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I'm still working on sifting through an area of my backyard in order to make a garden for next year.

I'm pretty sure it used to be a gravel lot, since all the rocks are the ones found in gravel roads, and I've found various building materials like bricks and crowbars.

I would like to plant root vegetables like radishes and carrots, so I'd like to be sure that I have the soil fixed deep enough for those.

How deep do I need to go in order to have a healthy garden?

  • What kind of garden are you planning on? – J. Musser Oct 20 '14 at 2:17
  • @J.Musser Vegetable mostly. Carrots, radishes, peas, cucumbers, and watermelons. – The Flash Oct 20 '14 at 2:43
  • Why not do raised beds and save yourself a bunch of digging? – nportelli Mar 4 '15 at 14:30
  • @nportelli Too expensive considering I'm probably going to be moving in a year or two. And I don't mind the digging, I find it relaxing and it's good exercise. – The Flash Mar 4 '15 at 14:35
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Although much root activity occupies the top 6 inches of soil, many vegetables need 2 feet of soil or more.

Janet Beal

The depth of your bed will be determined by what you want to grow.

  • Shallow roots - 12-18" - Leafy greens, broccoli, cabbage, raddish
  • Medium roots - 18-24" - beans, cantaloupe, cucumbers, summer squash and carrots.
  • Deep roots - 24-36" - pumpkins, winter squash, watermelons, sweet potatoes, tomatoes, asparagus, and rhubarb

I recommend a double dug bed. Which means, digging down one shovel length, setting the soil aside, and then digging down one more shovel length. The length of a spade shovel is roughly between 8 and 12 inches, so this results in a 16-24" depth. Never have I actually dug down 3 feet for a garden. 2 feet is plenty.

It sounds like that is going to be a ton of work though. (I know, I've tilled up land just like you describe by hand. I ended up with a pile of bricks chest high and several feet in diameter.) So, with that in mind, you may want to dig down just one shovel length (12") and build a raised bed on top of that. It's a little more pricey to go that route, but you'll save yourself hours upon hours of labor.

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    Good answer. I'd just like to add that while many plants root this deep, the majority (often over 90%) of the root systems are in the top 4-6 inches of soil. – J. Musser Oct 22 '14 at 19:26
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If you will only be planting carrots in the spot, then you would remove rocks down to the level where the root would grow. Removing rocks further down would not be of any benefit to the carrots. If you plan to clear a large area all at once, and you will be planting things that require removal of rocks down to, say, two feet, then you will be screening the soil based on the requirements of your most affected crop such as the carrots.

If the ground originally sloped, then it is possible that the previous owner filled the lower parts of the lot with construction debris such as concrete blocks and siding. If so, you may find that you have quite a lot of material to remove.

Another option would be to create raised beds for your carrots on top of the existing soil.

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    Might well be easier to say "here is a well-drained base" and then build the garden up from there. A LARGE truckload of soil can be remarkably affordable .vs. all that sifting. You could haul in a bunch of horse manure or other compost materials, spread that, get soil, spread that (or place it in beds leaving the paths nearer gravel base level) and never look down - just add more material on the top as time goes by. – Ecnerwal Oct 20 '14 at 1:07
  • @Ecnerwal At $26/yard, screened topsoil might not be something everyone can afford. – J. Musser Oct 22 '14 at 23:06
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    ..yet it will probably come out well below time valued at $10 hour, especially when sifting "rock from gravelly material" that needs additional organic matter, etc. to become soil. Sweat equity ain't cheap. – Ecnerwal Oct 23 '14 at 2:01

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