Possible Clues:

• Hitchin caller regularly observed hard water in winter
• Spear-like shape formed by the freezing of dripping water
• It comes to a point when it's too cold outside
• Bit of Christmas tree trimming
• One hangs on a house
• Something hanging near Christmas lights, maybe
• Wintertime dripper
• Glacial cave formation
• Dripping water frozen
• It spikes in winter?