The first thing to do is remove the old asparagus stalks. This can be done using hand secateurs but I find it simpler and quicker to remove them with a brush cutter.
 
I cut the stalks off at the ground. Some gardening books recommend that you cut the stalks off at seven to ten centimetre above the ground but I prefer to cut them off at the ground, it doesn’t seem to effect the yield but it does make it easier to add manure and mulch to the bed. The stalks are quite soft so they can be chopped up and composted.
 
Lightly hoe the bed to break up the soil. You should not dig deeper than three or four centimetres, any deeper and you run the risk of disturbing the crowns. Apply manure. The general rule of thumb for a standard vegetable bed is about a shovel full per square metre but when it comes to asparagus I double that amount as asparagus can handle a richer concentrate.
 
I prefer to use cow or sheep manure as it contains fewer weed seeds than horse manure but go with whatever is the cheapest and easiest to obtain. I also add a small amount of dynamic lifter or well crumbled dry chicken manure, some blood and bone and some rock dust (for essential minerals).
 
Mulch can be added now or after you have finished harvesting the asparagus in late spring. Both have their advantages and disadvantages.
Mulch is an effective insulator so soil underneath mulch is always cooler than bare soil. Adding mulch in July means that the start of the asparagus season will be slightly later (only a few days) as it is the soil temperature that triggers the asparagus growth. But leaving the mulching until after the harvest means that weeds will find an easy foothold in the bare soil as the days warm up, plus when you finally add the mulch you will have to spread it around the growing asparagus.
 
Asparagus stalks are notoriously brittle, they can be easily broken as you work amongst them applying the mulch. For this reason I prefer to mulch the bed in July.

It also gets the job of preparing the asparagus bed out of the way in one hit.