Fruit How Can I Rehabilitate A Fruit Tree (to Make The Fruit Good Again)?

How can I rehabilitate a fruit tree (to make the fruit good again)? - fruit

I moved into a house with a beautiful peach, plum and pear trees on the lot. Probably my first review, the fruits are cranky and do not eat anything good in this season. You are on the small side and is likely to sour.

What can I do now to remedy such fruit trees so that eventually (the next season or several seasons from now if necessary) start again too big and good enough to eat? Is there a special fertilizer for fruit trees is usually available? Any other tricks to learn?

No idea how long (how many stations), could be taken by the redevelopment of a "wild fruit trees?

Thank you!