In article .com,
Connor T writes
Hi,

We've just gained a huge apple tree and were wondering how to tell what
it is.

It's well laden with fruit, from those we tried about a month ago we
assumed it was just a cooker of some sort as they were very sour,

That is quite early for an apple to be ripe. Only the earliest are ripe
in September. Most are not ripe until late Sep - Oct, and there are
plenty of varieties which are still not ripe when picked in November and
continue ripening in store before being eaten in Jan-Mar.

however now they've gone red and sweetened up a bit, and now edible (
altho not in my gf's opinion! ) Granny smith was suggested..

Do GS ever go red?

The
fruits are average sized, some quite large, but they're the exception -
this also something hinting it's not your average cooker??

Size is also to do with how healthy the tree is feeling. Good growing
conditions, lots of water leads to larger apples. Don't worry about
trying to improve the conditions - if the fruits are 'average size' the
apple is feeling pretty happy.

Also, it's going to get a big prune this winter, any recommendations as
to when, and how best to improve fruiting in coming years?

After leaf drop. Take out any diseased wood, any branches which are
rubbing across each other. Learn to recognise the difference between the
short knobbly fruiting spurs and the long new growth, and cut back the
latter severely to encourage more fruiting spurs.
--
Kay
"Do not insult the crocodile until you have crossed the river"