I don't know. In my old garden, I only had about a 6-8" depth due to hardware cloth installed for gophers. They did fine. Nancy

I have read that asparagus roots can grow a few feet into the ground. Perhaps the idea is to anchor the plant better. Like Nancy, I am growing asparagus planting only about 6-8" deep. They are thriving but too early to tell about harvest just jet. It will be a couple of years for me.

shp I think I started my gus bed about ????? 15 years ago? They did great except for some drought years. They bounced back with a few losses after a couple of wet years.

I really miss my gus and don't have much room to plant again where I now live.

I think it's probably a frozen ground issue in much of the US.