Keeping tender tree/shrub in pots over winter

Hello, I hope someone can guide me on how to keep a couple of plants over winter.

I have bought my mother in law an Albizia julibrissin and a Myrtus communis tarentina for Christmas. The original idea was to give them to her early to plant in the autumn (I bought them a while back), but she is having some landscaping done so has asked me to keep them till spring for her.

They are both currently in our annex which is unheated. It does get cold in there but not below freezing. Is this suitable? Also, do either of them need any water during this dormant period?

Many thanks in advance for any ideas.

I should think the Myrtus will be OK. I had one outside for years til a particularly bad winter wiped it out. I've never grown Albizia so can't help, sorry

I agree with nutcutlet that the myrtus ought to be fine.  As for the Albizia, the RHS site (link below) says it may need some winter protection so yes, an unheated annexe which doesn't get beow freezing should be fine as long as there's enough natural light.    As for watering, I'd keep them on the dryish side - they shouldn't need water as long as they're not actively growing.  On the other hand, don't let the soil get bone dry and dusty.  Just the dry side of moist - sorry, I can't be more precise than that but I know what I mean ..... 

http://apps.rhs.org.uk/plantselector/plant?plantid=5722 

Yes, plenty of natural light. The dry side of moist makes sense - thank you. I'll just give them a little if they start to feel dry.

Thanks for your replies and for the link.

if you don't water to much and I still put my pots on raised boards or feet even inside away from the glass if in conservatorie.

Thanks, flowering rose. Will do!