Soil is the natural material in which a plant grows. All plants are provided with the nutritional requirements from the soil, provided it is itself healthy and in good condition. The soil also provides structural support to the plants that grow within it. Plants require a soil depth of 200-300mm, if not a bit more, to gain all their nutrients and structural support required.

Within the soil, there are five different layers to a soil, which are called horizons:

• O Horizon-theis is the organic matter layer that sits on the top od the soil, being composed of things like leaf litter.
• A Horizon-this is the topsoil layer, where plant roots and soil organisms live
• B Horizon-the subsoil
• C Horizon-weathered parent material
• D Horizon-parent material (bedrock)

There are five components to healthy soil:

• Mineral/inorganic component-this is composed of particles ranging in size from large rock down to sand and particles of clay or silt that you can only see through a microscope.
• Organic matter-the remains of plants and animals thay eventually decay down to humus, which is a large source of the nutrients required by plants. The humus also has a role in resisting changes in soil acidity, improves water holding capacity against gravity (prevents too much water draining out of reach of plants), improves soil temperature, structure and aeration and, finally, has an influence on the biological, chemical and physical properties within the soil.
• Soil water-Water is held in the pore spaces of the soil. The water holds nutrients in solution, ready to be taken up by plants or it is moved through the soil by other forces like gravity.
• Soil organisms-there are the several groups of organisms living in the soil. There are the mesofauna that are large nough to burrow into the soil, the microfauna that are smaller so move through the soil pore spaces, and finally the microflora which are organisms like bacteria and fungi. We cannot forget the plant roots too. All organisms that call soil home help to break down organic matter, allowing it to be used again by plants. Without a diversity in soil oranisms, the nutrient cycle is slowed considerably or stopped altogether.
• Soil air-just like humans, plants and their roots need oxygen to respire (breath) and function correctly. As with water, air in the soil exists in the pore spaces of the soil. Without access to this air, the roots (then the whole plant) would die.

Soil texture is important as it can predict many soil characteristics that affect plant growth. The texture of a soil describes the overall soil particle size, from microscopic to visible to the naked eye. The are three main types of soil texture, as follows:

• Sandy soil-free draining but does not hold much water for plants to access when required. It is low in organic matter (meaning fewer nutrients for plants). They can be water repellent, where water is unable to soak into the soil.
• Loam soil-this soil is also relatively free draining with the ability to hold onto some water that plants can access. Loams do contain more organic matter, and therefore nutrients for plants. A crust can form on the soil surface here, which will prevent air and water from entering the soil.
• Clay soil-can be very hard to cultivate due to swinging between sticky and hard when wet or dry respectively. Clay soils are slow draining due to the small particle size, which also means that they become waterlogged easily. They do contain organic matter and supply the majority of the plants nutritional requirements.

Do take note of the fact that there can be exceptions to the general texture characteristics of any soil, no matter what texture they are. The best advice is to get out in your garden and get your hands dirty, play with the soil and, most importantly, have fun doing so! It can also be good to get out and about in your neighbourhood and observe the sort of plants that grow well, especially in your direct neighbours gardens, allowing you to better select plants that will do well in your garden.

Soil structure describes how the soil particles stick together to form aggregates, or peds, and how these peds and the spaces between them function in the landscape. The structure of the soil affects things like water movement, heat transfer and aeration within the soil. The amount of clay within the soil is the most influential variable in the formation of peds, with organic matter also being important-the higher the content of these two components, it is more likely to have a higher degree of pedality.

Soil can be pedal, where the peds can be seen-there is weak, moderate and strong pedality, with ped size varying from under two millimetres to over 500mm. Ped shape can also vary. Apedal soils have no visible peds, being either single grain (loose soil particles) or massive (large fragments).

The pedal nature of the soil structure is important:

• peds are less mobile due to their size compared to single particles, meaning the peds are less prone to wind or water erosion
• pedal soils have a range of pore spaces, both in size and distribution

A good pedal soil strucure allows the subsoil (B horizon) to provide adequate drainage deeper down into the soil, while at the soil surface there are good conditions for plant growth.

• Lauricella, J.M., Thomas, A.M.D., 2011, Horticultural Soils 1-Physical Characteristics course notes Sample Soils and Interpret Results AHCSOL401A Northern Sydney Institute TAFE NSW, delivered semester 1 2016
• Handreck, K., Black, N., 2010, Growing Media for Ornamental Plants and Turf 4th edition, University of New South Wales Press Ltd, Sydney, Australia
• Stewart, A., Leake, S., 2017, Grow Your Own How to be an Urban Farmer, Murdock Books Australia, Crows Nest, NSW, Australia
• Georgiadis, C., 2021, Costa’s World, HarperCollinsPublishers Australia Pty Limited, Sydney, NSW, Australia