Topic: What temp should a greenhouse be kept at overnight?

[Zed42]

Hiya,

As you can tell from my recent question on min/max thermometers, I am a bit "green2 about all of this :)

I have purchased a greenhouse heater to keep my seedlings cosy overnight .. but how warm do they need to be kept? I've set it for about 10 degrees tonight, but is that overkill / not enough ?

Currently snowing here in Shropshire .... brrrr.....

[Trevor_D]

It depends what seedlings you're growing and how established they are. We set ours for about 5 or 6 degrees, but the thermostat doesn't seem that accurate anyway. We find you have to fiddle with it over several days.

Is the greenhouse itself insulated? Are the seedlings protected with fleece or something similar? I've built a heated bench with a soil-warming cable in it and we put the most vulnerable seeds & plants there.  The greenhouse at the allotment has neither heating nor insulation and although I haven't dared tiny seedling there yet, the more mature stuff seems happy enough. (Mind you, I did drape fleece over them the other day!)

Hope this helps. Someone who knows more about it will come along before long.

Trevor

[Tee Gee]

I agree with Trevor it depends upon what you have on the go and at what stage it is.

As a rule of thumb seedlings can stand a drop of around 10*F after germination and a further 10*F if the plants are more mature.

The key thing (in my opinion) is the watering!!

If the plants are wet this substantially reduces the temperature at root level, wheras if they are relatively dry ( what I call the damp side of dry) the roots can be 5-10*F warmer than the ambient (surrounding) temperature.

This is why some plants can survive a brief spell in below freezing conditions.

This is a write up on my system which I have developed over the years.

http://tinyurl.com/3ca7gw

[Two Choices]

Tee Gee, I've got my toms (about 10 ins tall) and Chillies (about 6 ins) on my heated bed which I have converted into a mini greenhouse with bubblewrap. Do you think I could turn the heat off yet? or should I remove the bubblewrap and keep the heat on for a while longer.
Also, have just pricked out my begonias and they are in another heated frame. What is the minimum temperature I should let these go down to. Thanks TC ???

[tim]

While replying to your other question, may I chip in here too? TG can always put me right!!

What temp is the bed? Once germinated, toms like growing on at 60F. Chillies mabe a bit warmer? Don't know.

But 10" Toms - for a heated greenhouse??  Far too soon for a cold one.

I like your post above, TG.

[Tee Gee]

Do you think I could turn the heat off yet?

Two questions;

1) Why switch it off??

2) Can the temperature be adjusted e.g lowered?

My view with a cable is;  the cost of leaving it switched on is minimal, particularly if it is thermostatically controlled, i.e. it will switch itself off/on as necessary.

If I recall correctly my 80 ft cable burns at 80 watts per hour, I think a 40ft cable is about 40 watt so when you compare that with an electric light bulb or the TV on standby I don't consider this much.

I would be rather upset if my economy excercise caused me to lose all I have strived for.

Answer knock the TV off standby and leave hotbed on!

[Two Choices]

TG, It's only 95w so costs less than 24p a day. I don't have a thermostat and with the warmer weather I am thinking of cycling it one hour on and two off during the day and then leave it on all night.  Was only thinking of trying to do my bit for the environment, but as you say, to lose it all now would be a great loss.
Can I just say a big thanks for the knowledge you and the other allotmenteers share with newcomers like myself. I'm sure it has saved some serious heartache.  :) :)

[Tee Gee]

What I have done before now is use a progammable power plug set to switch on/off as I wanted.

Admittedly I used it for lights not my propagator (it looks after itself)

Beats running up to the greenhouse every few hours.