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After our house was built there is quite a bit of hardfill (river pebbles) mixed up with the topsoil around the section (approx 180sq.m.). We want to level the section, and loosen the top layer of soil to ready it for laying a lawn and growing a garden, and we're wondering what to do about the pebbles.

We understand that leaving too many stones in the soil will reduce the capacity of the soil to hold moisture and can also prevent tree roots from forming normally so we're considering sieving the soil somehow. It sounds like the local landscaping contractors can't help us with sieving, so I suppose it will have to be done manually.

We'd be happy if we could remove any stones with a diameter of 20mm or more.

Ideas so far include:

  • bird-netting (dump the soil on top, then lift the netting); this might be hard work when it comes to breaking up clumps of soil?
  • a wooden frame (supported, somehow) covered with chicken wire (several layers of wire to reduce the gap size); this might get stones stuck between layers of wire
  • something more rigid from the local building recycling firm (have yet to see what they've got)

I would really appreciate any other ideas, or accounts of what's been tried and has proven effective. Thanks!

[Edit] Have added a photo to give an idea of what we're dealing with. This soil was dug up and scattered around the left side of this photo by contractors putting in the fence post to the left. stony ground, with brick for reference

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4th option: consider xeriscaping and just get more stones. ;) –  DA. Nov 23 '11 at 19:38

2 Answers 2

up vote 10 down vote accepted

The wooden frame you describe is what I use, but instead of chicken wire I use hardware cloth (wire mesh). I have one frame with 1/4" mesh and one slightly larger (3/8"? -- I think 1/2" would be too big)). My large frame measures about 3' square, the small frame is built to fit over a specific bucket and measures about 15" square.

The biggest problem with frames like mine is that you have to physically shake them by hand to get the soil to shake out. If I was going to build another one (and I likely will), I'd make it maybe 2' wide by 4-5' high so that I could set one end on a sawhorse and toss material onto it with a shovel. The material (rocky soil, compost, etc) would "roll" down the face of the screen, the fine material would fall through and the large material would stay on the front.

If you didn't want to build a frame, I've seen people just throw a section of hardware cloth over a wheelbarrow and toss material onto it. Looks like more ongoing work though -- I think you're better off building a frame.

If you're a bit handy with carpentry, I've also seen frames that are built on a stand that has a couple of levers so that you can toss material on it and then grab the handles to shake it out. I think I saw it used at an archaeological dig site, but from what I could see the construction looked fairly simple.

Details

A couple of things that I didn't mention above:

  1. The sifter should be designed so that rocks come out easily -- you don't want a fully enclosed frame, because then you have to tip it over to dump out the rocks.
  2. Ideally the sifter will be inclined -- the rocks will just fall out instead of you having to remove them.
  3. Decide where you want to have the sifted soil land (e.g. wheelbarrow, container, or the ground) and design the sifter around that destination. For example, if you want to capture soil in your wheelbarrow, make the frame wide enough so that it sits on the wheelbarrow edges, tilted so that you lose the rocks between the handles, and not so high that it will tip over your wheelbarrow.

Photos / References

This site has some photos of a simple frame sieve like mine. He built rails so it's easier to shake. (I've used a pair of sawhorses as rails instead of building a special jig.)

Here are detailed plans for a simple frame.

Here's a youtube playlist that has several different styles -- flat shakers and rotary style, manual and motorized.

This one is on a stand as suggested by Ed Staub in a comment below.

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Nice post. Are you thinking of a frame on the top or the bottom? FWIW, I've used a 2x4 frame on the bottom of the screen that fits over a wheelbarrow, with a 2-3-inch lip at the front and back to allow rocking. But for this big job, I think you're right about making a sloped screen. A minor point: I suspect the suppport (sawhorse) has to be fixed in place somehow. If the frame's on the bottom, and fits over the sawhorse, that would do it. One final thing: consider raking out grass, etc. first; it will tend to clog the screen and be a nuisance. –  Ed Staub Nov 23 '11 at 14:14
    
@EdStaub: I used 2x4s for the top, and strapping (~1x3) on the bottom to hold the screen in place and make it sturdier. I agree on fixing the screen to the sawhorse/support -- bolts or something so it can swivel/pivot. –  bstpierre Nov 23 '11 at 15:57
    
Thanks bstpierre for your answer! I would love to see some photos of examples –  Highly Irregular Nov 27 '11 at 21:53
    
We have a stiff wire that has holes smaller than chicken wire, in a wooden frame. That is set on top of two saw horses, and soil is shoveled on top, over an area that already has good soil. Wearing thick gloves, we manually sieve it and let the good soil drop. Then the remaining rocks are put into a wheelbarrow and moved away. Repeat until you have some VERY nice non-rocky soil (and a pile of rocks). It's hard work, but it does work. –  thursdaysgeek Nov 29 '11 at 0:03
    
I have a similar problem, and have concluded that the rotary one, called a trommel, looks like the way to go. One guy to spin it, one to shovel in. Or rig up a motor to a car battery.instructables.com/id/Trommel-Compost-Sifter –  Oliver yesterday

Soil is nothing more than little rocks...plants do not have a problem with a few large rocks. I've seen expensive, custom-made soils that were made with a significant percentage of pea-gravels. My rule which was made by someone else is to toss any rock larger than my fist out of the garden. No matter what your soil composition is, the only way to improve it is to add DECOMPOSED organic matter...and just put the mulch ON TOP. The soil organisms eat the stuff and crawl back into the soil profile, pooping matter out, mixing it into the soil for you.

Gotta relax a bit...sifting soil is awfully un-fun and humans don't like repeats of un-fun things-to-do. A few rocks is no big deal. You are going to need an awful lot of DECOMPOSED ORGANIC MATER to mix into your soil...hopefully it isn't all rock and no true soil. That would be another problem altogether.

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You're right on the mark that it's "un-fun"! It is worth mentioning though that soil should be much more than just little rocks (as you say, the organic matter is important) if you want your plants to grow well. I think we're on the same page, but definitions are important! –  Highly Irregular May 8 at 3:42

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