I am glad you asked this question as I don't know I too grow box and mine have red tipped leaves.

I am no expert Codfather 1, but i planted my box about 6 years ago now.From tiny, 8 inch plants they are now 1foot thick by 1 foot tall. I trim them twice a year once they are smothered in new lime - green shoots. I never cut them back too hard. I only use tiny scissor shears as you get a much better and flat cut, once in may and once in sept - oct, if the summer has not been to dry. They are in neither wet nor dry earth, i do occasionally hose them down at the end of hot days with ordinary phostrogen. Thats it really.

Great, i maybe barking up the wrong tree, but could your box be suffering from a lack of a certain element in your soil? Hope this helps!!

My old mum says cut your box on Derby day !! Not sure why though. I trim mine as and when It needs it.

yes i would trim as grandmage sais i do with my cherry tree .like tiger sais you do it when it isnt the shape you cut it to.if your box isnt as big as you want it its worth putting a wire shape of what you want round it and cutting anything off outside this shape.this way it will grow quicker to what you want.

you may be right Tiger