K wrote:
I didn't think the dying off was anything at all to do with frost, and
simply that lavender doesn't always shoot from 'brown' wood. With spring
pruning, I have seen both scenarios - lavender re-shooting, and lavender
dying.

Me too. The longest I've kept a plant is 8 years, a French one which
reach 1m10. And that I think was a miracle. I've experimented on my
allotment with them, and by neglecting them they have faired as well as
the ones at home, pruned in spring. However, the best show of lavender
hedges I've seen was at the Salford Sainsbury's in Manchester. I was
astonished by the longevity of these plants - hundreds kept on that
parking lot for well over 6 years, severely pruned in spring. Sadly,
they all died this year and still haven't been replaced (