Leaf by Stephen Michael King

From chapters.ca:
A green tale for all ages. An enduring friendship sprouts between boy and plant. When a little boy runs in a panic from a haircut, a bird sees to it that his luxuriously follicated head is put to good use and drops a single seed right on top. Time passes, and wait... could it be? Something grows. A leaf! Instead of trying to rid himself of his new living hairstyle, the boy learns how to make the leaf grow, and, in turn, winds up growing a lot himself.