The important thing about an asparagus bed is that it's going to stay put for at least twenty-five years. All you're going to do from now on is top-dress and hand-weed. So get the drainage right and add goodness to the soil now. And - most important of all - get rid of all deep-rooted perennial weeds. You don't want to be trying to prise docks & thistles - or, even worse, comfrey - out of an established asparagus bed.
I double-dug my beds - proper double-digging, with the entire top spit removed & barrowed off and the spit below bastard-trenched - and added barrowloads of stable manure, plus sharp sand in the top spit as it was replaced. It was hard work, but that was about six years ago and all we have to do now is to pull out a few annual weeds by hand.
