It had grown quite weedy in the time between being built and when asparagus is ready to plant, which is now. To bulk up the bed I pulled out all the weeds and left them in the bottom and threw in heaps of blood and bone to help them break down faster then covered the lot with cardboard. Then I hosed down the cardboard and covered with a layer of straw and scattered more blood and bone and some chook manure pellets. This will all break down to create a nutrient rich base for the asparagus to grow. Over the top of this was five bags of potting mix and a few bags of composted manure.
These asparagus crowns are two years old so they shouldn't take too long to get established. I bought eight which should just be enough for our family of four. Weird looking things, they remind me of a Matrix Sentinel to be honest.

I read lots of different ways on planting them, but here's how I did it. Hollow out a circle roughly the diameter of the crowns in the soil. Make a little mound of well composted manure in the middle of the circle then place the crown on top. Spread out the tentacles all around the hollow then cover the entire thing in a mix of soil and manure. About two inches. Then gave them a good drink. You cover the ferns with more soil as they grow up through the soil.
You're not supposed to pick them the first year so as to get established. Then they should last for about 15 years if well looked after. Hopefully in about two years, come spring we'll be awash with delicious Mary Washington asparagus spears. But I think we'll call them Fat Bastard anyway. Fingers crossed they will be.