Soil improvement for clay?

mad_gardenerFebruary 6, 2009

I live in the land of the red clay, in a subdivision where any topsoil has gone the way of the bulldozer. Lately I've been trying to think of ways to improve the clay soil that I'm stuck with in my 1/4 acre yard (I do have raised beds for vegetable gardening, but I have dreams of a lush backyard that could act as a small slice of heaven for the local wildlife). I've heard of laying down newspapers and growing cover crops, but can anyone describe either method in detail? I'd also like recommendations as to the best cover crops to grow to improve clay soil. Please note that since I live in a subdivision, I would like to try to avoid cover crops that could easily become invasive and spread to my neighbors' yards.


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I have a similar situation. I live on a 1/4 acre and it is clay and rocks. I started adding organic material both by top dressing and by mixing organic materials in with soil. Now it is like a different yard. The grass is denser and healthier and the plants are finally filling in. The best source of organic material that I have found so far is vermicompost. I used the directions to build a bin and how to properly use vermicompost. All of the information was on This is definately the easiest way to compost your waste and vermicomost is much heathier than compost.

Here is a link that might be useful: Vermicompost Guide

    Bookmark   February 7, 2009 at 12:11AM
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The only thing your clay does need to make it better is organic matter, compost and about any other vegetative waste you can put in there. Whether that needs to be vermicompost or just regular compost can be a subject of much debate, but both are good. The leaves from those deciduous trees that grow in Georgia as well as cover crops can be one source of that organic matter.
Cover crops, some kind of plant you grow to aid in soil stabilization, would be one way but that usually takes a growing season during which you really have a grain crop in your yard whether what you plant is some kind of pea, oats, buckwheat, alfalfa, or any other common cover crop.
Covering the soil with newspaper, meant to deprive the plants growing in the soil now from access to needed sunlight, and then covering the newspaper with a mulch to hide the paper and keep it in place can also be a way to convert a soil. As the plants that grow there now die they contribute organic matter to the soil and help feed the soil bacteria and as the paper and mulch is digested that adds organic matter to the soil too.
Tilling what is there now in along with more organic matter can also be an option and has the added advantage of helping you get the soil ready for planting this year whereas the others may mean not until next. But tilling can be a lot of hard work and will disrupt the life cycle of the Soil Food Web for a time, and will not do quite as good a job of mixng organic matter into the soil as that Soil Food Web would.

    Bookmark   February 7, 2009 at 6:43AM
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billhill(z5 MI - KBG)

Orgarden - You are incredible. All your posts since you recently registered give the same message. STOP mongering these forums promoting your commercial enterprise website.

    Bookmark   February 7, 2009 at 7:08AM
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Bill, if you visit the website orgarden links to, there is NOTHING of a commercial nature contained on that is simply instructions on how to build a worm bin, begin vermicomposting and utilizing the compost. Ease up, guy!! orgarden is just very enthusiastic about vermicompost, whch is indeed a good thing.

    Bookmark   February 7, 2009 at 10:07AM
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As others have said, organic matter is the key. You might alos look into garden grade gypsum which is ised for breaking up hardpan and loosens the soil.

The Garden Guy
"Read articles & journal entries"

    Bookmark   February 7, 2009 at 10:27AM
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dchall_san_antonio(8 San Antonio)

Dutch white clover is a good crop to grow to enrich the soil. Be sure the seeds are inoculated with the proper microbes first. The microbes inoculated onto clover seeds will develop storage for nitrogen. The source of that nitrogen is the air and not other fertilizer sources. Mulch mow the clover at 4-5 inches high. Actually if you leave it at 5 inches, that's about as tall as the Dutch white variety will ever get, so you don't have to mow it.

Anything else that puts roots in the soil is putting organic matter in the soil. Roots are organic matter and the microbes that feed them when they are alive and decompose them when they die is all beneficial. You can also feed those microbes with organic fertilizer (fertilizer, not compost).

