Seed need five basic things in order to break dormancy and germinate: moisture, air, heat, light (or no light), and, of course, time.  Dormancy is natural in all seed as this protects them from germinating at the wrong time of year.  Just keep in mind that you have to work in tandem with the seed as too much or too little air, water, or heat can kill embryos.  Seed packages kept out in a warm environment speeds up the embryo’s metabolism, wasting precious energy needed for germination.  Cut off the air by having the growing medium too wet can cause the seed to rot, too little water causes the vulnerable seedling to dry out and die.  Sowing deeply can restrict air to the seed killing the embryo too, so a balance of heat, moisture and air is essential.  Of course different plants need different balances of air, heat and moisture or every seed of every genus would germinate given the same growing conditions.  What sort of challenge would that be? Breaking dormancy can be rather complex for some genus as some need alternate cycles of cold and warmth to trigger germination, but this usually occurs in long lived perennial, shrub and tree species (rarely in annuals).  Another means of triggering germination involves the removal of germination inhibitors built right into the seed coat; the embryo will not wake until the inhibitors are leached away in water, juice, or dilute ethanol such as in the Passiflora genus and many desert wildflowers which will only germinate after a good ground soaking rain.  Other genus, such as Panax (ginseng), must be sown fresh because the embryos are immature when they fell from the mother plant.  They must ripen for 18 months before it is developed enough to emerge from the seed coat (all the while the seed must be kept in moist sand as a dry ginseng seed is a dead ginseng seed).  Again the germination medium must not dry out or the emergence of your seedlings will become erratic, sparse, or worse, not at all.  This use of time, cold and warm cycles in moist medium is called ‘Stratification’. The different reproductive strategies in plants are vast.  Strategies even vary within a genus.  All I know is that we know what we grow.  Please don’t ask me about fibrous begonias, dahlias, or petunias.  We start all of our seed in pots.  This enables us to have better control over the growing conditions be it environment or pests.  Having happy thriving seedlings in a greenhouse can provide a jump start to the growing season and provide an opportunity to become established faster.  I don’t usually promote any commercial products, but one we use quite often when soaking seed is called ‘Skookum Grow’, an algae extract full of natural gibberellins, auxins and other natural germination promoters.  It increased our germination rates dramatically.  Soak seed for 12 to 48 hours (depending on species and seed moisture content) until the seed swells and sinks.  Meanwhile prepare labels and seeding pots/containers.  One or two gallon sized pots are partially filled with soil less medium mostly of peat and humus amended with sand, grit and mineral fertilizers such as green sand, granite dust and langbeinite.   Never, ever use chemical fertilizers as this burns tender roots and cause seedling death.  A layer of sand no more than 2 cm (less for smaller seed) is put down, deposit seed and gently tamp.  If the seed needs covering of a certain depth, use sand, gently tamped again then apply a layer of mulch in the form of composted bark, peat, grit or a combination depending on how sharply draining the seed needs to be.  The drainage needed by Arbutus is vastly different than Gunnera.  Some seed needs light to destroy the germination inhibitors so just tamp seed into medium surface.  A plastic cover keeps in vital moisture.  Bottom heat, if needed, is provided by plug-in propagating mats.  In the dark days of winter and early spring, florescent light bulbs on a timer are used.  A warm white bulb with a cold white bulb is sufficient to provide all the wavelengths of light needed for proper growth.  Nothing is easier than to move pots when slugs, birds and varmits threaten rather than standing vigil over the seed bed.  Having rutting deer trample your peony seedling bed is near heartbreaking. When all is done and said, your happy early sown seedlings will give you larger plants at the end of summer and able to withstand the perils of winter better.  Annuals such as tomatoes started early in the spring can provide bountiful harvests whereas the same plants started weeks later, may only provide enough for a sandwich.  It’s all the mater of timing and growing conditions in the seedling’s early life.    

Enjoy.