Onion seeds, for example, are only good for a year at most. Maybe you were able to get that two-year-old onion seed to germinate, but chances are, it won’t reach its fullest potential as a plant.
A good number of people probably don’t pay attention to the confusing “days to maturity” label on their seed packets. But if you live in a region with a cooler or shorter growing season, this is one term you need to know.
When should you start seeds? It all comes down to knowing the average last frost date for your specific area. Once you know your last frost date, simply count backward the number of weeks required for each type of plant to be direct sown or transplanted.
Stratification (also known as cold stratification) doesn’t apply to all seeds, but it’s the number-one reason some seeds take their sweet time germinating (or refuse to germinate at all).
If you’re starting seeds inside, most native soil (that is, the regular soil in your garden) is simply too dense for the tiny, closed environment of a seed-starting tray or seedling pot.