I should start by stating that I actually live in Madrid, Spain. The climate is more extreme than that in the UK with a very long and hot Summer, short Spring and Autumn and an often cold winter (sub-zero).

My father in-law has several seed grown hardy orange trees in pots (I think they're about one year old) and he wants to plant them out as soon as possible.

Would it be best to do this now (the weather is currently wet and mild) or wait until Spring?

Any advice would be much appreciated.