Answer: I'd fill the boxes with top soil. You can purchase it in bags at your local garden center or you can have 3 way topsoil delivered from a local agency. Either way, it should be ready for planting. Whether bagged or bought in bulk, topsoil is generally a mix of garden soil, organic matter and sand, all the right things for your new veggie garden.
As for planting, it is too late to grow the standard summertime vegetables such as tomatoes, peppers and squash, but you can certainly start a fall garden. Plant cool season veggies such as peas, beans, lettuces, broccoli, cabbage and carrots. Your local garden center may have seedlings but if not, you can plant seeds. After planting, I'd recommend covering the bare soil with a few inches of organic matter to help suppress weeds. This organic matter can be dug into the soil when the gardening season is over and it will further enrich your garden soil.
Hope this information is helpful!
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