The perfect soil

Soil is a heterogeneous mix of water, minerals and

anorganic particles (by size)

• Rocks break down and wash away very slowly, improve drainage and aeration, disturb the growth of root vegetables

• Sand breaks down very slowly and wash away slowly, improves drainage and aeration

• Silt breaks down slowly washes away and is blown away by wind easily, fair to good drainage and aeration

• Clay microscopical particles in suspension, sticky, bad drainage and aeration, nutrient rich

organic matter

• Decomposing material dead plant and animal matter, manures

• Living organic matter soil bacteria and fungi, worms, nematodes and other soil dwelling animals

Textures of soil

According to it’s composition a soil is classified as ‘sandy’, ‘loamy’ or ‘clayey’.

• Sandy soil shows great aeration and drainage, dries out quickly, it’s often poor because it doesn’t keep nutrients well and doesn’t break down easily to offer new nutrients

• Loamy soil shows good balance between aeration and drainage, has good water retention, keeps nutrients and breaks down into nutrients.

• Clayey soil is heavy, doesn’t drain well, plants get waterlogged, nutrient rich

The squeeze test, how to determine soil texture

Take a handful of soil from your garden (moist but not wet), give it a firm squeeze and check the resulting bolus. Also try to roll it between two hands to form a ribbon.

no coherence, no ribbon, grains stick to your fingers

Excerpt from Plant growing media workbook

Testing drainage, the percolation test

Dig a hole 15 cm square, 30 cm deep. Fill the hole with water and let it drain completely, then fill it with water again. If it takes longer than four hours to drain, drainage is poor.

Organic matter in the soil

The content of organic matter in the soil strongly changes the soils properties.It improves aeration, has an effect on soil acidity, improves drainage and water retention, keeps nutrients in the soil offers the necessary environment for soil bacteria and fungi that plants need to grow in symbiosis with.The layer of undecomposed and decomposed organic material on the soil is called the humus layer, it is this layer and the next 5 cm of soil, where the maximum of biological activity and leaching of nutrients can be found. In the next 20 cm we find the maximum of chemical accumulation.In a natural environment organic matter is constantly fed back to the soil by dying plants and animals that decompose and become compost. In our gardens we take produce out of the system and need to ‘pay’ organic matter back. We can do this by adding

• compost
• grass clippings
• leaf litter
• mulch
• worm castings and -juice
• coconut coir

• small amounts of ash

• rotten mushroom compost and well rotten cow or sheep manure is also great, but be aware that this is also a nitrogen rich fertiliser, so don’t go over the top with this

Testing biological activity, the worm test

Dig out a 30 cm cubed volume of soil and count the worms in this soil. Worms are a good indicator of the overall biological activity of the soil. You should find about 10 worms in this amount of soil. Less than 10 worms indicate a lack of organic matter in the soil.

The most fertile soil

The most fertile soil in the world is called loess. Loess shows a loamy texture and is composed of about 20% clay, and 40% each of sand and silt intermixed with some chalk. Only 10% of the earth’s surface is covered with loess. But even loess is only really fertile if covered in a thick humus layer.