Before you begin, how large is your garden? Propagating your own seeds can take up a lot of space.
As an example: My Triffid! This is a mini cabbage. Just ONE mini cabbage. It is currently about a metre square. It’s taken over a large part of my garden, swamped the peas and taken over the beets…
If you’ve got enough room, then propagation, or seed banking is worthwhile.
If you don’t have the room, then seed swapping is also a great way to get new plants. When you buy a pack of seeds there is generally way more than you can use, consider swapping them out with other gardeners (either seeds or seedlings). It’s a great way to minimise on cost and maximise on variety.
Somes seeds last longer than others.
Onion and parsnip have a life expectancy of a year.
Sweetcorn, leek, and pepper two years
carrot, celery, pea, bean and spinach three years
tomato, turnip, pumpkin, cabbage, cauliflower, eggplant four years
radish and cucumber five years
Hybrid seeds -F1 First filial generation are plants that are generally more uniform and vigorous however seed saving will not yield seeds that resemble the parent plant. (if they produce seed at all)