Posted: 05/01/2014 at 08:34
Is it pot-bound? If so personally speaking I'd go up one size bigger pot and repot in JI No 3 as above.
You can tease out the roots a bit to loosen old compost before potting on with fresh compost - the more fresh compost you use the more nutrients you'll be providing for the tree - it's a tricky line you have to tread - providing enough nutrients to keep the tree healthy without it growing too much.
No tree will remain the same size - even bonsai trees grow, but they can be pruned to keep them small - Christmas trees do not take kindly to pruning - it spoils the shape.
I'd let it grow slowly, and then, when it's too big for you to use at Christmas I'd bite the bullet - shred it and start again .............. heartless I know but the other option is to give it its freedom, plant it in the garden, and allow it to become one of the many huge lonely ex Christmas trees at the bottom of gardens, pining* for a forest
*there's a joke in there