prepping next years grapevines

If your ground is that bad, you may want to install land drains.
The actual trenches you describe sound similar to the ones I did this year.

its clay soil which has been worked and mixed (with manure) well over the years but it stiil forms a crust on the top if its too wet,cold,hot and the gullys i have around the edge of the plot (typical older style allotmenting to stop the grass from the path spreading into the plot ) have filled up with water in the past over a wet winter ,cheers

Hi Lebowski,

I have clay mixed with flint pebbles some the size of my fist. I started digging trenches but following rain they did indeed fill with water. The best advice I have found is to dig a hole about 12" square put chunky rubble in the bottom with well rotted compost on top. Plant the vines deep on sandy soil and shallow on clay (making sure to water if the ground gets dry). The main problem is the possibility of a hard pan where the ground has been continuallly worked at the same depth. In these circumstances a deep ploughing is recommended. As long as the roots can get through the clay layer the vines will be fine. I personally would not plant in winter. You won't gain much more growth than if you planted in spring and heavy frost can do a lot of damage to young roots close to the surface. Are you planting whites or relying on global warming and planting reds? I got my vines from Wine Growers Supplies. They are grafted and were £2.20 each. The only drawback is that the minimum order is 25. If you had some left over you can always give them to friends or make some.
Good luck

David