Posted: 23/04/2013 at 09:45
Pieris will only work if the soil is acidic, and it really prefers good well drained soil to thrive, so I suspect it will struggle on your clay even if it is acidic, unless you prepare the planting hole well. I have similar soil to you, and lost quite a few shrubs / trees by just digging holes big enough for the rootball with a bit to spare. They died because of lack of moisture in dry summers and sitting in saturated soil in winter.
If planting a shrub or tree I now use a pickaxe, 5 ft long crowbar and mattock to break up the underlying hardpan down to at least 2 feet deep and at least the same across. Sometimes I wish I had a pneumatic drill!
Thee are a few shrubs that can handle heavy clay well with out a lot of preparation. One is the cornus (alba, flaviramea, sanguinea, Midwinter Fire etc. )