yo,
all i did to my soil b4 planting was to dig out a bout 2ft down of soil and remove all the crappy clay soil, then into that hole i mixed in nice topsoil aload of compost and a few handfuls of sand then a handfull of ferts for good measures, they grew well.

i grew skunk#1 which has done really really well outdoors although now over the last few weeks due to so much rain there has been a bit of mold growing which sux ass, so try grow them in a green house.