If you read gardening books, or watch much of the TV gardening shows you will be advised to prune your lavender in the spring. The dead flower heads can offer a little bit of frost protection and some people like to see them on the bushes through the winter.
I don't do this! I always trim back lavender, especially English Lavender in the late summer or early autumn as the flowers die. I'm not a great fan of dead lavender flowers, and I am convinced that trimming them back now helps keep the bush tight and tidy. Leaving the pruning later can allow them to become a bit woody and leggy. Trad
itionally commercial lavender bushes would have been replaced every five or six years but with my system they stay tidy for a lot longer.
If you like you can also separate the dried flowers and use the in potpourri, or sow into muslin bags for your great aunt or indeed your own knicker draw!