First time apple grafter 
with a question about a less than ideal callusing temperature.
I just did some bench grafts today and I suspect I’ll have a pretty low success rate (more on that below) but I want to do what I can to get at least a couple to take.
I’m in the UK in zone 10a, so while we get some frost some years, we never get long freezing spells. Right now it’s around 7 to 10°C during the day and no lower than 5°C at night. Next week we’re going to get a couple days at 5 during the day and dropping to 2°C overnight. I’m not expecting it to go below that, but the wind chill here might just push it down to freezing.
I’ve loosely bundled the grafted whips together with the roots tucked into a small amount of loose, very slightly damp non-organic potting mix in a big plastic bag. I wrapped a few sheets of newspaper over the scions to block light but allow lots of airflow.
I can either stick them in the unheated north-facing shed at the end of the yard (super cold but no wind) or I can keep them in the coolest corner of the tiled kitchen floor, which is still around 21°C.
I know they’ll be alright in the cold in a week or two once the callusing starts, but is it worth keeping them indoors until that upcoming cold snap passes?
As for why I’m bound to fail 
circumstances meant I’m not set up for success. Scions are from mid October, kept nicely cool and damp in the back of the fridge the whole time, but the friend that gave them to me didn’t realise they need to be pencil thick - so some of these are just 2mm across and none are actually thick enough by any stretch. So the scionwood could be fresher, but also needs to be much older/thicker. Since they’re really rare varieties, and since I’d ordered rootstock before I knew the scions are probably useless, I just went ahead. What else can you do 
I grafted onto G214 (17 of these) and M116 (only 3 of these). Here are some pics of the mess!
