United Kingdom 
I have had two large holly trees in large barrels for around six years, they have always been healthy and dark green but are now getting pale and a little yellowish and one is getting quite sparse. Any help would be appreciated. Thank you.
15 Jun, 2015
After six years, its likely the plants now need to be transferred to the ground because they've run out of root room. You haven't said which variety of holly they are, but even the smallest makes 10/15 feet eventually, so its inevitable that, contained in pots, they will grow out of their containers I'm afraid.
15 Jun, 2015