It is valuable to distinguish between tropical and temperate plant species when starting seeds. Tropical seeds without hard seed coats, don’t usually require preparation and must be sown shortly after collecting them from a plant/fruit. Hard-seeded tropical seeds require scar-ification for immediate germination (otherwise some species could take years). Scarification may be done by hand for small amounts (serrated knife/sandpaper), or with hot water (70C) for bulk amounts of seed.
Temperate seeds usually require or germination rates will benefit from cold stratification (winter conditions).
COLD STRATIFICATION: The most important preperation for non-tropical, cooler climate species is winter stratification (moist and cold, ‘winter’ conditions). Which can be done in a refridgerator or naturally outside during the winter. So when planting bulk amounts of tree seed it is best to broadcast in late fall and early winter. Most temperate climate tree species require at least 30 – 60 days of cold stratification.
WARM STRATIFICATION: very rarely do plant species require warm stratification, although sometimes it is necessary for some species to receive warm/hot conditions before the cold stratification. Sometimes found with arid/semi-arid palm species and a few other hot-climate plant species.
SCARIFICATION (scar-ification): some plant species require scarification for immediate germination, others will benefit if you scratch through the very outer shell of the seed to allow moisture to activate the germplasm. For example, citrus and apple do not require or benefit from scarification. Where as, olive and carob require scarification for immediate germination, and things like stone fruit and a lot of palm species dont necessarily require scarification, but usually benefit.