Greenhouse Heating

This is a native of eastern Australia, from south of Sydney up to just south of the tropic of capricorn. I know this because I was looking at one myself. So although they may experience frost occasionally in their native habitat, I doubt that it would be the norm. Is the pot and the medium frozen - if so I fear it may be done for......
It's a shame, as the mature bush is rather lovely.

Your heater is keeping the air in the greenhouse at 10 to 20C, Steve, but the ground will be conducting cold from the outside into the floor of the greenhouse and the pot will have frozen from the bottom up. I wouldn't put it too near to the heater but definitely raise it up off the floor so that the warm air can circulate round it.
I know nothing about hibiscus but wouldn't throw it out yet - give it a chance.

That’s what I thought bulbaholic the other thing that I am going to do is line the floor with some heavy duty polythene when this bad cold spell is here it was -13.5 last night on our deck that’s the coldest that I have ever seen it here. Fortunately meanie I have a another plant that is doing brilliant and a few seeds so all is not lost

I agree - don't throw it out yet.
Simple staging with insulating properties? Put pallets on the floor, fill the space with that polystyrene packing "stuff" and cover with offcuts of carpets. If you want a single piece and cheap alternative to several offcuts, marquee hire companies use a "disposable" carpet at certain events - it's probably only used a couple of times before being thrown away. Also makes very good weed suppressant material.

I totally agree with Meanie & Bulb, the secret is keeping the heat in and circulating, I know this sounds obvious, the heat rises and a layer of bubble wrap throughout the greenhouse does wonders and it is relatively cheap. I have plants in mine now and they are all 3-4' off the surface. Take a look at my pictures.

bubblewrap lasts for years - as does polystyrene. We line our greenhouse with bubblewrap (must change it this winter - 10 years is too long!) and use slabs of polystyrene on floor and shelving to insulate plants. All the polystyrene packaging i get (every parcel seems to have it) gets broken up in the bottom of large tubs - to improve drainage (instead of crocks) and keep the weight down (the husband moans about moving them around else!) Toilet rolls are good for sowing sweet peas in.... what else can we recycle in the garden???

Hi All
The greenhouse was lined with bubble wrap a few weeks ago so today I have resurrected some old staging from an old plastic walk in greenhouse and the pots are now about 4/6 inch from the ground I borrowed my dads probe and the gravel was below freezing so it looks like the ground is conducting the cold from outside so hopefully problem is solved
Thanks
Steve

Hoya, what a good idea re the polystuff, i'm going to try that. Thankyou.