We all know if we buy seeds in bulk they end up being much cheaper. However, the problem is if you buy more seeds than you need for the season they might not be viable next year. Can someone tell how long various annual plant seeds are viable for eg zinnia, petunia, phlox, nasturtium, sunflower, poppy, wildflowers etc
Good seed companies mention the expiry date on packets & the seeds are viable during the mentioned period provided if stored properly. We can’t say any things about the seeds where expiry is not mentioned because we don’t know how much old they are when come to us. There is no fixed rule to all type of seeds because some germinate best when sowed fresh but most type of plant seeds don’t germinate when sowed fresh because these seeds need some shelf life to overcome the inhibitor present in the seed which destroy over time, some species needs few weeks, some needs three or six months & some need even 3 years. Still there is lot of research work required on seed germination to discover all perimeters of seed species. Till date the best source of information on the germination of seeds is 'Seed Germination, Theory and Practice' by Norm Deno. This book is basically a research manual describing 4000 species.
You can download the book in PDF format from the USDA National Agriculture Library.