salt petre and apple trees

Know of no reason why you should. Might add a bit of growmore or similar (slow release fertiliser) to the soil that you put back in but other then that they should be fine.
Then a good watering when they go in.

Ok thxs i did not add any.

As for the tree's two of them have about 12/15 apples on them, these are the mm106 root, should i pull the fruit off so the tree can get a stronger root, i might be wrong but im sure i read it is the best thing to do, or was that after year one, these tree's are two year old and just planted today.

You remove fruit the first year after planting, but i always leave one on just for a taste

Thxs ill crop them tomorrow, all but one each tree

Saltpeter is widly used to spray some fruit trees to increase fruit held on the tree, the high levels of pottasiuma and nitrogen help the plants,

it is often used on citrus plants for this reason and to add nitrogen rapidly if theres a defficency , applied through the leaves or roots instead of using urea that can cause problems due to high levels of biurette in some urea causing fertiliser burn

I cant see a normal amount hurting a tree any more than any other fertiliser, i often water things with it in a mix with other components or individualy