Posted: 18/09/2015 at 10:20
My entire garden is former cow pasture that came right up to the back and side walls of the house. It was all very boggy but, after centuries of natural fertiliser it is very fertile loam over a clay subsoil. The front garden was tarmac poured over cobbles to make parking for tractors and so on.
We got a man with a bulldozer to dig us out a pond for drainage and then he scooped and levelled and smoothed and harrowed so we have a flat terrace, path and working area behind the house and gently rising land to our boundary. We made a large grass area and planted a row of shrubs for wind shelter and then, a bit later, widened that to make a deep border for perennials, a woodland corner and a damp bed next to the terrace where drainage is poorest.
The same man came back a while later to move the earth in the last part behind the house and make us a level veggie plot with railway sleepers as retaining walls. We then made raised beds for our fruit and veggies.
You can plant things on clay soil but you need to fork it over first to break it up and lay on loads of well rotted compost and manure - preferably in autumn so the worms and frosts can work together to break it up. Come spring, lay on another thick layer of manure or compost and plant in that. The same would apply if you do make raised beds.
Here are some interesting plants that will cope with poorly drained, clay soil - eupatorium, filipendula, lysimachia ephemerum, vinca minor, sympitum ibericum and dalmera peltata. Have a look also at astilbes, Japanese anemones, hostas, astilboides, primulas, especially the candelabra forms, ligularia and hemerocallis. If you like grasses, try molinia and hakonechloa.
You don't mention the aspect or exposure which will also affect your plant choices but, as it is the approach to your main entrance, I suggest a raised bed of some sort using local stone or solid railway sleepers that will last and look good when weathered. Either way, you do need to break up the pan of clay at the bottom or you'll always have drainage problems. I agree with Fidget about spraying persistent weeds with deep roots too - now and maybe again in spring if they re-emerge as these things can be very persistent.