How to: test your garden soil’s pH, and balance it for a better veggie harvest

P1020806 - Version 2

So you’re resolved to grow the best darn vegetables ever. You’re on a mission to feed your family nutrient-dense, organic, home-grown food, to stick it to the supermarket, and to hopefully have enough to share with friends and neighbours too.

Getting your soil’s pH balanced can help a lot. Here’s how to do it:

Why to balance your soil: to grow awesome veggies like these, of course!

Why to balance your soil: to grow awesome veggies like these, of course!

Why test my soil? Some/most of my plants seem to be growing fine:

Healthy plants should be able to get all (yep, ALL) of the nutrients they need from the soil.

But if your soil is too acidic or too alkaline, those nutrients won’t be available, no matter how much fertiliser you add.

Acidity has a strong effect on the ability of plants to take up soil nutrients as well as upon the wellbeing of soil organisms.

Most nutrients that plants need can be chemically assimilated when the pH of the soil solution ranges from 6.0 to 7.5.

  • Below pH 6.0, some nutrients, such as nitrogen, phosphorus, and potassium, are less available.
  • When pH exceeds 7.5, iron, manganese, and phosphorus are less available.

So getting your soil pH right is absolutely essential, if you want nutrient-dense veggies.

pH-Scale

First, the basics of pH

pH is a measure of the acidity vs the alkalinity of the soil, and determines the capacity of that soil to exchange nutrients with plants growing in it.

As well as affecting the ability of plants to uptake nutrient by both chemical and biological processes, the pH also affects the diversity and species of soil microbiology.

pH is usually measured on a scale of 1-14:

  • A pH of 7 indicates neutral soil
  • A pH above 7 indicates alkaline soil
  • A pH below 7 indicates acidic soil

Not all plants are the same – different crops prefer different levels of acidity – for example:

  • Strawberries will yield well at a lower pH of 5.5 to 6.5
  • Carrots love balanced soils pH of 6 to 7
  • Sunflowers thrive in soils ph 7 to 7.5

399-74728soil type

So it depends what you’re growing as to what pH you want to nudge your soils towards. Keep in mind that most annual veggies prefer a bacterially dominated soil, which is leaning towards a pH of 7 – 7.5

Soil science and the nature and intricacies of the soil food web is a VERY BIG topic. And an awesome one, too. But for now, let’s leave it at that.

Basically, if you want a garden bed that the majority of your veggies will thrive in, you want to create soil that has a pH of 7 – 7.5.

P1020806 - Version 2

How to test your soil with a simple soil ph test kit:

Firstly, get your hands on a soil pH test kit. These can be got from garden centres, or online.

We recommend the dye & powder system (scroll down the page) developed by the CSIRO ($29) , or Kelway Soil pH & Moisture Meter ($175) for broader areas.

  • Use a small sample of soil, taken 10-15cm from the surface, and put on a the mixing card
  • Add a few drops of the indicator dye and dust with the white powder supplied with the kit.
  • Wait about 30 seconds for the colour change to take effect. You will get a more accurate result if you wait a few minutes.
  • Use the colour chart to match the colour of your soil samples. Each color indicates what level pH your soil is.
  • If in doubt, wait 2 minutes and check again the resulting color
  • Take several measurements in different spots in the garden. A minimum of six samples from different parts of your garden is a safe amount.
  • A single reading may be an anomaly, so it’s good to get an idea of the average pH in a plot. If they’re all around the same, take the average and amend the soil accordingly. If one spot is very different than the rest, however, you may need to “spot treat” it.
  • Record your results in a garden diary. You may need to reference your test results at a later date, as they may change over time.
  • Test your soil annually to know exactly what your garden’s nutritional requirements are.
Keeping a garden diary is a great way to improve your soil and ensure you don't repeat common beginner's mistakes!

Keeping a garden diary is a great way to improve garden and soil health – don’t assume you’ll remember all those pH results just in your head!

How to balance your soil’s pH

So you’ve tested your soil in six places and you’ve found out that it’s generally a pH of… whatever it is.

Here’s some tips on how you can balance your soil…

If the soil is too acidic: less than 7 = low pH (applies to most Australian soils):

  • Add green manure crops into your rotation with more frequency.

  • Add organic matter in the form of a well balanced, pH neutral compost… adding humus is the best way of changing pH… let the biology do the work!!

  • Add agricultural lime (not builders lime!). As a rule of thumb, carefully apply 100g to each meter squared. NOTE lime can only be accurately applied if a total mineral test is performed. It will take a while to increase the pH this way – you should see a change in the pH within 6 months. Be careful not to over apply.

  • Add Dolomite – BUT it contains Magnesium, which if it is already present in large quantities, could block other minerals. Again, a total mineral test is a good idea before doing this.

