To make your own seed raising mix, mix together equal parts of coir and coarse washed sand.
You can also add perlite/vermiculite and some seived worm castings if you have them but although beneficial, neither are necessary.

Coir is coconut fibre which has been finely shredded and is a totally renewable resource replacing peat moss. It is often available as a 'brick' to which you add water and it expands. It's about $2 a brick and expands to make about 2 gallons.

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The secret is the soil.