    Bookmark   February 7, 2009 at 5:20PM
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Thanks for all of the tips, especially about the gypsum & dutch clover. As to introducing organic matter via compost, perhaps I should have specified that I already have a compost pile. Unfortunately, production goes slowly, partially because the majority of what we compost happens to be hay from our rabbit's litter box, which seems to degrade rather slowly (we probably not enough green matter with the brown). There is a local Starbucks though, and though I personally detest their coffee I do have intentions of stopping by and asking their manager if I can have their grounds. As for the vermicomposting, we'll be checking into that too. A nearby retailer will be selling worms soon, so we're just waiting for those to mature so that we can pick some up & get cracking. However, I kind of doubt that the worms will be able to produce enough castings to cover the entire area that I want to enrich, which is why I would like to try going some cover crops to help speed things up. I'd also like to try gypsum, but when I did a little research on it last night there was one article that said that it could be a bit of a pollutant for nearby watersheds, since it tends to increase the leaching of aluminum. It also said that it increases the leaching of iron and manganese. Under the link below, look for "Myth: Adding Gypsum to your Yard or Garden Will Improve Soil Tilth and Plant Health". Has anyone else heard about the negative effects of gypsum? Personal experiences, anyone?

Here is a link that might be useful: Linda Chalker-Scott

    Bookmark   February 7, 2009 at 11:01PM
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Regarding the gypsum, I doubt that you would be using enough of it over a long enough period to effect any watershed. Used sensibly, it is perfectly safe.

Do worry if your compost is not completely decomposed! Incorporate it into the soil at any stage, and the microorganisms will quickly finish the job right in the soil. Even uncomposted organic matter quickly breaks down in soil.

The Garden Guy
"Read articles & journal entries"

    Bookmark   February 7, 2009 at 11:14PM
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The question is how long do you want your additions to the soil to last before they need to be replaced?

Organic matter is the traditional answer and it works, but it also decomposes and needs to be replenished annually if not more often.

Vermicompost is completely unrealistic. It is horribly expensive to purchase and takes a long time to make it in any kind of volume.

Mulched leaves (run them over with the mower a few times) are a good option and they should last a year or two.

If you want a permanent solution to a small area for growing plants then you want an inorganic, stable material such as Turface MVP which is simply a fired clay product that is fired at a high enough temperature that it won't revert back to mush when wet. It has an incredible internal porosity so it holds water and oxygen at the same time. It improves drainage and it is permanent. It is used on athletic fields and you will have the best luck finding it at landscape supply companies. This is something you would till in. It isn't cheap (about $10 for 1.6 cubic foot bag), but it's effects are forever.

Don't forget though that sometimes the best way to improve soil on a small scale is to build on top of it. Bring in good soil and make raised beds/rows.

Trying to make a clay/rock soil anything other than a clay/rock soil is, in my opinion, an exercise in futility. To the extent to achieve the goal you end up making swimming pools where the surrounding clay soil doesn't drain, but the improved soil does - until the water hits the unimproved soil under and around it and it then fills up with water.

Having said all the above, most of the time clay soil is a good thing, not a bad thing. It holds water and nutrients better than any other soil type. As long as it isn't seriously compacted or in a low lying area where water pools/ponds it should be great to grow in.

    Bookmark   February 8, 2009 at 12:04AM
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lou_midlothian_tx(z8 DFW, Tx)


I'm living proof that you can grow great lawn on rocks... From Before and After Lawn From Before and After Lawn From Before and After Lawn

I turned top 4-6 inches of white dirt into black stuff after 3 years of organic program. I went from zero earthworm to tens of thousands. Of course I bought some and I think that was well money spent. My neighbors still do not have earthworms after 3 years. I just apply organic fertilizer every few months. I used to spray molasses but not anymore as they don't really make much difference after 2-3 years. Compost should be one time only to get the ball rolling. All you have to do is fertilize with organic fertilizer. Mulch mow everything at 3-4 inches. Water deeply and infrequently and you will have nice lawn.

    Bookmark   February 8, 2009 at 12:29AM
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I have a clay soil as well and a (if I may say so) great lawn as well. I fertilize with nothing other than soybean meal spread at 10-20lbs per 1,000 sq ft a couple times per year.

Lawns are quite different than veggies though in terms of soil structure and drainage requirements. Lawns are also much different than large plants such as shrubs and trees.

