I leave my dahlias in the ground and mulch heavily over winter and have had good flowering success this summer, however, we are all informed to cut down the dahlias after the first frosts when the leaves and stems blacken. My concern is this - I live in mid Norfolk and our autumn and winters are very mild. We have had 2 frosts with no effect on my dahlias and chances are we may not get a heavy frost(s) this side of Christmas. if this is the case, when is the best time to cut them back if the leaves/stems don't blacken in readiness for winter mulching? Thanks for your help.