Greenhouse Temperatures

[David]

Hello all,

very proud to be the first to post here, hope its worthy.

I have two questions, one pressing and one worrying.

Firstly, it gets hellish hot in mine very quickly and I wonder what the optimum temp is in general and how you control it. I have an automatic opener but it soon gets overwhelmed. B&Q have shades I can buy but they are about £20. What is the prefered method out there?

Secondly, it gets very warm and moist in there, nice for plants and to sit but arent I risking fungus etc. Any advice or wisdom on that as I'm worried I'll catch some dread fungal disease.

Thanks

David

[arthur e]

Hi David I would suggest a range of temps between 10 and 30 degs will be OK, Greenhouse size and the amount of vents has a lot to do with temp,don't forget for the hot air to get out cold air needs to get in and mix with what is there, usually achieved by opening the door a bit or a lot depending how hot it is. You can get a brush on white solution to paint on the outside of the glass to reduce the amount of sunlight which is likely to scorch your plants.As for the fungus, if you have a good movement of air in the GH it won't be a problem.

[sandersj89]

For me I find the best way to shade the house is with netting. The paint on cool glass stuff is a pain to remove at the end of the summer and it is not a flexible option.

With netting, I have it on a roller so it is a bit like a roller blind, I can remove it for dull days and therefore can manage the light as required.

I wholeheartedly agree with ventilation being the key to heat control. Roof vents coupled with louvers lower down and great as both can be automated. I would love to come up with some way to automate the door opening as well.

I also use my fan heater in the summer to circulate air. It has a fan only option and an upper temp thermostat so it will come on when things get too hot. I dont like temps to get much above 30 degrees as this will stress most things here in the UK. An exception may be aubergines which seem to like it hot for best results.

HTH

Jerry

[Allan]

Ventilation alone won't save your plants. I have doors both ends. 8 roof vents plus automatic louvres below but the thermometer on the bench went to 50C and it killed a batch of seedlings. I have got to take external shading seriously and my knowledge of Physics says that one must intercept the sun outside and convert the ultraviolet to heat which then convects away harmlessly in the breeze, any shade inside is not going to stop the sun's heat once it has come through the glass.
Allan

[David]

Excellent thinking Allan. You are right the suns energy converts from short wave to long wave as it passes through the glass - long wave forms cant go through glass so the energy is trapped and the heat is the result.( I wonder why it dosnt get brighter in there too.....)

So you are exactly right the shading needs to be on the outside, prior to the energy conversion.

Thanks, David

[loznkate]

Hi All,

Just a thought. What about tin foil stuck to the panes. Shiney side up, it would reflect most of the electromagnetic radiation (regardless of wavelength). I've not tried it. You can get big catering rolls for a few quid

I didn't shade mine last year and everything was fine even tho its in direct sunlight nearly all day. That said its polycarbonate so its translucent. I've just acquired an additonal glass one this year so shading might be more of an issue.

Might try the tin-foil and see what happens.

Regards.

Loz

[Allan]

tin foil (aluminium these days actually as tin is expensive) is fine in principle but I would opt for a more flexible approach such as aluminium a la venetian blinds or even a fabric with aluminium finish should work as well. I do know from experience that the tape wit aluminium finish e.g. Elephant Tape disinteggrates rather quickly in the sun and you are left with the mesh reinforcement. Methinks a white surface would function almost as well and might be easier to come by. It raises the topic of what is Gardening and what is Physics, Chemistry, Engineering, Mathematics, Computing, Hydraulics etc, you find very many disciplines involved, not just the horticulture.
Allan

[loznkate]

Allan,

If its not a combination of all you quote then its nothing.

Loz

[richard p]

both my 14 by 30 tunnels have stable doors at each end. normal practise has been to open the top half of the south end and leave the north end shut, opening both ends seemed to result in lower temp but the through flow of air means more drying out and more frequent watering required. this year i splashed out on thermometers, on sunny days they go off scale at 50 degrees. last saturday with both ends open they still exceeded 50. this weekend sweede , beetroot and runner beans have successfully germinated, also we harvested courgette , strawberries, cabbage, cauliflower, peas , spring onions, broadbeans and lettuce . both runner beans and french beans are in flower, i keep the soil moist to the touch, plants and seeds in pots are in trays and are kept moist (by watering cane from the bath outside) so i dont think the high temp is a problem, there is aways condensation on the inside of the plastic (unless the 2nd door is opened). i dont want to use shading to reduce the heat as tomatoes will suffer (so im told!) in the lower light levels.
general watering is done nominally once a week for an hour approx with an ordinary rotary lawn sprinkler mounted about two foot above ground level (4 moves completes both tunnels on a sunday morning) if its really hot weather an xtra half hour sprinkle one midweek evening keeps things moist. compost and fresh lawn mowings are added occasionally to help retain moisture. the chickweed , groundsel and dandelions are also thriving

[meya]

I bought some nice shades from here http://www.thesewingdirectory.co.uk/bus ... linds-uk-1 . They are cellular. Really good. About moisture...what can I say...there should a solution for this too.

[Primrose]

I can only add here that for years I've felt very frustrated at not having sufficient space in our garden for a greenhouse (only one of those 4 shelved mini plastic covered things) but on reading through this thread I've started to realise that there's no such thing as a free lunch and that they can, in fact, end up being quite problematic as soon as you start to experience extremes of temperature, especially in very hot weather. Perhaps I should stop being envious and just be grateful that I'm not having to grapple with an extra set of problems whenever we have a heatwave.