Wednesday, September 8, 2010

Soil Myths #3: Clay Breaker is not always your best friend

Too much gypsum can be a pain in the butt! Gypsum (calcium sulphate dihydrate: CaSO4.2H2O) or more commonly known as Clay Breaker, when used in large quantities can cause all sorts of problems. I was reminded of this in the last week as I worked on adapting a method to deal with gypsum interfering in nutrient measurements. Too much gypsum makes it difficult to measure nutrients, such as nitrogen. Gypsum is a type of salt, and for humans, plants and soil to much salt can be bad for health. So why are we recommended to use Clay Breaker? Do you really need Clay Breaker for your yard? Or are the Fertiliser companies ripping you off?

Why use Clay Breaker?

Clay Breakers or Gypsum are used to literally break-down clay. Traditionally, gypsum was used on heavy sodic clays in agricultural environments. These clays have a high content of sodium which reduces the porosity and water retention of soils, and hence plant growth. Soil scientists call this problem Sodicity. The calcium present in the Clay Breaker swaps with the sodium in the soil, and helps to bind the soil together. It improves porosity and water retention of soil, and thus plant growth also improves.

In your own backyard, you would use Clay Breaker in a similar way. People often use Clay Breaker when starting or improving a garden. In Australia, including Canberra, we often have heavy clay soils in our backyards. Gardens can be sparse, as there is not enough water in the soil for even grass to grow! So, when thinking about putting in a veggie or other garden, Clay Breaker comes to mind as a way of getting more moisture into the soil and improving plant growth. However, it isn't always the best option...

Example of a sodic soil; with a hard surface that plants can't get through!

Why is Clay Breaker not always the best option? 

Gypsum targets a specific type of soil, not necessarily the one in your backyard. Gypsum is great for targetting problems of sodic soils. However, not all clays are sodic! In fact, in Australia most sodic soils are found in river terraces, plains and in drainage areas; areas where sodium builds up from water movement and where sodium is naturally occuring. Some researchers say Sodic Soils make up about 28% of Australia. This means that the soil in your backyard may not necessarily be sodic. In fact, your soil may actually have heaps of calcium to help bind it, and this is when Gypsum may cause problems!

Gypsum can be unkind to your plants. Soils have a natural amount of salts present; natural salts of Calcium, Magnesium, Iron, Sodium etc. When you add Gypsum, you increase the salt content of the soil. If you add too much Gypsum, you can cause your soil to become too salty. When this happens, many plants refuse to grow or some start to grow and then wither and die. They are intolerant to the amount of salt in the soil as a result of the Gypsum application. 

But do not fear!! It actually may be another problem causing your clay to have poor plant growth, and there are other ways of fixing it.  First, you can work out what is wrong with your soil, and then what to add to get better plant growth.

Does your backyard look like this? 
You may have a problem with compaction and carbon!

What other problems could it be and what can I do about it? 

If Gypsum is not what you need to use in your Garden, how can you tell and what else can it be? You can do a few tests on your soil to work out the problem and how to solve it!

Step 1: Is it Sodicity?
  • Pull out your pH kit. If it has a pH greater than 7 (basic), it may be sodic.
  • Now, get a dish and add 1cm deep of rain or bottle water. Place 3 pieces of soil (about 1.5cm diameter) into the dish and leave for 5 minutes. If the water goes cloudy, then it is likely to be Sodic. Follow the Cure below. If your soil falls apart or does nothing, go to Step 2. 
Cure: Add 500g of Gypsum per meter square and gently hoe into your soil. If you aren't noticing any results after 6-12 months, try adding a reduced volume of 100g. Take care to use it sparingly, or you may get problems with salinity! Don't be suprised if you have a failed crop immediately after Gypsum use. You need about 6-12 months for the Gypsum to naturally integrate with the soil and for the salinity to reduce. In addition, you can also add some organic matter (below) for nutrients and improving soil structure.

Sodic soil with Gypsum added (white flecks). 
This soil is very saline and has only a few plants growing in it.

Step 2: Is it Carbon and Compaction (or both)?
  • Get a dish and add 1cm deep of rain or bottle water. Place 3 pieces of soil (about 1.5cm diameter) into the dish and leave for 5 minutes. If the peds fall apart or stay solid (but you still can't get anything to grow), then the problem is probably compaction and a lack of organic matter. 
  • Now for the hoe test! Get a shovel or hoe and try to dig a hole. If you are able to dig a bit of a hole without too much strain you probably have a Carbon problem. If the hole is really hard to dig, and you can bearly go down a few centimeters, the problem is Compaction. Check out the Cures for each below.
Carbon Cure: Low carbon means soil does not bind together, and water holding is reduced. It also means there are less soil bugs and nutrients for your plans. Replacing carbon through mulches is the best way to improve this problem! Add a mixture of Mulches to your garden and rake/hoe in. You can get some guidelines about Mulch mixes from a previous post: Mulch ain't Mulch. You will need to leave it 6-12 months before you see any really good results! Growth and productivity may be a bit slow to begin with.

