[cc]

Instead of starting a new thread I might as well ask here.
Going to plant trees on a hill,  soil is limestone/chalk in clay. How is it best to go about it? Not easy to dig could use a hole borer? How deep and should I put compost or topsoil in the hole? How deep should I dig down? Thank you

[mumofstig]

Probably better to start a new thread when the old one was from 2008 

[steved]

For fruit trees you cant bury deeper than the graft site, this should be about 6" above soil level. You can of course dig a bigger hole and fill with as much organic soil improver as possible and plant into this. Clay soil, although can be a PITA, is quite nutrient rich and as its going to be on a hill, shouldnt result in the roots sitting in standing water-which fruit trees really dont like.
I did similar, planting a mini orchard at the back of my allotment that I cleared, this was very clay so I was advised to grow trees on a more vigorous rootstock due to conditions being less than ideal(MM106)

[New shoot]

I was advised to grow trees on a more vigorous rootstock due to conditions being less than ideal(MM106)

That's good advice.  It also works well for trees you want to train as espaliers and other shapes, as they grow fast and give you lots of wood to work with.  You can always control the top with pruning, but a beefier rootstock really helps trees in poor soil.

The clay/chalk combo is a bit tricky.  You can end up with water draining into a planting hole like a sump and drowning the tree.  Dig as big a hole as you can.  Dig tree and shrub compost, or rotted manure or home made compost into the soil you take out and plant with that.   You want bulky organic matter in there as it does 2 jobs.  It holds water in the soil, but it also breaks up the clay to let it drain.