Weekend Project
Justin Newcombe's tips on outdoor DIY projects

Weekend project: Getting the good soil

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Diagnosing any potential problems with your soil early can save you problems in the long run.

If you can make a clay pot or a bangle out of your soil, you have problems. Ideally you should be able to squeeze it into a crumbly sausage.  Photo / Steven McNicholl
If you can make a clay pot or a bangle out of your soil, you have problems. Ideally you should be able to squeeze it into a crumbly sausage. Photo / Steven McNicholl

If you want green fingers then I suggest you get brown fingers first. Chocolate-coffee brown if possible, because gardening is not about plants, it's all about soil. Testing your soil is going to save you a whole lot of emotional, physical and fiscal pain, because if you diagnose any problems from the outset, you can cure them before planting your precious flowers and vegetables. What grows on top of the ground is simply a reflection of the quality beneath it.

Most soil diagrams show three layers of strata - mulch, loam and sub-soil. The mulch layer is a composting layer which grows the soil. Loam is what most people think of when you say the word "dirt". Sub soil is what people think of when you say the word "clay".

In an ideal world we want the deep, rich crumbly loam, found in Auckland's volcanic belt. These are"formula one" soils. But most of us have heavier, sedimentary, uplifted soils best described as "demolition derby".

Test 1: The spade test

The spade test tells us how deep each layer of soil or strata is, what it consists of and how alive it is.

1. Chop a square out of the ground with your spade around 20cm deep. Take note of what's above the ground. Check for plant varieties, weeds, excess water on the surface. Is it dry? Are there cracks? Is the soil hard or soft? Does it smell?

2. Rub some between your fingers. Is it greasy or sandy or cake-like in consistency ? Trust yourself. You know when something looks bad or smells off. Think about what a plant would probably like, then look at what you've got.

Test 2: The bangle test

Remove a tennis ball size piece of soil from the spadeful you've just dug up. Mould a sausage shape an inch thick. If the soil is sandy or volcanic you may have trouble doing this. Work your sausage into a long shape. If your sausage breaks up when you move it slightly, then you have a pretty good consistency loam. The closer you get to forming a bangle the heavier your soil is .

If you are now the proud owner of a dirt bangle it's safe to say you have a heavy clay content in your loam.

Test 3: The jar test

Crumble a sample of soil as finely as possible. Place in a jar, fill with water and shake vigorously. As the sample settles, the largest, heaviest particles (usually sand) will settle first, then the loam and finally the clay, which may take up to 24 hours. This will give you a clear indication of your soil structure.

Test 4: PH test

Get a kit from Bunnings and follow the instructions. Conduct this test annually as acidity can fluctuate a lot over a year.

Where to from here?

Most soils in are a bit heavy, creating a wetter, colder, soil structure. Add gypsum and loads of organic matter and use raised beds. If your soil is too sandy then your problems will be in keeping moisture and nutrients in the ground. I recommend also adding plenty of organic material.

Remember, soil is a living, breathing organism. It has taken thousands of years to form.

One teaspoon holds more biological life forms than there are teaspoons.

As a sensitive organism, soil needs your support if you are going to use it to create a generous garden.

Compost and mulch are among its best friends.

DIY workshops at your local Bunnings warehouse this weekend:

Saturday: 10am: Craft in the garden - kids' workshop; 11am: How to make a hanging bird feeder; 1pm: How to assemble a garden shed.

Sunday: 10am: Craft in the garden - kids' workshop; 11am: How to lay stepping stones; 1pm: How to erect a sun shade.

- NZ Herald

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