All I can add is, don't underestimate the distance the roots spread out over the years. I was cleaning grass out from a path next to them, last year, and kept coming across asparagus roots. I moved the path sideways a little more so that I would not be treading on them.
I have grown asparagus for about 40 years, and in my current allotment I put in 20 crowns of all male Dutch hybrids (one is Gijnlim, I forget the other, another "lim" one) four or five years ago, and am very pleased with them. I have never put salt on them, but in a previous life the asparagus beds got heaps of well rotted pig manure every autumn.
I never water them because I assume the water would have to be torrential to reach the roots, and my allotment has none. I admit that they were not so prolific as usual last year, but usually there are more than we can eat and give away, without watering.