Commercially made potting mixtures are relatively cheap these days. They contain a unique blend of materials for holding plant roots and carry nutrients the plant needs for growth and sustenance. The downside is they often rely on inorganic materials and synthetic fertilisers.
Home made potting mixtures can contain many different types of ingredients found around the home and garden. Some even include a base of ordinary garden loam, though I don’t recommend this.’
The ingredients you choose should allow for good water retention due to the environment if the pot especially terracotta or clay pots. The ingredients should also contain enough loose organic matter to allow nutrients to remain held in the mixture for the plants to use as needed.
Most of the ingredients you use will already be around your home but you may need to purchase one or two things:
1. Garden Compost. This should be a combination of old hay and lawn clippings. Garden compost should be well aged so it is ideal to maintain a separate compost heap you can leave alone for several months specifically for potting mix. Compost should be placed in a black plastic bag and left in the full sun for a couple of weeks to solarise and kill any remaining weed seeds. This should form the basis of a home made potting mix.
2. Draining aggregate. This may be the only thing you will have to buy. The cheapest option would be Perlite based Cat Litter available from your local supermarket. A simple no name brand will be suffice.
3. Pulverised Sheep or Rabbit Manure. This will provide an immediate nutrient source and will also act as a retention source for the addition of future Nutrients as well as a basis for the duplication of bacteria.
4. Worm Castings (Vermicast), is an ideal addition to a potting mix for conditioning, fertilising and for adding worm eggs which are contained within the vermicast. When these eggs hatch the worms will help breakdown the organic matter in the potting mix. There is an old wives tale that worms can damage a plant in a pot but this is not true.
5. Composted Wood Chips. These make an ideal addition to a potting mix. Ideally made using a home shredder, these extra-fine wood chips provide aeration and bulk as well as an additional drainage aggregate.
An equal measure of each of these ingredients should be mixed together for a standard potting mix. Variations could include a finer mix for seed raising using only vermicast with draining aggregate or a coarser mix for orchids using an extra helping of drainage aggregate and composted wood chips.