How commited are you to your plants, Somhairle? If you can be sure that you will lift the containers into the garage when the hardest weather happens and put them out again as soon as it is past, then they will probably be OK. The plants don't like to be without light but would be alright for a few days, no more. Last winter we had frosts down to -15 during November to January but the temperature did fluctuate up and down and we had days when it was only minus a little bit. With your proposals I would only have had the containers in the garage for several short spells and then back out again. Can you keep moving them in and out like this?

And is your garage actually warmer than outside? Because mine isn't - things in there freeze...

Yep, it would be. There is a large freezer in there that generates a fair amount of heat (well, I wouldn't want to live in it but, you know what I mean......)

Then Bulbaholic's queries are relevant ones - we all think we'll be dedicated enough to shift to and fro every couple of days, but often that dedication evaporates like frost on a sunny morning... But if you were dedicated enough, yes it would work well.

My garage is integral to the house and compost I bought froze solid last winter. If the soil is damp it will still freeze, though it should be a few degrees different to outside.

Just a thought, seeing there's not a window for light, I was wondering if you got one of those Daylight Bulb's and put it into a lamp then turned it on when it is daylight out side then turned it off when it started to get dark, even use a timer. Hope they survive. :o))

I could open the door each day (weather permitting) for a few hours?

My garage has an air brick and I put my Sollya heterophylla, Metrosideros and a few other tenders in there next to the air brick last winter which all came through unharmed. I'm lucky in as much as the rear door is glass. You must reduce watering to a bare minimum though.

Not sure opening the door would be sufficient, Somairle, in terms of light.

Even the main garage door? It allows a good amount of light in.

Thing is, if we have a mild spell of about 10 days, Somhairle (8-10 days is the usual pattern for fluctuating weather) it would be better to move them fully outside and then replace them if it got bitter again. In practice, if all you can do is open the garage door, then the plants will just have to take their chances.

I suppose so. I will need to play it by ear. If the forecast is reasonable - out they go. If it is poor - they stay in.