Seedlings need a mix that holds water but still lets air reach young roots. Peat Mix blends sifted mature compost with low-salt fibre and an air-space material such as pumice or perlite, balanced to a seedling-friendly pH and a low salt level. It is steam-pasteurised before beneficial Trichoderma and Bacillus microbes are added, so you can fill your trays straight from the bag. It is built for propagation cell trays, not for field planting or large pots.