I've got a herb patch on my allotment among which I've got some
curly leaf parsley. Up until a month or so ago it was growing beautifully,
with lots a bushy green leaves which were quite regularly picked off,
but still with plenty left on. But recently the plant has turned yellow
and looking worse for wear. All the other herbs in the patch (esp. the
flat leaf parsley) look fine. Any ideas of the cause?