hey man i feel for you :/

- I have heard on this page somewhere that some have been able to grow without for as little as 0 -1 c (but I've never heard of it in other pages where ppl grow out dore) i would say you can pull bud's out in temp's down to around low 60 f but if it goes lower then that. i would do something about it

- If I were you I'd probably end get insipid in a fan heater or just insulate your garage that's only one time you need to spend money on it and rockwool is not so expensive that it would give your the greatest loss of money.

In my opinion it would be worth it to just isolate your garage

--- Peace out ---