This is what we do, and we germinate virtually everything. We sow almost everything in sunshine mix, which we mix with pearlite, one part sunshine to two parts pearlite. We fill flats in advance and water before we sow the seeds. All seed is sown directly on the surface and covered with a layer of chick starter grit; this goes a long way to prevent damping off problems. Sow on the surface and cover to several times the thickness of the seed with fine chick grit; very fine seed pots should be gritted first and the seed should be sown on top of the grit and watered down into it. Keep moist but do not over water. Fungicides are no substitute for good culture and in general, it is best to avoid them. We rarely have damp off problems and do not routinely spray fungicides to prevent it. Chick grit and care in watering is the best prevention. Be sure to use a thick enough layer to inhibit moss growth.
Difficult species are almost always best in a minimally heated white, not clear, poly-covered greenhouse. Easy species can be done under clear poly or fluorescent lights. White poly-covered cold frames should work well on a small scale; or better still, build a small Nearing Frame. Seeds that need multiple 40-70 cycles are best placed in the refrigerator vegetable drawer in a Ziploc bag with sunshine mix. This works better than baggies and towel for most species. We routinely extend the cycle time on the species Norm Deno lists as multicycle germinators. This is very helpful. DO NOT PLACE SEEDS IN A HOUSEHOLD FREEZER -- THIS CAN BE FATAL. Freezing is seldom necessary or helpful; it will crack seed coats, but there are better ways to do it. Freezing in household freezers is much too abrupt and may rupture membranes, killing the seed. If you must freeze, place seed in a coldframe outdoors in the fall. Seed can be stored in the freezer for extended periods, but only if the moisture content is very low. In general, this is not recommended. Remember for many species extended dry storage is actually beneficial with old seed germinating much better than fresh seed.
Seeds requiring GA3 can either be placed on coffee filters soaked in the appropriate concentration of GA3 (1,000 ppm is a good place to start) and the seedlings pricked off as the radicle emerges, or sown in flats and misted with a one-time application. You can also soak larger seeds until they swell and then sow out. Keep concentrations as low as possible to reduce stretch problems. We fertilize young seedling with a soluble balanced fertilizer at every watering (250 ppm total nitrogen) which is higher than generally recommended but the plants thrive on it. No burn problems at all. With a bit more fertilizer, most plants will be more likely to out-compete the mosses, which generally dislike high fertility media.
Water until runoff and let flats dry out between watering. Beware of high pH in the water. We killed a ton of stuff due to this. We now adjust our water pH to 5.6-6.0 by injecting battery acid directly into the irrigation water along with the fertilizer. Buy a portable pH pen; its well worth the investment. PH induced iron chlorosis is an insidious problem. Plants weakened by it quickly fall victim to fungus gnats and aphids. Algae and fungus gnat problems are also less severe if flats are allowed to dry out a bit; it's a very fine line. Properly dry flats will be flattened when you water but show little sign of wilting before the water hits them, and will recover quickly with no tip burn.
Be patient. There are many formulas for success, but the most important ingredient is patience. The only thing to do with some species is to sow and wait for a couple of years. Many seeds will germinate immediately with the majority coming up a year or more later. Often the early germinators turn out to be the weakest plants. We often weed out the early stragglers to wait for the main flush of germination. Don't throw away seed pots for at least four years on the long germinators. Before you trash a pot, dig around and find a seed and cut it in half, if it hasn't rotted it will germinate eventually. Don't let your seed pots dry to dust, and don't let them get soggy and moss covered. If they do, carefully cut off the moss layer leaving the seed behind and re-grit and wait some more. If in doubt about what to do, think about what would happen in nature and try to emulate it. This is a great help in determining whether to start cold or warm.
Light requirements: Most seeds have a light requirement that prevents them from germinating when buried too deeply in the ground. Sowing on top of the soil surface and covering with a thin layer of chick grit that transmits some light meets this requirement. There are very few seeds with a dark requirement. Assume everything needs light unless you specifically know otherwise. Don't kill shade lovers by placing in full sun. Be careful of high light levels; even sun-tolerant plants may be sensitive as seedlings and it's easy to crispy the little ones.
Dry storage requirements: Many seeds have a dry storage requirement that prevents them from germinating prematurely while they are still attached to the parent plant. Indeed many seeds will not germinate at all if sown too fresh. Some seeds germinate best after several years of dry storage. Do not fall into the neophyte trap of insisting of fresh seed only. About 1/2 of the seeds we sell have dry storage requirements including Composites, Crucifers, Campanulas, Penstemons and Grasses.
Warm germinators: These seeds usually germinate after a period of time at around 70°F. Most are easy to do under lights or in a warm greenhouse. In general, they are quick to germinate, but a few species with hard seed coats may need scarification or extended time at 70 for bacteria to break down the seed coat.
Cold germinators: These seeds germinate after a period of time at around 40F. In general, this is a slow process that takes from 1-6 mo.
Warm then cold germinators: These are usually seeds of plants that bloom early in the season. The ripe seeds are exposed to a period from 1 to 3 months warm at 70 or so followed by a period of 1 to 6 months at 40 F. Germination occurs during the cold cycle.
Warm then cold then warm germinators: As above, but these require a shift back to 70F before germination will occur.
Cold then warm germinators: Plants that ripen their seed in the fall are exposed to a period of 3 to 6 months at 40F, followed by a shift to 70 for several months.
Cold then warm then cold germinators: As above, but require a shift back to cold to germinate.
Multicycle germinators: May require several alternating periods of warm and cold to germinate. Think about which temperature to start them out at because it often makes a difference. Multicycle germinators may also germinate more quickly when exposed to extended periods of either warm or more usually cold. Pot out seedlings, as they appear without disturbing remaining seed and keep on waiting for more otherwise they will crowd out later germinators.
Hard seed coats: Many seeds have water impermeable seed coats that need to be physically broken by sanding or poking a hole in the side or by acid soak or bacterial digestion before they will germinate. Many of these seeds germinate irregularly over a period of years. The sow it and wait method works well, as long as you prick out the seedling before they grow too big and swallow later germination flushes.
GA3 requirements: Many seeds that would only germinate after prolonged temperature cycling germinate immediately when soaked in a 100 to 1,000 ppm solution of GA3 until they swell; usually 24-48 hrs. is sufficient with germination occurring a week or two later. Placing seed on filter paper soaked with the solution in a baggie until the radicle emerges is another option, especially with large seed. In general, GA3 will often substitute for cold or light requirements. Too much is not a good thing however, as the seedlings will be very stretchy and difficult to grow on. Use the smallest concentration that works. If you actually wish to grow plants and not just watch seed germinate, pay close attention to the concentration.
Two step germinators: Start germination and then stop, until they receive a change in temperature, they may or may not be hypogeal. Be careful not to trash these thinking they have something wrong with them.
Moist storage requirements: Most of the seed that supposedly only germinates when sown fresh actually will germinate years later as long as it is stored moist. Many woodland and bog species have this requirement. Don't go to crazy with this one as many people germinate dry stored trillium and other woodland seeds; they just take longer if they have been dried.
Germination inhibitor removal: Pulp removal by washing, scrubbing, or soaking in water to remove germination inhibitors. Caution, prolonged soaking in water with low available oxygen can drown seed.
If you haven't already done so, buy a copy of Seed Germination Theory and Practice by Norm Deno (get it direct from him: 139 Lenor Dr. State College, PA. 16801)