If you ever decided to transplant/move mature asparagus plants, you may have a problem. I have a fairly large patch of asparagus, started from seeds that were germinated in my greenhouse in January, 2011. I only planted three of the seedlings in the garden in April. Those three seedlings became a 2x3' patch. I never harvested any of the spears, letting them all grow to give maximum energy to those expanding root systems.
This spring, I decided I wanted to elevate that patch of plants. I built up my raised garden last fall and boxed in the asparagus patch because the spears were all green and 5-6' tall. I didn't want to cover the asparagus with a foot of soil. Thus that patch was now lower than the rest of the garden. While the asparagus was still dormant, I dug a trench 1 ft. around the outer-most plants and a foot deep, thinking I would just slide the shovel beneath the roots and lift part of the "root ball" at a time, adding soil beneath it. I could NOT lift a single bit of that root ball. Those roots were so dense and so deep, all I did was end up cutting a bunch of roots. I soon gave up. My plan now is to slowly top that patch of asparagus with a mixture of dirt and composted leaves. It may take a year or two to get it raised to the level of my garden.
Since I did not direct-sow, I can't tell you about doing that. All my raised garden is a mix of top-soil and composted soil, about 50-50. When I planted the asparagus seedlings, I dug out three holes that would each be about 2 gal. in size and filled it in with potting soil, which I custom make. It consists of 1/2 milled sphagnum and 1/2 Black Kow. To every two gallons I add a cup of coarse perlite and a handful of Osmocote as well. I don't measure all this, just guesstimate. That's how my plants generally start. I guess over time, my garden will end up with a lot of perlite, since it doesn't break down. But that additional drainage will be a good thing (I think).
I have never seen a slug in or on my asparagus. Perhaps they are there, but I just don't see them and haven't seen any damage to the stems/leaves. Deer won't even eat it. I don't think that deer like all the "fluffy" stems-with-leaves. I broad-cast a couple of handfuls of Osmocote each April into the asparagus plants. Asparagus seems to do well with slightly moist soil and full sun. You want the bed to drain well.
