Let it flower.

Having a lavender hedge, I have discovered that there are two theories on pruning lavender, and proponents of each often deny the other could possibly work.

Theory 1 is that you should prune in late summer after flowering. In this theory, you should only prune in the green area, if you prune a stem down to bare wood it will probably die in the winter. This is what lavender farmers do.

Theory 2 is that you should prune in spring, but late enough that there won't be a serious frost to get into the cut wood. In this case you can (if necessary, eg to rejuvenate a leggy plant) prune back into the old wood, and it will shoot out from the old wood, though you will probably lose a few branches, and you should expect fewer flowers after a hard pruning.

I think the proponents of Theory 1 worry about frost getting into the wood and if you are harvesting the flowers you won't be so worried about appearance from Aug-March. But I like to leave the dry flowers on through the winter. It also depends on variety. I wouldn't prune French Lavender as hard as I would dare with normal lavender.