If soil is too alkaline: greater than 7 = high pH:

  • This soil will be harder to rebalance

  • Add organic matter such as pine needles or decomposed tree leaves.

  • Add green manure crops into your rotation with more frequency

  • Add organic matter in the form of a well balanced, pH neutral compost… adding humus is the best way of changing pH… let the biology do the work!!
  • In an extreme situation you could use powdered sulphur. Be very careful with this as sulphur is anti microbial… and will kill off your biology if applied regularly. Apply one handful per square metre, once a year. It works very slowly and you won’t notice a change in your pH for about 6 months.

There’s other, more in-depth roads you can go down with mineral testing for your soil (we recommend Swep Laboratories if you’re going this road).

But as you can hopefully see from the info above, balancing your soil’s pH is a great first step to healthy veggies.

In short, balancing your soil’s pH is a short-cut to growing healthy food.

Once you’re on your way with good soil pH, it’s much easier to treat mineral deficiencies if they crop up in your plants.

Because now, you’ve created a soil environment where the plants can suck up the goodness they need, once you give it to them.

Michael Hewins and Milkwood Farm veggies

Michael Hewins and Milkwood Farm veggies

Lastly, if you live nearish to Sydney NSW,  join us for a Serious Backyard Veggies course with Michael Hewins sometime and learn more about making great soil.

Michael’s an amazing organic market gardener who’s passionate about de-mystifying the process of growing nutrient-dense veggies, starting with your garden’s soil.

Good books for further reading on garden soil health:

Good luck out there, gardeners!

May your corn rise high, your potatoes be fulsome and your tomatoes, berries and salad greens be so plentiful you’ve enough for everyone on your street…

Big thanks to Michael Hewins for his contributions on this how-to.

15 Comments

  1. Posted March 17, 2014 at 7:24 am | Permalink | Reply

    Reblogged this on Oldschool's Notebook.

  2. Posted March 17, 2014 at 7:46 am | Permalink | Reply

    Wow great post I’m going to have to try this. I always thought soil science was a mystery, but this makes it simple. Thanks!

  3. Shonah
    Posted March 17, 2014 at 8:45 am | Permalink | Reply

    Thanks Kirsten and Micheal you explained it so well that I actually ‘got it’. Had heard about balancing soils before but not fully understood why.
    Thank you again

  4. Posted March 17, 2014 at 9:25 am | Permalink | Reply

    Reblogged this on The Violet Verge.

  5. Posted March 17, 2014 at 9:31 am | Permalink | Reply

    Thanks for explaining this so simply. This might help my winter veggies meet a better fate than the summer ones!

  6. RogerC
    Posted March 17, 2014 at 3:09 pm | Permalink | Reply

    Wonderful simple explanation. Keep up the good work.

  7. Nicholas
    Posted March 18, 2014 at 10:33 am | Permalink | Reply

    Good info Michael but may I suggest (as you do with your comment – “let the biology do the work!!”) that we focus more on the biology than the micro/macro nutrients. You can make your soils acidic with fungally dominant compost and teas or more alkaline with a dominant bacterial mix/brew. It also becomes a more permantent change, plus you get the benefits of the biology acting as your nutrient sinks (especially nitrogen in bacteria). Just a thought as digging up lime and dolomite to put on soils is very high in embedded energy.

    • Posted March 18, 2014 at 1:44 pm | Permalink | Reply

      Completely agree Nicholas. The draft of this blog post included this information…. but for whatever reason it was edited out, im guessing because digging deeper into the biological side of soil web relationships can be quite complex in it’s nature and the common gardeners use and application of this knowledge. None the less, it is very important and should not be discredited simply because it seems ‘to complex’. Here is my own words on ‘the basics’ of how soil biology affects soil pH from the draft that wasn’t included in this article (ignore the bad grammar). This description is not just good ‘up to date’ knowledge but that to which I have experienced in my own personal journey of cultivating soil for human needs.

