After producing all spring, asparagus benefits from a clean up and some fertility. First, weed the bed carefully using a knife and your hands. You want to cut the weeds out and gently remove them without disturbing the asparagus roots.
After weeding.
In order to not disturb the roots later in the season, it is important to prevent weeds from growing during the summer. I laid down cardboard along both sides of the row. This is a young asparagus patch, and still growing in a row. If yours is older, it is likely much wider than this or growing in a circle or oval. If that is the case, mulch the whole perimeter with cardboard.
I use Perennial Blend and compost from VT Compost Company. The Perennial Blend covers the cardboard, which will later break down, turning into soil along with the Perennial Blend. The compost is applied right to the crown of the asparagus and will feed the plant which will in turn feed the roots to make a great patch for next year.
The darker compost is in a strip right over the asparagus crowns. The lighter soil is the Perennial Blend. It hides the cardboard (which blocks out the weeds) and both will break down to feed the soil and the asparagus.