pH in Soil s for Landscaping and Garden Use

I recently had 6 wicking beds built, and the landscaper brought in “organic veggie mix” from a Soil and Landscaper business in Dapto. Before adding anything else, I tested the soil and found it to be a pH of nearly 10 - very, very alkaline. I don’t think anything will grow in this mix. pH of 6.5/7 (“Neutral”) is best. Gardening friends tell me it may take months, if not a couple of years, to get the pH down to acceptable levels.
The AS is 4419:2018, however I cannot find any information on this in regards to pH, without spending a couple of hundred dollars on the document. Would anyone know of my rights? To my mind, this “organic veggie mix” is not fit for purpose. Would appreciate any knowledge out there before I contact the supplier direct (landscaper just tells me to chuck a few bags of cow manure on, but I know that will take a long time to lower pH).
Thank you, Jodie

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Was the soil sold as certified under AS4419. If it wasn’t or ‘had the ticks’, it won’t apply.

For AS4419, for all soil classes, the guideline pH is between 5.5 and 7.5. Soils can have pH outside this range if marketed as such…for example mix for alkaline or acid loving plants.

How did you test it?

Different home testing methods have limitations. The only way to determine pH is using laboratory testing techniques like those outlined in the Australian Standard…for by soil testing laboratories.

How was the product sold?

Was it sold as a soil or a soil conditioner (such as compost added to an existing soil)?

What information do you have about the soil (such as indicative test results) and its claims?

Answers to the above questions will give information on what avenues might be available moving forward,


Hi, I used two different kits - a Manutec (which I got last year) and a Searles. So home kits, which I have used in the past and also compared to a friend’s kit when we were testing the soil at the front of my house.

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That is correct. Adding sulphur (the usual method of lowering pH) is always a slow process, it will depend on the buffering capacity of the soil how slow.

I agree with that. You should be asking the landscaper in writing to remove it all and replace it with something that is suitable. I am betting you paid a fair bit per metre for this soil and it should be right.

Before getting carried away, how did you measure the pH? This is a key datum for your case. Depending on how the landscaper reacts, if you haven’t already done so, you may have to get a laboratory report.

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It was sold as an “Organic Veggie Mix”. I haven’t called the supplier yet as I wanted to have all my ducks in a row and know what my rights are. I don’t want to be fobbed off. Thank you


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These are both field indicator tests and possibly use barium sulfate powder to absorb the indicator.

If the soil is high in organic matter, soluble organic materials which are often dark in colour can impact on the indicator colour, making it appear deeper and darker than it otherwise should.

It doesn’t necessarily mean the result is wrong, it just may not be reliable.

Have you asked the supplier for indicative test results for the mix?

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I’ve just used two home testing kits. I’ve used these before, and in conjunction with a very experienced friend’s kit to compare our results. Photo hopefully attached.


Thank you, that’s good to know. I will call the supplier and ask if they test their soils. Cheers

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Also confirm what you ordered and was delivered.

pH in organic materials is complex and can change significantly over time.

With organic materials, they can fluctuate from acidic to alkaline depending on the stage of the composting process.

A soil showing a pH of 10 is highly unusual, even for a manufactured soil. Usually such high pHs only occur when a alkalising agent/ingredient has been added to the soil, and the soil is measured immediately on its application before it has had time to react with the soil.

Being pH 10, I suspect that either the kits aren’t designed for testing of high organic soils or an alkalising agent (such as lime) had been added just before its delivery. If it is the later, depending on weather conditions, the lime should react reasonably quickly with the pH stabilising also reasonably quickly.

Hopefully if the particular batch of soil wasn’t subject of a soil test, the soil supplier/manufacturer will take a sample and have it tested by a laboratory. The test is reasonably inexpensive with a fast turnaround and will give a more accurate idea of the mixes pH.

In the interim, it may be worth planting some seed of something which grows fast and in the cooler months to see what happens. pH 10 is usually at the cusp of where germination and plant can be impacted. Growing a fast growing crop in both the soil and an adjacent area where soil is known to be okay (as a control) can give indications of if there is a problem.


