The Clothiers Site is great for approx. timelines and suggestions for germinating all types of seed. Understand that these are methods that have worked, and not necessarily the only method that will work.

Not all seeds benefit from stratifying. Most digitalis doesn't need it. Your Rudbeckia hirta may respond well to as short as two weeks moist chill to improve germination, but the R. nitida could be better at approx. 40F for many, many weeks and will germinate while still at those cool temps, that one I would place outside to sprout after preparing the pots, let mother nature provide the temperatures.

Calamintha Blue Cloud may germinate well with no moist chill, but sometimes a brief cold period may improve germination and as little as 2 - 4 weeks can be helpful.

Seeds that need stratifying can be placed in tiny ziplocks (look at Staples, office supply or craft stores) with as little as a teaspoon or two of moist sterile sand or moist vermiculite. Date the bags. A small lidded container in your refrigerator will hold seeds/zip locks for a lot of species ;)

When time to sow, you can sow the contents of the bag, vermiculite and all, no need to try to extract smaller seed...with the sterile medium, you shouldn't have mold. You want damp, like a squeezed out sponge, not soggy.

Here is a link that might be useful: Clothiers database

I agree with morz8, the Clothiers germination database is quite reliable. I depend on it often and I've found it to be quite useful.

Regarding your question about stratification medium, you can use a wide variety of different types. I have used paper towels, cotton facial cleaning pads, children's play sand, various potting soils, pine bark, peat moss, etc. So feel free to experiment with any soil-less media.

One thing to keep in mind, as morz8 mentioned, is to keep your media damp, not wet. If you use coffee filters make sure they are damp to the touch and not dripping wet. If you use polyethylene bags in a refrigerator for cold stratification you will find that your media typically stays damp a long time. If your media is soaking wet then the chances are very good that you will end up with moldy seeds.

One thing that I have done in the past to help reduce the chances of mold during stratification is to soak seeds with hard seedcoats in a weak hydrogen peroxide solution for a couple of hours, then move the seeds to a plain water soak for 24-48 hours. I have found this works well with tree and shrub seeds, and I rarely, if ever, have any mold problems. I have *not* tried this method with veggie or flower seeds so I cannot recommend this to you. However, if you have some surplus seeds and wish to experiment, it might be interesting to do so.

Hope this helps.

TYG