The water restrictions in the Western Cape are especially harsh on gardeners with a poor quality soil. It must be very frustrating when you water your garden on the specified day per week, but realize that the water doesn’t filtrate very easily into clay soil, or does so far too quickly, thereby leaving your sandy soil dry again all too soon.

A healthy soil is a medium that plant roots can thrive in, and from which plant growth can be sustained. It is made up of mineral particles (clay and sand) (45%), organic material (5%), water (25%), and air (25%). The correct ratios between the four components are crucial to ensure porosity and therefore the balance of water and air in soil.

A high level of clay, i.e. fine particles, in the soil means that even if only a thin crust on the soil surface becomes compacted, it will dramatically increase the amount of runoff and precipitation. The addition of compost will help more water filtrate into the soil, and therefore increase the water available to the plant roots.

Compost added to sandy soils will improve the water holding capacity of the soil. The organic matter in compost is able to absorb water, and so prevent it from filtering straight through the sandy medium. It is then available to the plant roots for a longer period of time, thereby reducing the amount of water used in the garden.

The water holding capacity of soil, especially that available to the plant roots, is important in the entire garden, more so during a drought, because as a plant uses the water closest to its roots, that soil dries, and in response, water from wetter areas moves in. And secondly, if the soil is more porous, the roots are able to grow more widely and therefore have greater access to available water.

Air is essential in soil. Most plants and soil microorganisms require oxygen for respiration, and as a result release carbon dioxide. The most common means of replenishing oxygen and removing carbon dioxide from the soil is through diffusion. Diffusion is the movement of gasses from a higher concentration to a lower concentration. The atmosphere has a much higher concentration of oxygen, but to diffuse into the soil, there need to be air pockets available. The use of compost will ensure your soil never becomes too compacted for the necessary air movement.

Compost is not only needed in the soil, but can also be very beneficial on the soil surface as a mulch. A thick layer of coarse, well composted material will work best, but a 3 – 5 cm layer will be sufficient to ensure that it will: