The only "cure" for clay soil is organic matter, lots. Whether gypsum would be of any use depends on whether you have a sodic clay soil, one that accumulates salts because of lack of rainfall and that depends on just where in New South Wales you do live.
Just concentrate on adding organic matter, any vegetative waste yuou can get, to that clay since that will seperate the clay soil particles so they cannot stick together as if glued.

Did you use the soil that's on site to fill the beds or did you bring something in? If you brought in a clay to go on top of a sandier soil, that can cause some pretty nasty problems for water movement at the interface of the two materials and there isn't a whole lot you can do about it whether you add organic matter or not. If the planters are filled with the same stuff that is on site or a material of similar texture, don't dig it out. In that case, the fact that the beds and native soils are the same texture will work in your favor.

As mentioned, clay does not equal a need for gypsum. A soil test that includes sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP) will tell you whether you need gypsum or not. If you find you've got an acidic soil that needs some pH adjustment, an addition of lime can also satisfy the calcium requirement while addressing the acidity in some cases.

g'day mary,

did you fill the beds with clay soil as has been asked? if so why the idea of raised beds is also to not have to work with or be concerened about the soil that is on site.

as ahs been said you need to add lots of organic matter, and for the most of us gypsum will help as we all mostly have the clay that will respond, you can do a simple test get about a golf ball size sampl of the clay and place it in a good cover of water in a bowl or small bucket for 24 hours if it is the type that will respond to gypsum then it will be dissolving or at least looking like it will.

i would suggest if it is not the right sort of clay that you may have to remove some or all depending on how much of it is in the beds??

we have pictures and story on our site on how we do our raised beds might be some ideas there for you?

len

Here is a link that might be useful: len's garden page

Southwest Idaho is an arid place, a desert. A nursery company that was founded here in Idaho sells a product designed for local conditions. They call it Huma-green and it is humic acid. I had used it for a few years before I looked into what it actually was. Previously, I had believed it was a fertilizer. So, for several years I was treating my acre property with this product without adding any fertilizer at all.

The grass was doing fine. When I started a new garden bed and dug up the sod, the top layer of soil was friable, looking like it had been worked by earthworms. It was the result of the humic acid. There were few earthworms to be found in my sod and topsoil, but the soil looked like it would be ok for gardening.

I'd recommend something similar to condition your soil. Of course, organic material will have humic acid in it, but if you wanted to jump-start the soil conditioning without waiting years for OM to get the job done, look for something similar to the Huma-green that we have.

Here is a link that might be useful: Wikipedia entry on humic acid

Not sure if Mississippi in southeast US compares to NSW clay soil, but I have had to learn to work with this since moving here last 2 yrs. The key is to dig your planting holes when the soil is moist. The best time is a couple days after a moderate rain. Do not work the soil if it is too "muddy" and "gloppy." Do not work the soil (almost impossible without an axe or pick) when it is very dry. When it is moist, it will be like chocolate cake. If it does not rain you will need to irrigate the area. In the meantime, and as often as possible, add organic matter and also mulch your plants. Dig your planting hole about same depth as container plant (if using a perennial for example, but twice or three times as wide. Scrape around the bottom and sides of this large hole so that roots can penetrate. Coming from an area with rich delta loam, I have had to learn clay and I am having success after learning this from the local garden experts and plain dirt gardeners like myself. good luck.

People that sell you "Humic Acid" products are selling you something for a lot of money that you can more easily get by adding organic matter to your soil. I think people that sell that kind of stuff are like the salesmen of old that sold "Lydia Pinkhams Magic Elixar".

I was expecting the person saying g'day would be from Australia, because the Australian gov't has a very good website about clay soil. Just haul in enough sand to get a ratio of 20% sand, 80% clay. Mix well with a garden fork to a depth of of 10 - 20 - 30 cm (up to a foot, or even more if you can). Ammend the soil with rotted cattle manure or compost or leaves or whatever will earthworms will eat. Your problem will be permanently solved. I have clay in my back yard and that is what I do. Do a google search for Australia clay soil and you'll likely find the site.
It's a government department of agriculture website. Adding just compost only will do nothing permanent, and your soild structure will still be clay. Add the sand and compost and you will have nice well structured soil forever. Better yet, if you have a source of silt, that would be perfect, but it becomes tricky sourcing out pure silt. We actually have some pure silt soils in this region, and one farmer who supplies "topsoil" is actually supplying 100% pure silt, cheap too.
Paul Mozarowski.

I read it 8 months ago, published from Australia, but I cannot locate it with google. Unfortunately my o/s was reinstalled and my bookmarks got lost. Opposite technique of adding clay to sand is well known. My place has beach sand over clay in areas. I excavate the clay and work it into the sand.
Paul Mozarowski.

