Episode: WA Garden Gurus Special - Summer Gardens
Presenter: Sue McDougall

Perth is famous for its sandy soils and it is not until you move up the scarp and into the Darling Range area that the soil profile changes greatly. Any loamy soil areas are usually very shallow and are often over a laterite or clay sub soil. Many areas are so rocky that you have to pick the spots to plant anything between rocks or invest in some dynamite

The other soil type is clay and it is so hard in summer, that it is impossible to dig a hole with out the use of a crowbar and in winter it becomes really sticky.

Clay particles are very fine, hold more water than sand and are electromagnetically charged, which means clay molecules attract water molecules like a magnet. Making it very difficult for plants roots to break up the clay and grow through it. So even though the clay is wet, this moisture is not available to the plant and it can cause plants roots to rot.

Clay soils have no structure as they stick together and basically turn into mud when there is some moisture around. The way to improve this soil type is with lots of organic matter dug around plants roots like this organic soil mix and with the addition of gypsum.

Gypsum is a powdery natural mineral that attracts the particles of clay and improves the texture and structure making it more crumbly and improve drainage, making gardening much easier.

Not all clay soils will respond to gypsum and to find out if your clay soil will place a little in a jar of water and shake it up. If the water stays clear, applying gypsum is going to be a waste of time.

If the water doesn?t go clear, in 5 or 10 minutes it will respond to the application of gypsum. You can then add some gypsum to see if the fine clay particles flocculate or clump together.

On new soil apply at the rate of about 200grams per square metre and dig it in. Make it a good practice when you plant anything that you throw a couple of handfuls each of Gypsum in the bottom of the hole and mix in.

The other interesting point about clay soil is what we call the wetting pattern. In sandy soils the water leaches straight through past the plants roots very quickly, but in clay soils the wetting pattern tends to go out wide, so the moisture is available to all the fine feeder roots of the plant.

It is the perfect soil for the dripper style reticulation system, so armed with this knowledge, clay soil isn?t so daunting.

Richgro Gypsum Clay Breaker

• Helps to soften hard clay soils and improves soil structure.
• Great for garden beds and potted plants.