Prior to this, we had direct planted into the ground. This resulted in so many problems, mainly because our soil goes to heavy clay about a foot down. Our beds are 8 inches raised, plus the 10 to 12 inches of modified existing soil has created a reliable profile for the next couple of years. I went further and got a container of fishing worms for each bed and scattered them on the top one evening to let them work in. Hopefully these efforts pay off.