A great lawn can be grown on nearly anything provided adequate water and nutrients, but the same cannot be said for veggies and most other plants that have more exacting drainage requirements. I have grass growing on/in rail road ties as much as I wish it didn't.

Since you posted pictures I do have a question. The first picture shows a more or less flat lot (relative to the streets) and the second picture shows a lot elevated a few feet higher. What was used to raise the lot well above street level?

    Bookmark   February 8, 2009 at 1:45AM
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Gypsum works if the clay soil you have is a sodic clay, and those types of clay are usually found in the more arid parts of the world. It is not likely that gypsum will do much more for Georgia clay than use up your money. Keith Baldwin, was a professor of Soil Science at North Carolina State Universtity, wrote an article in Taunton Press' Kitchen Garden magazine a while back about improving the red clay in North Carolina and about all he suggested doing was adding organic matter.

    Bookmark   February 8, 2009 at 7:21AM
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dchall_san_antonio(8 San Antonio)

I'm convinced that Linda Chalker-Scott makes up her own fantasy myths and then solves them with her own random thoughts.

    Bookmark   February 8, 2009 at 11:50PM
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rhizo_1 (North AL) zone 7

Chalker-Scott didn't invent the science, dchall. Gypsum won't do anything to clay soils, unless sodium contributes to the problem. Sodic soils are also found in coastal regions, as well.

    Bookmark   February 9, 2009 at 3:29PM
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I have a vegetable garden in heavy clay , I use expanded shale to break up. (good stuff)

    Bookmark   February 11, 2009 at 12:11PM
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kimmsr , I have seen gypsum used in clay soil in upstate NY, hardly an arid region, with good success, and it makes it easier to incorporate organic matter, which is the ultimate cure. I don't think it's a waste of money at all.

The Garden Guy
"Read articles & journal entries"

    Bookmark   February 11, 2009 at 1:38PM
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I think leaf litter can be the cheapest, best part of the overall organic matter + native clay equation. Fully rotted to be mixed in, partially composted as a top mulch. Tree species obviously matter, but I'm not expert enough to do more than generalize. The gigantic cottonwood up the street has been a huge help to me - dude lets me rake up as much as I want in Fall (and wishes I would do it more) and I use it everywhere, in my strange coffee grounds/bouganveilla bracts/pine needle/leaf litter mix I'm fond of using throughout the garden.

I would use cover crops as a secondary method of improving my clay soils. Just growing regular veggies and then turning new OM in the soil between crops has done wonders for some of my previous problem areas. And engineering isn't to be overlooked - building raised beds and giving up on that alumino-silicate muck can certainly work too. And good drainage to assure that your trees and shrubs aren't rotting in standing water.

    Bookmark   February 11, 2009 at 6:03PM
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Ron, was gypsum the only material added to that soil or was other material added at the same time?

    Bookmark   February 12, 2009 at 6:36AM
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Some compost was also incorporated at the same time. I know there was another area where only compost was used, and it took a couple of years longer to get good results. It seems that the gypsum made a significent difference.

    Bookmark   February 12, 2009 at 5:31PM
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The Calcium in gypsum is a bit more readily avaialable than the Ca in lime is, and gypsum does supply to the Soil Food Web some Sulfur, which may not be very readily available in soils with low levels of organic matter. I would bet, however, since what was in the compost is more readily available than what is in gypsum that the compost is what made the difference. Many times people compare that which is not comparable.

    Bookmark   February 13, 2009 at 7:19AM
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I don't know about that. Both plots got the compost, but the plot that got the compost AND the gypsum did far better. Weather it was the gypsum alone or the combination of the gypsum and organic matter, the effect of the gypsum was very significent.

When compost breaks down, the amount of humus it leaves is very small compared to it's initial volume. That's why it can take a few years to see big improvement. This is the same soil that was on my farm, and I can tell you first hand it took 3 years of heavy applications of organic matter to make it reasonally friable and fertile.

But there was a major improvement after the first year with the gypsum/compost combination. There is no disputing the gypsum made a big difference.

The Garden Guy
"Read articles & journal entries"

    Bookmark   February 13, 2009 at 5:11PM
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