Im planning on repotting my 2 large trees as i bring them into the house for the winter, ive got the pots ordered , at the minute there in 160 Litre pots and im going to 200 or 230 litre pots as the next size up that are stocked

the trees are now quite large , but i wouldnt mind them growing a bit bigger so i dont need to keep the pots small to restrict the roots at all

at the minute there potted in

12 foot lemon tree , 9 inch diamiter trunk, in 160L pot

9 foot mandarin,7 inch diamiter trunk, in 150L pot

In the middle of the summer i chopped away some drain holes in the pot of the lemon tree and found while the roots in the pot are fine, they all hit the outside edge of the pot and make a thin layer all over between the pot and the compost, they look to be quite crumbly and dead were they touch the pot, removing the outer edges would give a good root system

Do i chop them all off leaving a nice rootball to surround in more citrus compost , or should i leave them all matted on the outside of the rootball and just repot like it is?

A book i have here says that in italy the old trees are kept in the same size pot by chopping the outer 6cm layer off the roots and repotting , is it safe to do this without killing it! ( only a thin layer were it touches the pot) even though im increasing the pot size a bit, i will be leaving most of the compost on it and adding new on the outside as much as possible, brushing into the outer parts of the root system a bit but not removing all compost?

Will repotting and crumbling the outer layer of roots make any difference to the growth of the fruit on the tree now? (dont want it to fall off!)