The youtube video of the construction suggested a unique way to fill the space. He collected downed tree limbs and sticks, which we have an almost unlimited supply of. He then puts leaves, then finishes with top soil. What I will do is after the limbs and sticks, I will add a bunch of cardboard I am collecting. Then we will go down to the evil old cow pond and bring up buckets of good ole Virginia clay, then add the 2023/24 compost, then finish with the top soil that was on the 2023 garden. I like the wood idea, as it not only helps with volume, but it keep the beds from having huge amounts of soil pressure pushing out the middle and bottom portion of the bed for at least a couple years. Am also stoked on the wood breaking down over the next 3-4 years and the bio-nutrients that that will add to the garden! Should get away with almost a $0 fill fee, just the cost of diesel to get soil up!
I am hoping 10-12 inches of great top soil for the 1st 2-3 years will be enough for any roots of vegetables we grow, but that is a guess!
Do you fill it with dirt or are the bottom layers stone or pea gravel?