Kevin

Unless you hire some one with a stump grinder, digging out is on the
cards

What where the crystals you applied?

Bearing in mind that the Leylandii had grown well, it extracted some
of the nutrients value from the soil. My suggestion would be to
improve the soil. Try not to add something that has too much nitrogen
as the effect of this will be vegetatative growth. Whilst you mich
appreciate that for a large tree, if you are growing the apples as
bush trees, you will be doing a lot of pruning in the formative
years. Add something that will add body to the soil like home made
garden compost.

Clifford
Bawtry, Doncaster, South Yorkshire