Compaction Cure: Compaction usually happens with house construction. Heavy machinery tamper down soil, and reduce the ability of soil to hold water, roots to get into the soil and bugs to cycle nutrients. The best way to deal with this is a bit of Hard Yakka, mixed with some organic matter! Get out the hoe and the shovel and dig as deep as you can!!! If you can, get a loan of a rotary hoe and get nice and deep! But don't forget to check Dial before you Dig first! Add some mulch mix (as above), and double it!! Again, it may take some time to see results, but it will happen.

And if you still want to use Clay Breaker anyway, limit it to 100-200g per meter square. Otherwise you  may risk killing your plants!

Sodic soil (middle) with no treatment and with different treatments of Gypsum and Mulches.

Before you go for the bag of Clay Breaker, ask yourself 'Do I really need this?' Don't give into the fertiliser companies! You may not need Gypsum/Clay Breaker, and in fact, you may be killing your plants. Instead, do a few tests and work out if you need to use Clay Breaker, or if you need some Organic Matter!

For more info on Sodic Soils, check out this neat Guide by Central West CMA.   And if you want to get some more Info on your soil, gypsum application and Sodicity, you can send it away to a lab for analysis. Always happy to answer questions.

Happy Spring Gardening!


  1. Question: For step 1, if it is cloudy, then it is likely sodic. If not cloudy, then not likely sodic. For step 2, it looks like whatever happens with the soil, as long as it is not cloudy, then it is either a carbon or compaction problem. Did I read that right?

  2. Thanks, Amanda! :)

    Yes - that is right. If you have a look at the Guide from the CMA, it has a good example there.

    Sodic soils are pretty complicated, and aren't just limited to what I have talked about here. For example, Sodic soils can also be acidic, but they will have dispersion (cloudy water), and will benefit more from a lime application. These are fairly rare, but I do have an acid sodic and saline soil at one of my sites.

    The best way to know if you have a sodic soil is to test for sodium. However, these tests are a good guide for backyard soil lovers.

  3. Jess, I completely agree with you about not giving in to fertilizer companies. I spent my university years working in a plant nursery, and we were strongly encouraged to pawn off any and all chemical additions to help 'improve' our customers' gardens. I did try to subvert my clients by encouraging them to make compost and to use organic solutions though.
    My cure-all for any soil problem is good old compost. I don't know if the clay soil in Montreal is the same as the clay soil in Oz, but regular additions of homemade compost has cured my mum's garden of clay-iness.
    My own garden, a mere 30km from my parents' home, was very sandy, and I've managed to turn sand into loam after three years of intensive home-composting.
    Also, despite growing only non-disease resistant heirloom tomatoes, I've never had to deal with late blight or any other soil-borne fungi, a fact I attribute to my continued use of compost.

  4. I am a novice at gardening and so I had a soils analysis done. I have to say that I thought I had clay, but it is actually silt loam! I do not have a problem that requires gypsum, per the lab, I have a compaction problem from buying a tract home. Gypsum is used extensively in my area to amend soil, and I am glad I took the extra step to test my soil. I will be adding some nutrients, but I am concentrating on increasing the organic matter and I expect this will have a better effect on my soil than haphazard and ill-informed use of gypsum. The lab confirmed that my soil is not sodic and that gypsum would be a waste of time and possibly detrimental.

  5. I got this comment on another page on the weekend, but thought it would be better to go here:

    Has anyone heard of making your own Gypsum?
    Apparently you can apply Calcium Nitrate, then after a few days apply Sulphate of Ammonia.

    The calcium and Sulphate form gypsum, leaving Ammonium Nitrate to fertilise your grass.

    Apparently this is more effective than gypsum as a clay breaker (presuming the problem is sodicity - thanks for your Blog!!) because Cal Nitrate and SoA are both very soluble and travel further into the soil profile than the basically insoluble applied gypsum, which sits on the surface.

  6. Kathy, yes! People do use it, and it has mixed success. People generally don't use it in Australia as the nitrate/amonium rates are very high and can kill plants.

    You don't really need the Sulfate either, it is the Ca that you really want. You can make it more soluble by reducing your pH as well - down towards neutral. This can be done through nitrate/organic material etc.

  7. Hay Jess. Thanks for the info on gypsum. After reading through, I believe I have compacted soil around my house. My issue is my lawn. I have spent far too much money on fertilisers and water trying to keep the grass alive. The soil just below grass root level is extremely clay like and very compacted. The only thing i can think of doing apart from ripping it all up and starting again is to use a smallish rotary hoe and drill a hundred or more holes through my lawn and fill them with a sandy loam type soil. Looking for ideas and all feedback welcome.
    Cheers ....Dan

    1. Grab a lawn aerator from a hire shop. It does just that cores many small plugs from the lawn approx 30-40mm deep and spits them on the lawn. Then mow these up and topdress with some sand and CK88. Also suggest some wettasoil/ Penetrade or the like then water well.

