First, there's something called June drop - as you might expect, happens in June, and the tree naturally lets some fruit drop, so that explains some of the ones on the ground. Secondly, its been a dry year, so the fruits left behind may not have had enough water to swell properly, or they needed thinning out so that each fruit could develop properly without being crowded by other apples either side or around it.

We inherited apple trees when we bought this house eighteen years ago, as they were already in the garden, we don't know how long they'd been there.

The two main ones are cooking apples - last year we harvested over 200 lb in weight of apples off them!!! (they're about 20' high, and produce very large apples with a 'blush' on one side). There is a 'June drop' when the trees drop all the rejects, they're normally tiny, marble sized apples, which wouldn't have developed into apples. What we do, when the trees are in blossom, is snip off any spurs (at the ends of the branches beyond the blossom) which don't have blossom. The amount of apples produced depends on the blossom. Basically, no blossom no apples.

The other two trees are eating apples (Granny Smiths) and these are much smaller, and to be honest, still taste bitter, but we don't get very many of these (they're about 30' high and need 'topping').

Hope this is of some help to you.