Posted: 22/01/2016 at 10:48
If its survived for 50 years it must have its roots in decent soil somewhere, otherwise it would be dead already!
If you wanted to give it a helping hand you could take out the fir trees. that would give the apple more light and water, then mulch the tree with some decent manure, make its about 3-4 inches deep (put cardboard or wet newspaper underneath it and it'll stop any weeds coming thru) and make it as wide as the branches reach out - but don't pile it around the trunk (they don't like it).
As for pruning it, you can hard prune but only take a max of 1/5 to 1/4 of the branches away, start with anything dead, diseased or rubbing and with a 50 year old tree you might find just taking them out will be the 1/4 of the tree.