It really needs to be done in the hottest months (or hotter parts of spring/fall) throw a giant piece of black plastic over it, weigh it down tightly with bricks and let it cook. If the bed is a bit deep, you can dig out half the soil, lay it beside the bed and cover and cook out that stuff, then cook out inner bed too.

What do you think the problem is?

celeste, don't know yet why you think you need to do this, but suggest you research soil sterilization before you act. This will kill all the bad things, but also all the beneficials in the soil also.

Consider posting on the Soils Forum or search this subject there.

Rosie