Three ways to test your soil and ensure successful vegetable growing

There are three simple tests you can do a home to find out more about your garden and increase your chances of successfully growing food.  These tests can be done anytime but tests 2 and 3 are great winter jobs as you have time to make changes before the spring and summer growing season.

Test number 1: temperature


A simple soil thermometer is a helpful tool to have in your garden kit if you, like me, grow vegetables. You will find many guides to growing vegetables will give you a temperature range to follow for each plant.  Soil thermometers are easy to find at garden centres or hardware stores. Insert the thermometer well down into the soil. You want it to measure the soil temperature not the air. Its winter here, 12 degrees Celsius in the air, 10 degrees in the soil.

Test number 2: soil type


Do you know what type of soil you have? The soil in Robertson is a lovely rich red and friable. Over the years I have added lots of compost and mulch to my beds and the soil has loosed up.  But how do I know if its clay or a sandy loam?

Take a clean, clear glass jar and fill with water to approximately the 3/4 mark. Take a handfull of dry soil and add to the jar. Shake well to break up any lumps.  Set aside to settle, this might take 10 minutes or so.  When completely settled have a look at the layers that have formed in your jar. Any soil that has settled to the bottom is sand, soil floating at the top is clay. The middle is silt. Which layer is the biggest? That's your soil type.

If you have a high proportion of clay you can break it up by adding gypsum.

Test number 3: soil pH


The pH of your soil is very important, especially for growing vegetables. You can buy a simple testing kit from a garden centre or hardware store. The one I have can be used many times. Your kit should come with easy to follow instructions. Essentially you mix a little of your soil with barium sulphate, the test solution and water.  The mix in your test tube will turn green or orange/red.  Compare the colour against the chart in your kit to find out if your soil is alkaline (green) or acidic (orange/red).  Now you know your soil pH. My booklet has a comprehensive list of the preferred pH for flowers, vegetables and fruit trees" they can vary a lot in preference.

The rule of thumb is that most vegetables prefer an acidic soil between 5.5 and 6.5 pH. Most nutrients can be absorbed at this level.  Now that you know your soil's pH you can either choose plants that suit or change your pH levels. Acidic soils have a low pH which can be raised by adding lime. Alkaline soils have a high pH which can be decreased by adding sulphur. How much you add depends on your soil type and how many points you want to raise or lower the pH. Formulas are easy to find so I'm not going to repeat them here.

Here's a tip that might help you test your vegetable garden effectively. Take an egg carton and mark out by number or description each garden bed on the inside of the lid. You should be able to just make that out in the photo above.  Dig a hole in each garden bed and take a soil sample from 10-15cms down. This should be truer to type that near the top where you will have a mix of mulch and potting mix from seedlings. Your soil needs to be dry before you test it so set your carton aside for a few days, taking care not to tip it and mix your samples.  When you run your test you can take a small sample from a specific bed, test it, record your results, wash out your test tube and move on to the next sample.

I made some interesting discoveries: the soil in my potato beds is completely natural for this area, as in no compost, and tested at 6.5pH. The soil in my other beds has been topped up with compost and tested between 7 and 7.5pH, far too alkaline for vegetables.  I worked out why: my compost had too much wood ash in it. I need to add a whole lot more manure to the compost and add some sulphur to the beds. I will add a little to the potato beds too as I suspect the soil may be a little depleted there anyway. I am glad I tested now so I can adjust the levels before the main planting season comes on.

So there you go, testing your soil is simple. I hope my explanations take out some of the mystique and help you feel confident to do it yourself. Happy gardening.