Batten down the hatches

Right, that's my greenhouse totally insulated with bubble wrap top to bottom. Bit of a fiddly job but well timed; it was only 5 degrees here last night.

I've also built what I'm calling a "hibernator". Big plastic tray with soil-warming cable in sand controlled by a thermostat. This is then surrounded by Kingspan foil-backed solid foam insulation sheets 2.5" thick and another underneath the whole thing. The front is lower than the back to allow a bit more light in than just through the top. A double thickness of bubble wrap attached to the top of the back which can be brought over the top and front like a lid.

In it are chilli plants that are cut back and ready to go dormant and small pelargonium cuttings that have taken root at the end of summer and are still small.

The greenhouse is 8' x 6' and I resckon that with the bubble wrap insulation, that 'hibernator' could keep the whole greenhouse just about frost-free during the depths of winter. If apck all the other plants around it I might get away with it.

Fingers crossed.

 

Hi JWK,

The soil cable is 100W. So if it was on all the time it would be like keeping a light on permanently. Not too bad cost-wise. However, the thermostat will turn it off sometimes so less electricity usage.

I won't be gowing anything new in the GH until early spring (very early spring) as it will be full of various things that I need to keep the frost off - various pelargoniums which will be cut back and kept dormant, a red banana in a bog pot, a ginger lilly and a big yucca. some agapanthus... to name but a few. That won't leave me much room.

That said, I have got some agapathus seeds from this year's pods and some phormium (again this year's seed) sown in trays with clear plastic lids to see if anything germinates - just an experiment really.

Cheers.

 

Damage I don't think a 100w heating cable is enough to keep your g/house frost free no matter how well it's insulated, you may need to consider a fan heater set low on frost guard setting to keep the chill off, the phormium seeds will need about 16c to germinate and the agapanthus about 18-20c may be worth investing in a propogator it will enable you to start stuff off earlier in spring.

 

I think you`ll be ok with 100w inside the box, the plants wont mind cool air if the roots are warmish.
You`ll just have to be careful about leaving the top uncovered for long periods or it`ll lose loads of heat to the greenhouse air and beyond.

 

I have a half greenhouse which I don't insulate. I only heat it if it goes below -2 degrees and I seem to get away with murder. It is quite sheltered in my cottage garden in Suffolk.

I germinate seedlings indoors on the windowsills during the winter.