That is a real possibility. Another is that the soil was not mixed very well after liming and there are pockets with extra lime that the OP happened to hit. If the maker is dinkum they ought to be able to give a sensible explanation. If the problem is the first the measured pH ought to fall noticeably without intervention in a few weeks. If the second, doing more tests from different locations and depths will show pH readings all over the place. However, if the apprentice added the lime at the yard and put in far too much the soil will need to be replaced.

I am somewhat a fan of the Manutec dye indicator test. I have used it for years and never seen any anomalies, it does seem to be cheap, quick and accurate as in the advertisements. It even works for someone inflicted with genetic protanomaly! I have previously tried to find any reliable testing of the accuracy without success.


A quick acidic raiser is Sulphate of Ammonia, often used to kill weeds on direct application, or Super Phosphate is another one. Both will lower pH fairly rapidly but larger application may be needed with such high pH. After application you will need to let the soil rest for a week then retest. If needed apply more of the product. Note that Super may inhibit earthworm activity quite drastically.

Another possible cause of such high pH is the use of Mushroom compost or large doses of chicken manure both are quite alkaline.


I’m not sure where you are with this issue Jodie - given the time frame. but here’s some further information (for you and others who may be interested).

  1. Colour pH kits like the ones you use have accuracy limitations depending on the materials being tested.
  2. I recommend using a pH meter - costs maybe $50-150 for portable pH probe. It has a glass tip, so need to take care of it, but with care can give several years service. Also useful for general gardening, if planting acid-loving (e.g. azaleas, camellias) or lime-loving plants (e.g. paeonies).
  3. Alternatively, look for a local lab, or see if a local school or college that has science department, will test pH for you, preferably using a method similar to AS4419.
  4. Comments already made by others about the soil being mixed are very valid. If you want an overview, collect your samples for testing from 5-10 or more places in your wicking beds, blend these thoroughly, then test a subsample. Otherwise, if you want to assess pH variance, test samples from different places separately.
  5. There are many causes for high pH, as others have already mentioned, but it must be borne in mind that pH changes over time, depending on many things (substrate, fertilisers, water quality & frequency, etc).
    Adding manures or other urea-containing fertilisers can initially increase the pH (as urea is broken down to ammonium carbonate), then decrease the pH (as ammonium is used by plants). [It’s important to read the fertiliser label for nitrogen composition as nitrate, ammonium, urea, or ‘organic N’]. With this in mind, your soil supplier may have dosed the soil up with urea or chicken manure thinking he’s doing customers a favour, but the down side can indeed be a transient high pH, then quite a low pH! Or he may have (knowingly or unknowingly) used a limey component.
  6. Soil providers made supply ‘certified’ AS4419 soil or AS4419 ‘compliant’.
    If it’s ‘certified’ then the manufacturer is regularly checked by an independent authority that the soil & the relevant company processes meet the standard on an ongoing basis.
    If the soil is merely ‘compliant’, it may just mean that the product or formulation has been tested to AS4419 requirements once or twice, with no ongoing, independent monitoring.
  7. If the pH is in reality very high (and staying high - not dropping naturally), then you can acidify the soil using powdered sulphur (takes a long time - many months), ammonium-based fertilisers (quicker, but can still take weeks-months), ferrous sulphate or even citric acid or vinegar. The last 3 are quite fast, but require care and diligence to not overdose - otherwise you’ll have the opposite problem - low pH. The amount of any acidifier will depend on the ‘buffering capacity’ of the soil.
  8. Finally, but perhaps most importantly, products must be ‘fit-for-purpose’. If the soil does indeed have pH 10, or is otherwise not fit for purpose (e.g. plants don’t survive), then you have recourse to take action (refund or replacement).
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Thank you very much for your detailed reply! Sorry I dropped out of the conversation, we’ve been very busy with work and the garden and renos.
I actually did send a sample away to be tested (SESL) and it came back at 7.74. I was astounded at the difference between my results and the professional testing. You are absolutely correct in (1) above; these kits are not accurate. Very disappointing. However, I was overjoyed that I could begin planting in my beds, had already given them a dose or two of sulphur (which will not hurt given the tested soil is still above neutral).
Many thanks

By all means get a glass electrode probe but stay away from the metal electrodes as they are not accurate.