When we got out here, we'd brought our five existing galvanized stock tank raised beds and then decided to add three more to the collection to finish out the veggie garden in our expanded back yard. And with that came the task of filling them. Eight 6'x2'x2' beds. Dang...
So with that, we decided to go Full Hügelkultur to fill these babies up. And thanks to the considerable number of plants around the property that did not suit our style at all, we had just what we needed. An old yew that had to come down, far too many other evergreen shrubs (very staid, 'parking lot' plants as a contractor described them), not to mention some arbor vitae that we could not stand? Plus a bunch of scrap logs that left behind by the seller? BAM! They were all used to fill the beds just over halfway, ensuring less potting soil was required (saving tons of $$) while also improving the drainage in the bed (something we found made a HUGE difference when we experimented with this in couple of the beds last year) while the mounds of scrap branches slowly degrade.
Next, I covered the scrap greenery with reclaimed burlap coffee bags from the local roastery to keep the drainage going along with the holes drilled in the base as well as setting them atop a bunch of broken bricks left on the property. Then I poured on 3-4 bags of organic potting soil (buy once, cry once) and, for winter prep, just covered them with old cardboard boxes to keep the critters out til it's time to plant.