How much heat?

I have all sorts of flower seedlings in the greenhouse now and my tomatoes. The 'flowers' will stand 5C overnight as long as it's not continuous..... a night here and there. Below that I cover with bubble wrap. Tomatoes will cope with 7C but keep an eye on them. So as a general rule 7C minimum unless you can cover them.

 

@Sheal will any type of bubblewrap do? I've been googling and seen horticultural bubblewrap which seems different than bubblewrap used for parcels. Also should it be big or small bubbles?

 

Thanks FC.

 

Fern......I'm just using parcel bubble wrap that I've had knocking around at home, it has small bubbles but it doesn't really matter what size as long as it gives some warmth overnight. I give the bubble wrap some support so it doesn't crush the seedlings, I had upturned buckets at each end of my shelving just to prop it up. Don't forget to uncover in the morning or the seedlings will fry!

FC.......There's no reason why you shouldn't start moving stuff out, if the temperature drops a few degrees just fetch anything delicate back inside until the temp rises again. I'll do that with my toms if necessary, but they should be okay under bubble wrap.

 

Hi Fc

I sit my trays and pots on polystyrene re -cyled from the tv , fridge , insulates and reflects the light and this sits on the staging , and water only in the morning so they are not soggy going into a cooler night then some fleece over the top.

With dahlias you dont want them to romp away yet so the greenhouse is better for them as well , other wise you it could be the middle of May before you plant out another 6 weeks .

During the day I also keep both windows open just a tad to aid circulation of fresh air this helps stop damping off etc

Spruce

 

The advantage I have of living here is, the temperatures tend to be higher overnight in spring and autumn than elsewhere. My plants have had no protection in the greenhouse this last week as the temperatures have been at 9c and above. Right now it's 11C!

 

Same problem here with the house resembling day of the triffids
Moved most of my stuff in to the un heated GH tonight now even the toms
Currently 11'c Outside
Bubble wrap and a large heat mat for back up

 

We are still in the process of rebuilding the conservatory, so I am "between conservatories" which is a bit of a bind at this time of the year. Conservatory needs very little heating, as attached to the house and sharing a wall with it. In the past I have put a small poly-tunnel in the conservatory, and a Metal Halide lamp in that with timer set to "nighttime" and that has provided enough waste heat to keep the tunnel at 10C Min.

About a week ago I put a [greenhouse] fan heater in the 12' x 10' and set the thermostat to 10C. Anything that can make do with lower temperatures is in the unheated greenhouse.

I don't think they are worth bothering with. An hour before dawn, if temperature is low, they will come on and all that residual heat will be pumping out and assisting the sun's rays long after the temperature has started to climb ...

Conversely, if the temperature plummets they probably won't give out heat fast enough ... nor into the far corners of the greenhouse.

A watt of electricity converted into heat is the same whatever the direct-heat type of heater, so for a greenhouse better IMHO to get a fast response one. The key is to keep the swing between on-temperature and off-temperature (hysteresis) to a minimum, and for that I think the most cost effectively solution is a greenhouse fan heater (cheapest one you can find will do) hooked up to an extremely accurate thermostat. The latter will set you back 50 quid, but should pay for itself in a season or two. Mine keeps the greenhouse to within 0.5C

I have a large fan heater: so I have a lot of warm air moving about, rather than a little very hot air. Dunno if that makes a difference. I bought it to shift cold air, in the winter, to reduce damp mould problems etc. at which it has excelled.