Soil… most people just think of it as dirt, something to grow a few plants in, and maybe something to play in when you are young. However, (healthy) soil is a living, breathing organism, vital for the health and well-being of our precious plants out in the garden. And just as we feed and nurture our plants, so must we feed and nurture our soils. But what determines a healthy soil, how do we achieve it, and how will it benefit us as gardeners?
What is a healthy soil?
Firstly, lets’ talk about what soil actually is. Technically, it is the thin layer of material that covers the earths crust, providing plants with support, mineral nutrients, water and air.
Soil is derived from the weathering and breaking down of parent material (rocks), with the addition of varying types and levels of organic matter supplied by the break down and decomposition of plant and animal material. The amount and type of organic matter in the soil, coupled with the original parent material, determines the structure, nutrient content and behaviour of the soil. All very important factors to understand when planting out a garden.
Most Australian gardeners are presented with quite poor soils as a result of housing and urban development, overworking, previous chemical practices, poor watering practices and so on. But, as we know, the most important factor in a healthy garden is healthy soil. This basically means that your plants can only be as good as the soil they grow in. If you have an exhausted soil with no nutrients your plants will struggle and may starve to death. If you have light sandy soil your plants may not get enough moisture and will probably die of thirst. If you have heavy clay soil your plants will not get enough drainage and will probably drown!
Good soil is full of life, and it needs some of the same things which animals and plants need to survive… like air, water and nutrients. We can not easily see all the activity going in the soil but we can smell it and feel it to get a sense of its health. Healthy soil smells sweet. It’s loose, well drained and rich in organic matter. Air and water move freely through the soil because air space exists around soil.
Healthy soil will have about:
- 24% air
- 25% water
- 45% minerals
- 3 – 5% humus (the dark organic material that is the end product of composting)
- up to 1% living organisms
But what if your soil is not healthy and your plants are not performing? Fear not, we have the answer!
How can I make my soil healthier?
To have lovely healthy plants, you need healthy soil, and to have healthy soil you need the following important ingredients:
- Good drainage
All types of soil benefit from the addition of compost, as the presence of organic material in the soil introduces microbes and worms which break down the compost. And as we all know, worms are the gardener’s best friend! They are so industrious in decomposing dead and decaying organic material that in a short period of time their activity can greatly improve any soil type. Worms are not limited to just decomposing organic material, they greatly increase the microbial activity within the soil, mix and aggregate the soil, provide paths for fine roots to grow along, and increase both water filtration and water holding capacity.
The water retention in light, sandy soil can be greatly increased with the addition of organic materials and bentonite clay. This in turn creates an ideal environment in which the worms will thrive. As the compost breaks down nutrients are released into the soil, also creating a food source for your plants. So this simple process dramatically improves light soil in two very important ways, providing a long term remedy to these problems.
Even heavy clay can be greatly improved by the addition of compost. Don’t break your back trying to dig up heavy clay. Just add a generous layer of compost on top of the soil, cover with lots of lucerne, pea straw, or fine mulch, and then go and do something else in your garden! Give the area an occasional watering during hot weather, otherwise leave it to the rain to keep the area moist. After a few months you will find an enormous amount of worm activity has taken place, which will have broken up the clay, improved the texture of the soil, and subsequently improved the drainage too.
Producing your own compost is really easy. For further information on making your own compost, check out this post.
Other materials that can be incorporated into the composting process include animal manures, which will introduce valuable microbes into your compost ‘micro climate’. Indeed it is much wiser to use these in your compost recipe, so that by the time you apply the compost to your garden the manure is well rotted. Fresh manure should never be applied directly around plants, as it will burn the roots and severely stress your plants. One very important thing to remember is to avoid obtaining horse manure from racing stables, because if the horses have been treated with antibiotics and worming treatments then the manure will not contain the desirable microbes needed for healthy composting. This can even result in the subsequent death of your plants as there are no ‘good’ microbes in the soil! Make a point of getting your aged manures from only natural, organic sources.
Worm farms are also an excellent idea, offering a convenient alternative to compost bins if you don’t have much space in your garden. This is another way to provide your garden with important nutrients and organic materials, and a very easy way to ensure you have plenty of worm activity to help improve your soil quality.
