Answer:
What grows in winter, dies in summer, and grows roots upward?
I open wide and tight I shut, Sharp am I and paper-cut fingers too, so do take care, I'm good and bad, so best beware.
Left to right I’m quite bright. Right to left I might bite.
The more of it there is, the less you see.
My first half is normally made of stone, my second is crazy, and I taste sweet when complete.
I am rarely touched but often held. If you are smart you'll use me well. What am I?