Answer:
Though not a plant I have leaves. though not a beast I have spine. Though many wouldn't need me I am more valuable than wine.
I know a word of letters three. Add two and fewer there will be. What is the word?
I contain six letters minus one and you got twelve.
I go through a door but never go in, and never come out. What am I?
It flies around all day but never goes anywhere? What is it?
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.