If you find such a holy grail, be sure to let the rest of us know!
Obviously, there are better and worse lists/compilations, trustworthy and not so much so, more and less complete. There is no list that even nears the completion that you wish.
Your frustrations are understandable, but not well deserved. Sometimes the answer just isn't known. Before the internet, the only way to pass along such information was via land line telephone, post mail or on the ground manual research in libraries. Such published detailed information was scarce and incomprehensive. The sources usually being university based scientific papers, accessible only in a particular library(s) somewhere in the world. I find it incredible that there is even any moneys that are dedicated to this kind of research, and I am grateful. It's taken a long time to get to where we are now. The web is a wonderful thing, and it is an extension of all these prior processes. The web is an incarnation a thousand times more efficient that anything previous, and is still only as good as those who contribute. I too, get frustrated when information is incomplete. My point is, that at least something is there at all.
As you learn about about seed germination, you will discover that your initial frustrations are not as important as you had thought: mother nature is always a continuum and there are rarely cutthroat rules. I always say that in nature, the only unbroken rule is that there are no unbroken rules. The more you learn, the more you find out that there are even more things you don't know.
I am always on the lookout for such information as close to scientifically rendered as possible: when environmental parameters are clearly delineated, as well as the results. This rarely happens to any large scale, and often our only sources are relatively useless anecdotal information.
Statements like "Seed germinated at room temperature for me". Depending on the source, it is more or less believable and more or less could be read into it or assumed. Is it reasonable to assume that the seeds were viable to begin with? We don't know how the seed was stored prior, how many seeds were involved, the percentage of seeds that actually germinated, was sterile-pasteurized-unpasteurized soil used, was it inside or outside, etc. We don't even know (we just assume) that "germination" also included sprouting above the media surface. But for empirical data collecting, what can you actually gain unequivocally from this?
-- that seed
might germinate and emerge at room temp. That's all.
To your original questions, if you don't know about Dr. Deno's books, then you haven't read "The Ultimate Resource for Seed Collectors". It uses scientifically based data for actual germination of more than 4800 species. A consolidated info spreadsheet is found here:
https://garden.org/thread/view...
1.What does 55F mean - some statistical function of high and/or low temperatures over some time span, average soil temperature at some unspecified depth (does any weather site actually provide this info?), something else?
-- If the data is for indoors, it is fairly safe to assume it is the ambient seed temperature, i.e. whatever the media is that the seed is in. Even then, there are variables. If it is under lights and covered with clear plastic, you can add another 5-15°F to the room's temp, and realize that when the lights are off the temp will be whatever is ambient.
__ If it is outside, what is meant can be a crap shoot. Unless specified, I suppose I would assume air temp, which depending on the time of season, one might be able to extrapolate the temperature of the soil. The soil temp is rarely the temp of the air.
2. Does "55F is preferred" mean the plant will do a lot better when you plant the seed at this temp, or if you plant it earlier will it just wait until it's more around 55F?
-- We can assume that the seed will sprout better at around 55°F. A lot better? unknown. I would expect it to germinate slower at 50 and faster at 60. Whether the particular type of seed will germinate much above or much below these temps is unknown. This answered, tempered with the above (#1) explanation.
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There are always exceptions, but a generalization for seeds is that most fall into a two groups for ACTUAL SEED GERMINATION temperature:
Around 40°F - range from above freezing to about 50°F
Around 70°F - range above 60°F
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3. Why the hell would it suggest planting the seed 2-4 weeks before last frost, when temps are in the range of say 24F-40F, right before stating this is really non-optimal.
Many kinds of seed need a preconditioning that is different from the conditions needed for when actual germination occurs
4. What are the cases when you need to do stratification? I'm guessing you wouldn't need to if planted 2-4 weeks before average last frost but would if freezing temps are no longer happening, but it doesn't state this.
The cases are many and variable, depending particular seed types. You will only know through research. Some might need a cold stratification for 2 weeks, some might be 4 months. Some might need multiple cycles and cold and warm at certain durations. About the only real generalization is that there are a greater percentage of wood plant seed that need cold stratification than non-woody.
5. What is the recommended stratification method?
Assuming you mean cold stratification, anything that gives 33-45°F with moisture and air. People usually do this in a pot, jar or baggie with moist peat, sphagnum, vermiculite or a light soil media. You cannot submerge or float the seeds in water for stratification.
