Late spring to summer is a good time but to be honest i have taken cuttings at most times of the year with success.

I would wait until the new growth is more under way, and it is a bit warmer. I have some new small lavender plants and they are not growing at all yet.

Thank you very much for your replies

Take a cutting about 2.5 inches long, strip off the bottom leaves and put around the edges of pots of gritty, sandy compost. Make sure that you press the compost against the base of the cutting. A heated propagator would help too. They should start to root in about 4-6 weeks. Once they start to grow, pinch out the tops to get them to bush out or you'll have tall spindly plants. Pot on as needed.

Thank you very much Volunteer, very helpful.