Let's talk about seed stratification. We'll share ways to "fool" seeds into germination by by-passing their natural processes.
There are two main things seeds need to germinate: warmth and moisture. If they have these, then they should germinate.
But there are a few out there that are stubborn and need some "help" so to speak.
No matter what the seed, how big it is, all seeds have a living embryo encased in some sort of protective shell. Generally, the embryo, when conditions are right, does not have any trouble breaking out of the shell.
But there are a few that do.
Some of these are:
Shiso: These need two weeks in the refrigerator. I did an experiment. I put some in the refrigerator for two weeks and some I did not. The ones I put in the refrigerator germinated while the ones that I did not put in the refrigerator did not germinate. I did this because people were saying they were not germinating. It was because they were not following the instructions.
Wildflowers: Many types of wildflowers need a "cold" period in order to germinate. That is why they are to be planted in the fall. But suppose you miss planting in the fall. You can put the seeds in your freezer or refrigerator to "imitate" cold planting and perhaps "fool" the seeds into growing when you plant them in the spring time.
What is seed stratification?
According to Wiki it is: "In horticulture, stratification is a process of treating seeds to simulate natural conditions that the seeds must experience before germination can occur. Many seed species have an embryonic dormancy phase and generally will not sprout until this dormancy is broken."
Basically you are fooling the seeds into believing that the natural conditions for breaking dormancy.
One of these ways is the cold treatment as mentioned above.
Another is taking a file and nicking a seed or scraping it. This allows moisture to get into them easier. I have never tried this. I just plant them and wait for them to come up.
If you know what you are doing you can try sulfuric acid--but I think it best to stay away from this.
Another way is to put them in water and let them soak for a few hours. I tried this with pepper seeds. I soaked for a few hours up to a week. I did read where it said to use hot water (180 degrees). I will I did not see any difference in the germination rate or time.
Experiment and/or read what the seed needs you are trying to grow.