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Heavy, clay-based soils are hard work. They’re difficult to dig and even if you manage to break through and dig a hole or trench for planting, it’s not the ideal growing environment for most plants. Clay holds onto nutrients and water well, but too much clay leads to drainage issues; in the long run, plants are unlikely to survive.
The good news is that you can improve the soil, but it is not an overnight fix. The addition of soil conditioners and amendments like organic matter and gypsum will help to break up the clay and improve the overall soil structure.
How do you know if you have clay soil? Aside from being difficult to dig, when wet, clay is sticky, pliable and takes a long time to dry out. Medium to heavy clay soils will take a long time to drain, too. If this is the case for your soil, you will need to improve the soil prior to planting.
Before taking action, try doing a simple test to see what additives will be beneficial for your soil. Take a small sample of dry soil and add it to a jar of clean water. Do not shake it, but simply observe. If the water becomes milky and cloudy, the soil will respond well to the addition of gypsum, a well-known clay breaker. If it’s not cloudy, it’s unlikely gypsum will help.
Apply organic matter like compost, blood and bone, and aged manures liberally to the area. Add gypsum if needed, following the instructions on the back of the pack to understand how much is needed. Gypsum is available in both powdered or liquid form, with the liquid being more fast-acting than powder. Dig all the additives well into the soil. Repeat applications may be required to further loosen the soil.
If the soil is too difficult to dig, layer compost and manures over the area and cover with an organic mulch like sugar cane or pea straw. Wet the mulch and allow it to break down over the next few weeks. If it’s workable, dig it all in, but if not, allow the organic matter to further break down.
To check if plants are ready for planting, dig a hole at least 40cm deep, fill with water and note how long it takes to drain. If the water drains away after a couple of hours, it’s moderately well-drained. However, if it’s still sitting there after a day, you have more work to do.
Once plants are in, it’s ideal to continue to add organic matter and gypsum 2–3 times throughout the year. A healthy soil ensures plants are happy and less prone to pests and diseases.
There are plants that are more tolerant of growing in clay soils, provided they’re well-drained. In fact, once established, they will thrive too.
Follow our guide to testing and adjusting your soil pH, essential to growing healthy plants.
Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page.
When following our advice in our D.I.Y. videos, make sure you use all equipment, including PPE, safely by following the manufacturer’s instructions. Check that the equipment is suitable for the task and that PPE fits properly. If you are unsure, hire an expert to do the job or talk to a Bunnings Team Member.
