Surprisingly Clay soil is very good for most vegetables and flower plants from a nutrition point of view. Problem is drainage. Wet in Winter, Dry in Summer. It is better to have clay than sandy soil. My garden is very heavy, brick pit clay in parts. Really I can make decent bricks with it !!

The PH is unknown, but is generally neutral'ish.

MOST plants will survive and thrive in a clay soil. Vegetables, flowers and shrubs.

Be careful with planting too early because clay takes longer to warm up, but is good once it is warm. Loads of grit,sand and humous helps, so is never using a spade, just a fork. There is a very good article from "Anglian Gardener" http://www.angliangardener.co.uk/green_up_your_fingers/clay_soil.htm about clay soil.

If planting shrubs or large rooted established plants, just make the hole 3 times bigger than needed and dig in a load of compost/grit to stop the hole becoming a water sump and has drainage.

Shrubs: Cornus, Magnolia, Salix, Weigela. Perennials:Aconitum, Helenium, Hemerocallis, lysimachia, Lythrum, Persicaria bistortum, Polemonium, Rudbeckia, Solidago. Ferns: Matteuccia, Osmunda, Woodwardia. Other things may well survive quite happily in it too, you need to experiment a bit, perhaps.