Thank you for contacting the UVM Master Gardener Helpline with your question. What a great opportunity to start your garden from scratch.

The depth of the soil will depend on the types of vegetables you want to grow. Some vegetables only need a few inches of soil while others such as some varieties of carrots could use 10 to 15” of soil depth.

I have a few articles that you will find helpful:

This article entitled “How to Use Compost in Gardens and Landscape” published by Oregon Extension recommends 8 to 12 inches of soil as described in this quote under How to Use Compost-Vegetable Gardens:

START QUOTE:

“For new vegetable beds, add 3–4 inches of compost. For existing vegetable beds, add one-quarter to 1 inch of compost per year.

After you spread the compost, follow these steps.

Add amendments such as lime and N-P-K fertilizer as indicated by a soil test.

Incorporate the materials into the top 8–12 inches with a digging fork, spade or rototiller.

Remove debris and chop the soil clods with a hoe, rake or the back of a shovel.

Spread the compost over the area to the desired depth. Wheelbarrows, 5-gallon buckets, shovels and rakes are useful tools for spreading compost (Figure 5).

Use a digging fork, spade,or shovel to mix in the compost and other amendments. Loosening the soil decreases compaction and increases the amount of air in the soil.”
END OF QUOTE

A few more references:

“Preparing a Vegetable Garden Site” published by the University of New Hampshire Extension: https://extension.unh.edu/resource/preparing-vegetable-garden-site gives recommendations on preparing your new site for the garden and what you can do this summer in preparation for your first garden season.

To protect your new soil this winter, you will want to put down a cover crop. This article located on the UVM Master Gardener Resources website addresses planting cover crops: https://www.uvm.edu/vtvegandberry/factsheets/covercrops.html

Once you have your soil in place, you can get your soil tested to apply any needed amendments making the soil optimal for the types of vegetables you want to raise. To learn more about requesting a soil test from the UVM lab go to: https://www.uvm.edu/extension/agricultural-and-environmental-testing-lab

If your property does not already have jumping worms also known as snake worms, you will want to try to get soil that does not have them. These worms live in the top 2 or 3 inches of the soil. With the amount of soil you are bringing in, it might not be a possible to find anyone willing to guarantee there are no worms. Sadly, all it takes is a single tiny egg. This article entitled “Invasive Jumping Worm Frequently Asked Questions” published by University of Massachusetts Extension: https://www.umass.edu/agriculture-food-environment/landscape/fact-sheets/invasive-jumping-worm-frequently-asked-questions. Personally, I find the most identifying feature is the way the worm moves. Jumping worms move like a snake with a side-to-side motion. Regular earth worms move in a straighter line.

Depending on the size of your new garden space, you could solarize the soil to kill any weed seeds and other pests, including jumping worms. This article on the UVM Master Gardener Resources page explains that process: https://www.uvm.edu/extension/news/invasion-jumping-worms

Finally, you might want to consider putting in raised beds. There are a few articles on the UVM Master Gardener Resources website that have information about setting up raised beds: https://www.uvm.edu/extension/mastergardener/gardening-resources

I hope this information is helpful. If you have any additional questions, please feel free to reach out. I hope you have good luck building your new garden space.