You can take cuttings now if there are any non-flowering shoots. Otherwise late spring when all the shoots first grow is good. Nepetas can be such good flowerers that it's hard to find suitable shoots! You can also divide clumps in the spring once they are sturdy enough.

Thanks. Yes, I had to look hard to find any non-flowering shoots. I've taken off some side-shoots so will be interested to see if they root. Otherwise, I shall have to be patient and wait for spring. Another nepeta I bought this year is called Kit Kat; it makes small, dense clumps and is very floriferous - ideal for a front-of-border if you don't want anything floppy.