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Old August 14th, 2009, 02:08 PM
Andrea J Andrea J is offline
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preventing leaching into sandy/stony soil

Hi, I moved to an area with extremely stony/sandy soil - basically river rock with a bit of sand/gravel in between. I plan on building a bunch of raised beds for a veggie garden. My neighbour also has raised beds on similar soil, and she found that the nutrients in her soil quickly leached out. Good topsoil mixed with compost and manure was very sandy just by the end of one growing season. The only thing she had at the bottom of her raised beds was landscape fabric - not enough.

My question is: what can I put at the bottom of my beds to prevent this kind of nutrient leaching? I want to allow drainage and place for worms to come up into beds, right? Ie, just putting plastic or wood at the bottom of my beds not such a good idea? Would a layer of newspaper or straw at the bottom be enough? Ideas?

Thanks!
Andrea
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Old August 14th, 2009, 07:21 PM
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growing4it growing4it is offline
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Re: preventing leaching into sandy/stony soil

Nutrients leach out of soil by moving with water. If the subsoil is very permeable and water moves easily, the nutrients, I would expect move easily. Besides, all soils needs to be replenished with organic materials to replace lost nutrients - nutrients lost due to leaching and to uptake by plants.

If your neighbour experience inadequate containment with landscape fabric, solid wood boards would probably help. Could you also 'seal' the bottom of the raised beds with a clay-type material? Something durable but would still drain.
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Old August 15th, 2009, 12:40 PM
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cowboy cowboy is offline
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Re: preventing leaching into sandy/stony soil

A layer of clay on the bottom is the best solution. People who have lawns on similar rocky ground will first put down a layer of clay before adding soil and sod. Soil with high amounts of organic matter or adding zeolite will improve the soil's nutrient and moisture holding capacity.

Good luck.
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Old August 18th, 2009, 10:02 AM
Andrea J Andrea J is offline
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Re: preventing leaching into sandy/stony soil

Thanks for your replies! And I did meet another neighbour who did the clay thing for his lawn and garden. That was about 20 years ago, and things are still good. Where does a person get clay??!!
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Old August 18th, 2009, 01:57 PM
Ron B Ron B is offline
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Re: preventing leaching into sandy/stony soil

Buy a more retentive soil and dump that on top of the too sandy stuff, plant in that - without mixing the two together.
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Old August 19th, 2009, 10:46 AM
Andrea J Andrea J is offline
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Re: preventing leaching into sandy/stony soil

Hi Ron,
Yes I will be putting a more retentive better soil into the raised beds, the problem is that because the ground underneath the raised beds is so porous that (for my neighbour anyway), the nutrients and good stuff in the top layer of soil just gets drained right away, leaving only the sand in there because the water just flows right through. Her good mixture of compost, topsoil, peat moss, etc was left as a sandy soil just at the end of one growing season. I think I'll try the layer of clay underneath the good soil in the raised beds, that way the water won't drain as quickly but there is still allowance for some drainage.
Thanks!
Andrea
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Old August 19th, 2009, 06:41 PM
Ron B Ron B is offline
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Re: preventing leaching into sandy/stony soil

I'm talking about putting a less sandy soil on top. This is not the same as amending a sandy soil, where amendments decompose more rapidly than in a finer-textured soil.

Scooping out the existing soil, setting it aside, locating a clay soil, laboriously digging it out and re-locating it to your site, then putting the other soil back over the top sounds like way too much of a bother to me. And I have serious doubts about doing anything to impede the drainage of a vegetable plot. Clay has even been used to create naturalistic ponds before, such as in the native garden at UBC.

The problem there is the texture of the topsoil, not the subsoil. Plants even grow on top of boulders in nature if a suitable layer of soil has formed over the top.
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