I have quite a few varieties of Thyme and that all go scruffy. Some die
back from the centre and just when you think they're dead, start to
green up again. They look particularly bad just after flowering - lots
of brown on top but trimming reveals bare twigs that take 6 months to
green up again.

The situation is full sun on dry, alkaline, sandy soil, no fertiliser.

Am I doing something wrong?

Steve Harris - Cheltenham - Real address steve AT netservs DOT com
A useful bit of gardening software at http://www.netservs.com/garden/