I put a chestnut under the frame to ward off spiders but it worked up & buckled the frame a wee bit - & didn't work with the spiders either)! I like the idea of steam cleaning the nooks & crannies, great idea!

[jayjaybee]

The crops/seedlings are all in the greenhouse, sometimes it's like a jungle with all the bedding plants seedlings and tomatoes vying for space. I use propagators and a frost thermostat controlled heater earlier in the year, but I'm not certain at which stage the mould takes 'root'. Don't praise me too early for the steam cleaner, I haven't bought it yet (on offer at Aldi next Thurs) I'm hopeful but not confident. I might melt the glazing beading and cracked the glass for all I know! But it'll definitely kill mould spores.

[Westi]

It will be fine I should think, but like you say comes with risk! But I had one & have silicone beading in places around drop in appliances & no damage. I think the only risk will be the glass will be cold & there will be a change of temp - is your greenhouse heated as that would make it more even.

[Monika]

Jayjaybee, I use a combination of the above suggestions: we also have a 6x8 greenhouse and grow tomatoes but also other vegetables and flowers. It has two top and two bottom ventilators as well as the door of course. One of the top ventilators is automatic, the other manual. All of the ventilators have fixed 1" mesh and the sliding door also has a swing door with 1" mesh, to try to keep out birds (we have had a robin's nest in the past and house sparrows kept getting trapped). I must admit I ventilate a lot, certainly when temperatures reach, say, 10C in the night in summer and almost all day in spring, summer and autumn. The greenhouse gets a lot of sun, so traps the heat even on a sunny early spring day which would keep being released slowly over night.
By the way, even now, with herbs and lots of spring bulb, primulas and violas in the unheated greenhouse, the door is open all day and the top ventilators slightly, in order to provide a flow of air.

[tigerburnie]

I can get a frost or snow in June up here and again come September, if I still lived in the Midlands I might have a different idea. I have an 8 x 12 house and will have at least 15 plants in there, so I will need good ventilation, but the doors will be closed unless we get a heat wave.

[jayjaybee]

It will be fine I should think, but like you say comes with risk! But I had one & have silicone beading in places around drop in appliances & no damage. I think the only risk will be the glass will be cold & there will be a change of temp - is your greenhouse heated as that would make it more even.

House is empty at the moment, hence the cleaning. Have bleach cleaned the roof area with toothbrush, I'm hoping the steamer will prove easier, I think I will have to take care on the glass. Although we're in the south we had snow all day today, luckily it didn't settle. Far too cold for outdoor work.

[sally wright]

Dear Jaybee,
I think ventilation top and bottom is essential, but the other thing you can do to reduce moisture overnight is to water in the mornings. This allows any surplus water on the leaves and other surfaces to evaporate out of the glasshouse before the humidity starts to rise overnight as the temperature falls.

The drier you can keep the leaves the more chance you have of reducing mould. If it gets really hot (in Britain?!? who are we trying to kid!) then damp down the floor to increase humidity rather than the plants.

If you are using water from a butt on your tomatoes do not get this on the leaves; this is a significant source of infection because the spores of many fungal pathogens of leaves can survive in water.

Once the top truss fruit has reached full size then reduce the amount of water by about a third. As well as reducing the amount of mould this will do two things. One, it will avoid a lot of splitting fruit as the weather starts to cool and the days shorten because the plants do not need so much water and two, it will improve the flavour of the later fruit as it increases stress to the plant.

If tomato plants are over watered there are two ways to tell visually. The first is fruit splitting and the second is called guttation. If you look carefully in the mornings you might see a row of water droplets along the edges of the leaves. They look very symmetrical and are nearly all the same size. They are caused by water pressure simply forcing it's way out of the leaves. Two other plants which can do this are Zantedechia and Fuchsias.

I hope these extra tips help.
Regards Sally Wright

[jayjaybee]

Many thanks Sally all good advice for when the warmer weather arrives. Hopefully with all these tips I will win the mould wars.

[tigerburnie]

Sound advice Sally

[Tony Hague]

I find this discussion slightly surprising. We are talking about cordon tomatoes here are we ? I have a greenhouse of similar size, and fit in ten plants on one side. I use a ring culture method, with the plants maybe 14" apart, in two slightly staggered rows. I guess this is the upper limit, but I haven't had fungal problems except for botrytis late in the year, which is pretty common I guess. I do have an auto vent, and have a hook to hold the door ajar in hot weather. The advice of 10 degrees minimum for tomatoes seems pretty unanimous. One more thing - I used a sulphur candle one year, never again. Sets all metal parts and fittings corroding, including the vent opener !