Moisture and Mulch
It’s almost impossible not to mention these two topics in the same breath! A great deal has already been written about both, but it is still worth remembering that mulch is the most effective way to keep moisture in your soil. You can choose from a wide range of mulch materials, but remember that it is very important to apply a generous deep layer of mulch. Don’t be tempted to spread it too thin. If your garden provides you with lots of prunings throughout the year, invest in a shredder and make your own supply of mulch to add to your garden – the ultimate in garden recycling! Mulching also acts to suppress weeds, keep soil temperature stable and stimulate microbial activity, meaning less work for gardeners. Mulching should be considered an on-going soil conditioning process, and is as essential in the garden as pruning and weeding.
Hydrophobic soils are soils which have dried out and become water repellent to the point where water beads up and runs off the surface. Water is no longer retained in the soil and plants become highly water stressed. It will occur more easily in sandy soils and in soils with high organic content. The best way to fix this problem is to use a soil wetting agent (not water storing granules – they are a different product for a different purpose). This will often need to be applied more than once, and once the soil appears to be wetting correctly, give it a good deep soak and do not let it dry out again. If possible add in highly composted organic matter, either dug in or as a mulch. This will aid microbial activity and that too is beneficial to soil health.
Whatever your soil type, good drainage is essential for healthy plants. Of course, if you have light sandy soil, the drainage is probably too good! This is where the use of compost will greatly reduce rapid moisture loss, and improve the soil’s capacity to retain water, which is really important in these times of water restrictions. Heavy soils also benefit from this process, but some gardens may need more work than others! If you have a brand new house and a bare block of land which only offers compacted clay and subsoil, don’t lose heart; compost can help!
Don’t be tempted to plant straight into compacted clay, as very few plants are tough enough to handle it. Compacted fine clay particles don’t allow water to drain away, so winter rains will cause the roots of plants to rot, and the hot summer sun bakes the clay as hard as concrete! Adding compost and mulching will help improve this soil, allowing water retention and drainage as the organic matter breaks down and mixes with the heavy clay soils.
In addition to a composting and mulching routine, some people opt to import new topsoil into their gardens. The best type of topsoil is a dark sandy loam, rich in organic matter to hold moisture but with enough coarse particles to allow good drainage. So if you need to buy topsoil, this is a very good investment. An important tip when establishing new garden beds is to avoid compaction of the topsoil before planting, although it is important to rake the soil evenly to ensure removal of air pockets. The soil will settle naturally, especially after watering, so you may even find it necessary to ‘top up’ the levels with extra soil after a few days.
Don’t forget to add compost to the soil regularly to encourage lots of worm activity and guarantee excellent drainage!
But why is this so important?
Under the current climatic (and political) conditions, it is unlikely we will ever live in a time without water restrictions again. And why should we? By developing water wise gardens and adopting water capture and re-use behaviours such as rainwater and greywater usage, the need to irrigate our gardens with drinking quality water is a thing of the past. While plant choice and groupings, environmental conditions and garden micro-climates are all important aspects of a water sensitive garden, a healthy soil is the most important feature of a sustainable, water wise garden.
Healthy soils with high organic matter content require less water, little to no additional fertiliser and are less likely to change structure and performance during long-term irrigation with greywater. Plants in healthy soils will be more vigorous, robust, and less prone to attack from pests and diseases, saving gardeners time and money. In turn, the environment is spared the damaging affects of prolonged fertiliser and pesticide usage… a great result for us, and future generations.
VegeSafe – Affordable soil testing
VegeSafe is a community science participation program run by Environmental Science staff at Macquarie University, the only service of this kind in Australia. Their aim is to inform the community about metal and metalloid contaminants in their garden soil through their soil metal testing program. Participants receive a formal report with their soil results and are provided with links to information and advice about what to do next in the event of soils containing elevated concentrations of metals and metalloids. They accept soil from all Australian states and territories, but do not accept soils from overseas due to Australian quarantine regulations.
You will need to fill out a consent form and mail the sample in a ziplock bag. They also request that you send a $20 donation with the sample… this is such a fantastic service that we would encourage you to send more if you can afford it!
All the info you need to get started can be found at https://research.science.mq.edu.au/vegesafe/