we planted 4 last fall. my father in law grew them from seed, so they are 3 years old now. he said he would pinch/clip the new growth fromteh trunk except for that onthe upper limbs. we did the same thing a couple weeks back. you prune it to basically define the shape of the tree, so use your own discretion. never prune more than about 30% of the tree mass as you could kill it. try to get things before they get too large, i get them when they are basically jsut green leaves forming on teh trunk.