Canberra Soils
                                                       (August 2016)
 
Your humble garden soil is anything but – soil is a diverse media containing a hive of microbial activity and interactions with minerals, moisture, organic matter, air and rock in various stages of decomposition. A more fascinating and scientific subject would be difficult to find. Plants rely on soil for survival and so it makes sense to conserve and improve our patch of land in order to grow the healthiest, most prolific plants we can, for both ornamental and productive uses.
 
Unimproved Canberra soils are generally clay based, deficient in organic matter and often compacted. Potentially this means fertility is reduced and soil is prone to either drying out or becoming waterlogged. It also makes it difficult for plants to grow and access the soil air and water required for healthy growth. There is a lot to love about clay though, including the fact that with the right preparation it offers an extensive range of minerals, good anchorage for plant roots, and maintains soil moisture more effectively than sandy-based soils (less watering and money spent).
 
When preparing clay soils for planting, there are a few rules to follow to avoid costly mishaps including:

• Collect sample of soil typical for the area by firstly scraping away mulch and loose organic matter then scooping out an adult handful. Dampen it with water and work it through your hand, noting if it is sticky and holds together like play dough, forms a loose clump, or is more crumbly and falls apart (if you can put Humpty Dumpty’s wall back together, then you can be quietly confident that you have a significant clay component to your soil, or, you have dug up an abandoned clay kiln perhaps?). This will give you an initial idea of the proportion of clay in your soil and what it may be like to work with.
• Put sample in jar of water, give it a shake and observe the layers it forms as it settles, how long it takes to settle, and how clear the water becomes over a day or two. Coarser particles (sand) settle at the bottom and increasingly finer particles (clay and silt) settle towards the top. This will give you an indication of the proportions of sand, silt and clay you have in your soil, and also whether it is a well structured clay (pedal) or a poor one (apedal). The water in the latter takes much longer to clear, if at all, and can be noticeably improved by the addition of gypsum. Dolomite can be used if you are also trying to raise pH levels.
• Cultivate soil with care when it is moist and neither too wet nor dry in order to preserve its structure. Make sure you only ever dig down as far as spade depth as you don’t want to penetrate subsoil and compromise drainage. You are better off raising the soil height above its original level if the topsoil layer is shallow. Adding organic matter also helps to improve drainage and add nutrients to the soil.
• Mulching clay soils is particularly important as it prevents them from becoming compacted and impervious to water. Minimising foot traffic on garden beds also prevents soil from becoming compacted.

And as for watering plants, this can vary depending on aspects such as soil type, weather, age (newer plantings need more frequent watering than established ones), and a particular specie’s drought tolerance. Plants in sandy soils require more regular watering than those in clay ones as water tends to run straight through. A simple gauge is to water if the soil feels dry more than a couple of centimetres beneath the surface.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Clay based soil with homemade compost added to improve drainage