I have very heavy clay soil here in New England, and I'm a firm believer in peat moss. I know not everyone will agree, but I've found that mixed with my native soil it does wonders to lighten it up and is super easy to work with and is really quite inexpensive (about $6 for a medium sized "bale").

Of course, compost is always the best option, but peat moss is a close second in my book! :)

If you add sand to clay, just make sure that you add enough. If you don't add enough organic matter, it will help, but not as much as adding enough OM would help. If you don't add enough sand, it can actually make things worse.

The advantage to adding clay is that the change it makes is permanent, and the change from organic matter is temporary.

Try to do something renewable, use wood chips, just pile them on, they work wonders, especially if you can get them for cheap or free. Peat is very much a specialty product and it should be reserved for those cases where its special properties are put to best use, such as propagation of cuttings, preparing a seedbed, something like that. Wholesale amending of soil with peat moss is wasteful. Please respect the earth and her finite resources, she will pay you back, one way, or the other, it's up to you. Paul Mozarowski.

Adding 20 percent sand, by volume, to your clay will do very little to help, every agricultural research university up here will tell you to start at 45 percent sand by volume and Cornell will tell you that should be 75 percent sand to clay. Organic matter is readily available, often free, and is much better for the soil, all else considered, than the sand which is simply more mineral and provides nothing for the soil bacteria to live on. Why anyone that lives someplace where tree leaves are available, free, would pay money for peat moss is beyond comprehension. If one lived in Arizona that may well be diferent.

I agree with kimmsr. Add large quantites of organic matter. Pass on the sand. Clay is a nutrient rich soil, and when you get enough organic matter worked into the soil, it will reward you with micronutrients. Test your Ph--often times clay soil is acidic and requires lime.

Just composting grass clippings, shredded leaves, and kitchen waste will give you all the inputs you need (except probably lime).

I'd recommend the peat moss as well, if it's available for cheap in your area. I've found nothing better for clay soil than peat moss.

If someone had nothing else available then maybe, possibly peat moss might be a choice but since it has no nutrients whatsoever and the soil bacteria will not munch on it, and you will need to add something else to the soil to feed the Soil Food Web, why bother.
Aside from the simple fact that peat moss is a non renewable resource.

I've used peat moss as well, it makes my clay soil less brick-like. I also add composted manure.

possibly peat moss might be a choice but since it has no nutrients whatsoever

But it does absorb nutrients from other sources that would normally leach out of the soil. Mix it half and half with manure and you have the perfect combination!

and the soil bacteria will not munch on it,

They will munch on it, just not as fast as compost. That's why peat moss stays in the soil for a couple years instead of disappearing in a couple months. It's a long lasting soil conditioner.

Aside from the simple fact that peat moss is a non renewable resource

Well that's not exactly true. It depends on how well managed the harvesting process is.

I know no one else has suggested this, but I fought with a clay soil bed for 6 years. I amended, and amended and amended. Almost broke my back! And nothing grew well. Finally, I had a landscaper dig it out to 24 inches and replace it with good topsoil. Today it drains beautifully and grows anything. While I add compost and other amendments to all my gardens annually, because it's better than fertilizer, I will NEVER try to correct a clay bed again by just using amendments. It's just too hard. So I guess what I'm saying is: If your bed is really bad, then maybe trying to do it yourself is more than you really want to take on. Just a suggestion.
MacThayer

There is a separate thread about adding sand to clay you might read. It certainly is not a given that adding sand is bad for clay, and adding large amounts as suggested by many web sites could be worse than adding a little.

I've improved clay soil with sand in three gardens so far, and each was much imporved with 10 - 20 % sand. Adding organics is also a requirement for really good soil.

macthayer said ...

... but I fought with a clay soil bed for 6 years. I amended, and amended and amended. Almost broke my back! And nothing grew well.

It is almost as useful to a gardener to know what has not worked as to know what did. I know you would probably as soon forget those six years of fighting the clay, but it would be of service if you would go into more detail on what the clay was like and the type of amendments that were tried over the years.

"I amended, and amended and amended. Almost broke my back! And nothing grew well."
I have Eastern Washington gray clay, compacted from years of livestock grazing and walking on it, and had never encountered it before. My first season in this house started in February '09, by July 4th I had ruptured my L-5 disc and herniated my L-4. After spending months with a pick, digging bar, garden weasel, mini tiller,truck loads of compost, grass clippings, anything I could till in, and a ton of vicodin, I gave up and had surgery to repair my back. I spent 6 months recovering and resting and am raring to go. This time I'm done fighting the soil and instead am going to lay cardboard down, do the lasagna thing and enjoy myself while planting in raised beds that sit on top of the clay. That way they can drain!