What did you get? The last time I got mulch from the county it was full of things I didn't want. I'm in Nebraska. I hate the idea of buying dirt, too. Of course I say rabbit poop on sale on ebay so everything has value!

I went ahead and got the compost from our local waste management. That was on the suggestion of several local Master Gardeners. So far it has worked out VERY well. the plants are going well and there hasn't been much weed pressure from the compost. It does drain pretty quickly so I have had to keep up with watering. Otherwise it has been a great option.

Hi Philip. I was in a similar situation but filled my new beds with pre-mixed garden soil from nursery (a blend of compost, manure and top soil). The plants are not growing so far. I'm in Ontario (zone 5b) and we had a terrible rainy month with many downpours. I'm afraid that could be part of the problem. Did you just fill your beds with compost only? No soil at all? Did you put any cardboard or landscaping fabric at the bottom of your beds? Thanks

I used to get black dirt by the yard when I was doing perennial nursery back some decades ago. That was just fine, but it paid to get it sterilized or it brought in all kinds of hitchhikers; some of which I still have not managed to completely irradicate. I had to learn the hard way.

If you are just going to raise the beds above the ground by the height of the boards, check out local black dirt or topsoil suppliers in your area. A small order, if you have a pickup truck to save on delivery charges, will hardly cost you as much as the lumber you will use to side the bed. Looks to me like you will need a bit over a cubic yard 36-48 cubic feet. FWIW you can probably rent the pickup truck for something like $20 and be able to bypass any higher delivery charges.