      —-
      HOW BIOLOGY AFFECTS SOIL pH
      As with any soil driven process, it is a relationship between the plant and the soil biota. How this affects soil pH is quite elegantly beautiful. Soil biology influence’s mostly the pH of soil within the rhizosphere, the site at which all the action happens within your soil.
      Soil biology…. or more specifically the ‘soil food web’ plays a major role in the pH of a given soil profile, particularly our ‘cultivated’ soils. Bacteria and fungi, two of the major foundational organism’s that drive the soil food web, together of which are the most common organisms found in your soil have a marked effect on soil pH. The presence of bacteria within your soil, when it is the dominant microbe tends to create a more ‘alkaline soil’. This is often the reason why we can see a marked change in pH in our new garden beds from starting out as acid. When we cultivate soil over the first few years of establishing a garden…. so often our predominant forms of cultivation are actually cultivating a mostly bacteria dominant soil profile. Bacteria change pH by exuding ‘bioslimes’ through there day to day activity.. these bioslimes are often of more an alkaline consistency. Bioslimes are sticky carbohydrates (polysaccharides) and are important soil structural building elements that glue and hold soil particles (soil texture) together but primarily are the bacterias way of glueing themselves into the soil profile and to each other to prevent being washed away.
      Fungi on the other hand create a much more acidic soil due to the organic acids and enzymes they release when an active member in a balanced soil food web community. These acids tend to be more on the acidic side of the spectrum, therefore creating a more acidic soil.

      When it comes to vegetable/annual gardening, it is known that a more bacterial dominant soil gives more of the ideal soil conditions for our hungry vegetable plants. But in saying that, it is important to have a balanced bacteria to fungal ratio for both the pH and nutrient cycling. When we have healthy populations of beneficial bacteria within our soil, we see that our soil increases in pH, and when the pH gets to its optimum range for vegetable gardening at around the 7-7.5 mark, habitat for certain strains of bacteria are created, particularly ‘nitrifying bacteria’ that have the ability to convert nitrogen in different forms to ‘plant available forms’.
      With the presence of these specific bacteria in the correct pH range, nitrogen uptake, that of which is vital for vegetable and herbaceous plants alike, is managed by the soil food web much more functionally.

      Plants that tend to prefer a certain range of pH, has as much to do with the chemical reactions occurring in the soil as what it has to do with the preferred forms of biology that the plant exchanges with in the rhizosphere through root exudates and other ‘feed and be fed’ relationships. Plants that prefer more acidic conditions often have a greater fungal relationship than plants that prefer a more alkaline pH. Generally these plants tend to exude certain sugars that are food to certain soil biology, in this case fungi. This goes the same for plants that prefer a more alkaline soil, they tend to have quite a strong bacterial dominated relationship.
      —-

      A final note. I believe strongly from my own personal experience that the ‘chemistry’ approach to balancing soil pH is still valid. It all comes back to the context of application. Working as a full time market gardener in a commercial environment see’s the context of adjusting chemical relationships in the soil important for commercial viability in the short term to maintain production and viability. I choose to approach both methods of balancing pH when contextually operating in both the backyard garden and commercial veg patch. Thanks for your comment :)

      Michael

      • Posted March 18, 2014 at 2:52 pm | Permalink

        Hey Michael you just published part two of the article! :) ah well

  8. Posted March 18, 2014 at 12:27 pm | Permalink | Reply

    Good article! I can also highly recommend “The Intelligent Gardener” book by Steve Solomon. It’s still hard going but easier to digest and understand than most soil sciency books around. I also would highly recommend Steve’s other book “Growing Vegetables South of Australia” that has helped transform my veg produce towards nutrient dense amazingness like never before!

    • Posted March 18, 2014 at 2:52 pm | Permalink | Reply

      Yep The Intelligent Gardener is listed as a resource at the bottom of the article above :) – haven’t read his other one on SA tho – thanks!

  9. Posted March 18, 2014 at 1:44 pm | Permalink | Reply

    My grandfather always had the most impressive vegetable garden. I still think his green beans were the best I’ve ever had. Understanding how to test your garden soil is integral to having a thriving vegetable garden.

  10. Nicholas
    Posted March 18, 2014 at 3:06 pm | Permalink | Reply

    Hi Michael and thanks for the detailed and informed response – hope Kirsten doesn’t mind you letting part two out of the bag early :)

    And I do agree with you about using chemical inputs to get things going – the triad of structure, nutrients and biology. Look after the biology and it will look after the other two but you need to make sure they have nutrients to immobilise first so they can then make it available to the plants. Let loose the protozoa and nematodes and get them to eat all those bacteria/fungus and spit out the unwanted nutrients for the plants.

    Cool article, impressed with your knowledge on the subject :)

    A great book on the subject is ‘Teaming with Microbes’

  11. Posted March 21, 2014 at 5:02 am | Permalink | Reply

    Thanks for these good tips. I’ve figured out how to test my soil, wasn’t sure how to reconcile the off ph levels so this is a huge help!

  12. Posted March 22, 2014 at 6:34 am | Permalink | Reply

    Reblogged this on X_trous Notes and commented:
    Take note, Syaza.

One Trackback

  1. […] I also subscribe to several websites and blogs including Milkwood and Gardenate.com. Milkwood provide very informative articles about all things permaculture and have a particularly good article on testing your soil’s pH here. […]

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