Leaving it bare would be more safe...I think the cement is a wonderful heat sink, without covering it up...

weebus,

the perimeter is not insulated, so will the concrete actually steal heat when the ground temp becomes very low, like January , for instance :-)

Scott

Yes, it will. You might investigate putting some polystyrene panels around the base of the greenhouse dug to a whatever depth your freeze goes to (plus some). You can often get PS boxes from supermarkets and greengroccers for free and cut them up with a knife for this purpose.

The boxes he is talking about are the kind shown on the bottom left and right of this picture.

:)

Here is a link that might be useful: {{gwi:309365}}

Well those and the 'broccolli boxes', which are completely enclosed with a lid, which I prefer - they use them for brassicas, celery and other things that like to be on ice.

You can also buy big panels fairly cheaply: here they sell 50x2400x1200mm for $50.

You know, I don't know about zone 6. We have them in zone 8 and the soil gets colder than the ambient air temp for such a short period of time that is really isn't relevant. In fact, I would say that the soil temps keep the concrete warmer, here.

buretachi,

You need to do the snow test.

If there are holes in the snow then heat is escaping. We just got another 6 inches, so in a couple of days I will take some pictures of heat escaping and post them here.

There is not much else to do from now until April except look for holes in the snow.