I have two pyramid buxus semperviens trees in pots - have had them about 2 years but this winter one of them has gone yellow on the outside and the middle is brown. I noticed that it wasn't draining a couple of months ago so am worried I have drowned it! I made more holes so that isn't an issue now. I have trimmed it back and am hoping it will come back to life this summer but any tips on what I can do or is it a lost cause?