Getting to Know Garden Soil

It’s the most important thing in our gardens.  Without good soil we cannot have good gardens.  The aged and weathered soils of Australia tend to be lacking in nutrients and are often poorly textured, we can help by adding organic matter.

Organic matter is an important component of soil, which is also made up of mineral particles, water, air and living organisms.  The mineral inorganic part is derived mainly from rocks by weathering; the organic materials can be dead and decaying plants, animals and animal products.

The effects of organic matter are as follows: (Handreck, K. and Black, N. UNSW Press 1999)

  • Binds together the mineral particles improving soil structure and thereby the supply of oxygen and water to plants.
  • A source of nutrients for plants. The nutrients are released as the organic matter slowly decomposes.
  • Regulates the supply of nutrients for plants by holding them in readily available forms and reducing loss through drainage.
  • Helps to buffer soils against rapid changes in pH.
  • Helps to control root diseases, in part through a general reduction in the level of disease-causing organisms by microorganisms that are decomposing the organic matter.
  • May stimulate seed germination, root development and general plant growth through the plant hormone-like activity of some of its components.

All soils will be improved by the addition of organic matter. If you have a sticky clay soil the organic matter will improve the structure, as will mixing in some coarse river sand and spreading some gypsum.  Sandy soil needs organic matter to improve its ability to hold water and nutrients.  And if you are fortunate in already having a nice loamy soil, it needs to be maintained.

How we work our soil is also important.  Avoid digging if it’s either too wet or too dry as both will damage the structure of the soil, which includes the humus.  This is what is left after the organic matter has broken down and it gives the soil its colour. Humus retains nutrients and is essential for the well-being of soil and its ability to support plant life.  Decomposing plant matter or compost added to the soil should be considered an essential ingredient in our gardens, together with keeping up the mulch.


(References: Handreck K., Black N., UNSWP 1999 Growing Media for Ornamental Plants and Turf)