Amurs are really hardy and you can trim them anytime ..I know most say wait til late summer or fall to keep the sap in check but I have trimmed these year round with no problems ...and I mean i have severely trimed them!!!! they grow like weed really fast and outgrow just about any place you put them... I set a big brush fire too close to one and lost a bunch of brancheds last spring .... it came back and by fall was three times it's "burnt" size I love 'em BTW but if left single trunk they can get 20 ft tall in probably 5 years around here ...SO have "at it" is my opinion I really don't think you could harm it if you tried!!! BTW don't do this with JM's!!!!! David