We recommend that you cut your lavender back around September time ( between 10:00am – 11:00am on September 15th!) once flowering has finished. If you have stoechas lavender (French, with the butterfly flower heads) cut back around half the green growth in March.
It isn’t just dead-heading your lavender. You want to prune past the flower stem, down to around half an inch above the hard wood.
This will encourage new growth in the Spring from the bottom of the plant.
The shape you have created makes a neat mound and gives structure over the winter months to your garden.
It is then ready for its new growth in the Spring, where you can give it a light trim just to maintain its mound shape.