That’s why you need to prune twice a year!
To start off with right nowish! Between the end of March and the beginning of April you need to have finished the job…
If you have looked after your lavender properly you can cut it back to about 10-15cm off the ground. The flower heads will grow on this year’s new shoots. If you haven’t pruned your lavender regularly make sure not to cut it back too hard… as on the old shaggy looking wood you will not get any flowers. If it looks too sad for words… replace them and stick to these rules.
The second time you prune lavender is soon after it has finished flowering. In this faze (August-October) you can remove the dead flowers and then prune it back Lightly when flowering has come to a halt… I mean Lightly so the lavender has some strength to protect itself from frost in the winter months.
Happy Gardening, C