    2. Have a read of this:

      The best way to aerate your soil is to get your soil biology happy! Organic matter for food and aeration, and improving moisture holding capacity is the key!! :D

  8. Sorry I meant Post hole digger or Earth Auger not rotary hoe... Dan

  9. I have a compaction problem. We bought a new house on a block of land that used to be sloped until heavy machinery dug it flat. When we first moved in there was literally 1 or 2 cm of top soil that came with the lawn followed by hard orange clay that you couldn't dent with a shovel.

    I've been digging my garden with a mattock for 3 years now gradually getting deeper each time. Roses grow really well in my garden now but I will be thinking seriously before buying another block with this type of soil.

    1. How frustrating! There is still alot you can do.

      I would break up the soil in the top 20cm and add organic matter. Organic matter (mulches and compost) and getting the soil biology is the key to growing plants, and beautiful soil!

      Hope it goes well

  10. is it possible to grow peach trees or grapes
    on a gypsum soil
    the soil is white turns brown when it gets wet
    and mostly powder

  11. Interesting comment about salt and health. As always some truth. Calcium sulphate is a salt but not the salt that we know as a food additive. This is sodium chloride. See this
    The old story a little knowledge is a dangerous thing!

    1. Thank you! You make an interesting point - and certainly NaCl (table salt) is totally different to Gypsum Salt. I was attempting to make an analogy - too much table salt is bad for humans, too much salt to soil (in form of gypsum) is bad for soil too. I will have to try and make that clearer. Many thanks.

  12. Hooray for a net entry on clay relevant to Canberra! I live on the western side of the Woden Valley and the clay soil here is hard, does not break down when immersed in water for days in a jar and the best way to dig a small hole is with a cold chisel and hammer. Gypsum does not appear to work. There are patches of ground on the footpath which remained bare since an optical cable went through in the late 1990s. Consistent watering along with some chipping it up and addition of old lawn clippings have recently covered some of it with grass but only some.

    At present I have a barrow half full of of equal quantities of this clay and composted leaves mixed with water. I shall see how that goes.

    Quite a change from the black, cracking clay where I used to live.

  13. Re the comments from Anonymous. A "salt" is a chemical compound of any acid with any metal or chemical group that acts like a metal such as ammonia- so the general term includes uranium nitrate, iron sulphide, sodium chloride, calcium sulphate, ammonium sulphate and so on and on. Obviously you don't want some of these in any soil.

    The colours of clays are largely controlled by the amount of iron in the compounds in the clay and the exact chemical state of the iron, and because the iron is chemically part of clay particles it cannot be removed. I very much doubt that the colour is any guide to the the fertility or otherwise of the clay. Very white clay though is unlikely to be fertile, good for porcelains, perhaps.

  14. Hi Jess. I have read all the above and its all very interesting and certainly relevant to my problem with a couple of exceptions. One is the clay soil here is a reddish colour and has a multitude of little and large rocks amongst it. It has been very hard to dig up. I have dug up a mound of this 'stuff' about 3mtrs by 3mtrs wide down about a mtre to try and get it ground level. Before this I was told to put gypsum down which I did. It did nothing but due to the amount of stones in the clay didn't help. After a week of digging I spread it all out over the lawn as it is. I was also told Lime would help. I have not added any lime at this stage. I tried to grow veges before I dug up the mound of clay and yes as above the growth was stilted and they just died even after fertilising every week to 2 weeks.
    I live on a Island off the Redland Bay area about 200mtrs from the boundary of mud and where the tide comes up so soil is salty as well. My front lawn is 'grassy' but plants I have planted there a mth ago are now showing stress signs with leaves on the shrubs ripping and yellowing. I water and fertilise and the past week seems everything is starting to die.
    Do you have any info that can help me. Even tho the front lawn is grassy and green the back where I dug up isn't. Only in patches here and there. Eucalyptus tress and Tee Trees grow well and shoots of the Eucalyptus trees are coming up everywhere which is just annoying. They are everywhere.
    Can you advise me on what to do please. It seems those who have really nice gardens here use topsoil as nothing will grow otherwise. This is what some say but don't want to spend money on soil if there is a better option to he the soil somewhat. Is there a type of fertiliser I can use for the existing plants?.
    I will add I do have several natives I planted in the soil when I came here and they are actually all doing well. Some of them (trying to remember name of them) are a bit slow but still look great so some natives and shrubs do well.
    Thks heaps for any help or suggestions. I would really appreciate it.

    1. Hi Lori,
      Sorry for the late reply!
      It sounds like you have naturally salty soils, and the only thing you can really do is plants things that like salt! Saltbush, natives in the area etc are all ok. If you want to grow other plants, like vegetables, you will have to get topsoil or used raised beds above the natural soil and groundwater. As you live in a tidal zone, amendments won't work to reduce your salt problem - it will be permanently salty.
      Lime is also unlikely to help and same with gypsum - it is adding salt to more salt.
      Sorry I cant help further without some soil tests -- but I suggest raised beds is the way to go and native salt tolerant/local species.
      All the best,