You need to lighten up that heavy clay soil first before you put the asparagus in, they don't like being waterlogged - I dug sand into mine as well as well rotted compost etc. Plant on ridges, not too deeply. About 2 ft apart though opinions differ. I do mine in a bed, maybe others do single rows, I see them ususally in beds. If you put them in now, keep them watered if its dry weather.