SINGAPORE – Many gardeners use basic potting soil to grow plants in flowerpots and troughs indoors.

The disadvantage of this is that, with time, this soil-based growing medium compacts and becomes a heavy mass. This is due to the breakdown – and subsequent lack – of organic matter, coupled with the settlement and aggregation of the soil’s heavier clay component.

Gardeners who use potting soil will have to regularly fork in compost to keep the soil porous for proper aeration and drainage. This needs to be done carefully to avoid damaging roots. 

Enter potting mixes – man-made growing media designed for container gardening. Many home gardeners buy and use such mixes without knowing that some of them contain no soil.

These are called “soil-less growing media”, and are much lighter than a similar volume of actual soil. Soil-less media are designed to stay fluffy and porous with use, thereby overcoming the issue of compaction that is typically associated with potting soil. 

The bulk of soil-less growing media consists of an organic component, usually peat moss or coconut coir. Less common materials are compost and burnt rice husks.

Such organic materials have a fine particle size, which makes for small pores and a mix with moisture-retentive properties.

Peat moss is acidic, and retains nutrients and moisture well. However, it is gradually being phased out due to sustainability issues, as harvesting it involves disruption to natural habitats. 

Finely chopped coconut coir, also known as cocopeat, is widely available in this part of the world. It is an upcycled plant waste material that is often used to replace peat moss.

On the flip side, unwashed or poorly washed cocopeat may have high salt content, which can be harmful to plants. This material needs to be soaked in water for several rounds to lower the salt content if you want to use it to make your own potting mix.