How to do a DIY Soil Test

living soil looks like this edible backyard nz

Soil is the heart and soul of your food garden.

The wellness of your soil dictates the wellness of your plants.

  • How well is your soil?
  • Is the ‘stuff’ you add to your soil improving its health?
  • Is the money/time you are spending worth it?

These key questions speed you on your way to soil greatness, which in turn speeds you on your way to garden greatness. Read on, for all the answers!

What Does Healthy Soil Look/ Feel/ Smell Like?

choose the best soil in your garden

A squidgy, moist chocolate brownie is vegie growing soil perfection – this is what you are shooting for.

  • Dark in colour.
  • Air pockets dotted throughout.
  • Worms.
  • Smells earthy and good.
  • Roots dive deep throughout.
  • A lightly moist, almost peaty texture – a chocolate brownie!

The reason we need to focus on creating this type of soil is not so much for the plants, but rather as a home for a broad range of soil life. In the same way we need a broad range of life in our gut for best health, so too plants and trees need a large team of below ground organisms to function at optimum.

Millions of microscopic life forms exist in balanced soils – protozoa, fungi, bacteria, nematodes, arthropods – performing all the checks and balances that keep plants productive and well. From accessing minerals that are in short supply to siphoning off minerals in excess, to cleaning up toxins, building immunity, sharing moisture, sharing defences against pest and disease – its astounding what’s happening beneath our feet. The more we can tap into this resource, the easier our garden life. We do this, by staying in touch with our soil.

“… the tiny animals that live below the surface of a healthy pasture weigh more than the cows grazing above it. … two handfuls of healthy soil contain more living organisms than there are people on earth. What these beings are and what they can be doing is difficult to even begin to comprehend, but it helps to realize that even though they are many, they work as one”

Carol Williams, Bringing a garden to life

When to test

There are 2 tests I’m keen to get you doing. A quick mini one before planting each crop – best habit of your gardening life. And an annual one, that’s takes a little more time but will show you on a deeper level how your garden is responding to the inputs you are using.

An annual test

Test your soil when you are new to a garden. Note your findings on your basemap. These observations will help you choose where to put gardens, trees etc, and will give you a baseline comparison for the years ahead.

There after do this test at about the same time each year in roughly the same spots. Choose a few about the place – its startling how different soil can be from one corner of your property to the next. I do my annual check in November or December before soils dry out in the vegie patch, berryhouse, greenhouse, orchard and paddocks.

Dig up a square of soil that’s a spade by spade wide and a spade deep. Lay it on a bit of cardboard (or some such) then right away count the worms before they wriggle away.

In an ideal world you’d have close to 30. Egads, you may be thinking after only counting 2. Never mind. You’ll get there. My first ever worm count revealed – 0. Not a sausage. 9 years later – 20. 9 years! Dont worry, it wont take you that long, because you’ve got all my hard learned tricks up your sleeve.

sniff the soil

Grab a handful and take a sniff. Smell tells you alot. Sour or musty and you’ve a distinct absence of life. Earthy and good, guaranteed you’ve got a vibrant soil life going on.

Squeeze a handful, then open your hand out. Good growing soil will loosely stick together in a few clumps with a few crumbs that fall away. Poor growing soil will either slip through your fingers with nothing much sticking together or will stay moulded, retaining the shape of your fingers.

Should your soil not be ideal, perhaps don’t push it. Rather grow in pots and containers while you attend to your soil and get it up to scratch.

Dive deeper into soil building in my book “The Edible Backyard”. I wrote this just for you, for exactly this moment, to answer all the how to’s that bring you to an easy to work, highly productive, nothing much to buy in food garden.

Make a Record

Note the worm count, the texture, the smell and take photos of both the clod of soil you dig out and the hole it came from. That way you can compare the subtle changes, year on year. Slowly, slowly the wheel turns and on the back of these soil improvements, above ground changes occur – less pests, less disease, different weeds, better harvests.

If nothing changes, then you have the opportunity to rethink how you are treating your soil.

A Mini Soil Test Before Each Crop

perfect beetroot sowing soil - friable and lush

Use a much simpler version of this test every time you put a new crop in the vegie patch. Simply scoop out a handful and smell, feel, worm count – get a mini low down. This regular check in keeps your finger on the pulse of your vegie patch.

Sometimes, based on this assessment I change my mind about where I’m planting something. If for instance, the soils a bit dry and musty instead of planting hungry squash, I’ll find another, healthier spot in the garden to use and greencrop the musty spot instead.

A Lab Test for Soil Life

If you want to accelerate your soil health journey with a lab test rather than your own DIY job, get the total bacteria/ fungi report from the Soil Food Web lab. Test for the life because they are the lynch pin for ph and mineral balance. After the test, Phil will helpfully run you through what you need do to restore absent life and get your patch humming again.

Whether you jump in and do this right from the get go or have a play with following your intuition and trying DIY for the first while, really is over to you. Either way you’ll learn heaps and at any stage can change it up.

A Lab Test for Contaminants

Here’s a free test I recommend all my customers. Send a soil sample away to Soil Safe NZ to check for heavy metals/ contaminants. You never know what went on before you got there – lead paint, buried rubbish, residue from burned rubbish, fuel spills, pesticides, treated timber – they all stick around and turn up in fruits and vegetables. Its peace of mind to know that the area you grow your food in is safe.

Recommended Reading

“For the Love of Soil” by kiwi legend Nicole Masters, is well worth a read if you are keen to learn about the thrilling complexity that is unfolding below, what the weeds are telling you about your soil and all you need understand about creating chocolate brownie, as she coined it. You’ll see soil in a whole new light.


  1. Susan McCardle says

    Hi Kath, I made the mistake of putting torn foxglove leaves into my veggie patch when I was planting new seedlings thinking that it was comfrey.
    Would you know if I have made the soil toxic now from doing this?
    Many thanks