Grow Your Own Magazine

This is the first year I've had a greenhouse, so I'm on a learning curve! I seem to have done ok so far but one thing I can't really find an answer for is 'how hot is too hot'? I keep reading of people saying they left their greenhouse doors open on hot days etc but how do I know when I should do that and when I should keep the heat in (short of fatal experiments! )?

I suspect there isn't a definitive answer but any help would be greatly appreciated.

Claire

I have my auto vents set to open at about 20C, but have been opening the door in the morning (every day) as well for a couple of months now.

You really do need to invest in a thermometer with a Maximum and Minimum reading. That is the only way to know how hot it is getting.

Plants that we commonly grow in the UK are not unlike ourselves - they like it in the 20's (degrees C, I mean). When it gets into the thirties, some of those which are actually from warmer climes - aubergines, chillis, melons, cucumbers etc - still enjoy it but it's getting too hot for some. Tomatoes, for example, start getting uhappy and by 40 degrees, their pollen will fail.

It is not difficult for a greenhouse to get into the upper thirties in the UK even with all the doors and vents open, so it is something you need to be aware of.

How hot it will get in the greenhouse depends on its location, its size (smaller often hotter) and the amount of airflow you can get. You have to manage this.

Get a thermometer and start looking at it - that is honestly the best thing you can do.

Thanks srodders and Cutecucumber. The thermometer thing makes a lot of sense. I have an ordinary one in there and it's been hovering around 30 a couple of times but of course unless I check it constantly, I don't know the max and min I'm getting. I shall buy a 'proper' one right now and try and keep temps reasonable.

"Around 30" is similar to temperatures I'm getting with windows and doors open. There's no way I can keep mine from getting up to 38 degrees in the really hot weather, but net shading and damping down regularly with water inside stops it getting into the 40's. Chillis and aubergines seem to love it, that's the good thing!

Cutecumber, I agree with you - keep the door and the window open if its hot - spray the floor with water if it gets hotter, paint the windows with windolene (only coz Ive got some left!), put greenhouse shading up as well........must go and check mine right now! Bernie

__________________
Appreciate the little things in life because one day you will realise they are the big things

My vents open at around 14c but the doors are open all day ( and if it stays around 10c all night as well). Heat itself isn't so bad it's the high humidity and poor airflow that causes the trouble giving rise to fungal problems

__________________
ntg

Never be afraid to try something new.
Remember that a lone amateur built the Ark.
A large group of professionals built the Titanic

http://grief-encounters.blogspot.com/

I had a fungal problem in the tunnels last year Nick caused by planting too close, the tomatoes went down with athletes foot and didnt do well at all.

As Nick says, its all about air circulation and controling humidity.

__________________
Kindest regards, David.

http://pigletsplots.blogspot.com/
updated lots - Sunday 28th at 1640hrs

My greenhouse stays open day and night (unless a frost is forecast) from early May. Still gets hot in there but it's sited so that after midday it gets dappled shade from a neighbour's large tree.

__________________
Earth laughs in flowers. Ralph Waldo Emerson

www.vegheaven.blogspot.com

Updated September 29th - Bean drying.

Mine is shaded in the afternoon by a vine outside the greenhouse which helps and has auto opening vent and top window. Net shading also. Don't open the door much at this time of year but seem to get away with it cos of where it is placed.

__________________

Some of us live in the past, always talking about back then. Some of us live in the future, always planning what we are going to do. And, then there are those, who neither look behind or ahead, but just enjoy the moment of right now.

Which one are you and is it how you want to be?

I have a 6x8 foot greenhouse with auto opeing roof and sidevents. The roof one sticks a bit and opens at around 23C . On sunny days which are warm I open door 5-10cms.. max temperature inside about 30C with a breeze.

On really hot days, open door completely.
I water 7am and cover floor : on really hot days pm as well.

Currently brewing nettle compost in old washing up bowl in bench in greenhouse (covered in clingfilm.. see if it speeds up process. ).
Have to be careful of open door as once caught a robin on flypaper and it died of heat?

What are the symptoms of athletes foot

thanks
marion

They can't RUN TO SEED!! SORRY, I couldn't resist

I have a small greenhouse (6x6) and the window has been wide open for weeks. I don't have an autovent so I'd rather they were cool than too hot. I've also taken to leaving the door open about 2" most of the time, night and day. It keeps the cats out but lets air in at the ground level. This has really helped pollonate the tomatoes and I've had near 100% success so much better than last year.

__________________
http://plot62.blogspot.com/

Im sure that somewhere Iread that in general plants do not grow in temps over 30 degrees centigrade - bound to be some exceptions, but not likely to be the ones youll have in the greenhouse.

Hello, Canna kid, and welcome to the Vine....

__________________
Hazel
www.hazelandjanesallotment.blogspot.com
update Sat 04/10/2008......sorry, Keats......

Don't ask me - I'm at that age when I'm always too hot (except when I go cold!). Cardie on and off!

__________________
Earth laughs in flowers. Ralph Waldo Emerson

www.vegheaven.blogspot.com

Updated September 29th - Bean drying.

Hi Flummery, been there done that. As for greenhouses I would say that anything over 75 degrees is too hot.

Plants wilt with the heat but will usually recover. There is a point at which they reach 'Permanent wilting point' and from this there is no recovery!

__________________
My Majesty made for him a garden anew in order
to present to him vegetables and all beautiful flowers.- Offerings of Thutmose III to Amon-Ra (1500 BCE)