It’s a familiar scenario: just before heading out to plant the garden, you take out your jar or shoe box of miscellaneous seed packages saved for years, with perhaps a few marigold or squash seeds you’ve harvested from the garden, and try to decide which are worth gambling on this year. While survivalists may save seeds to ward off coming Endtime starvation, most of us don’t save seeds to survive, but because packages of seeds often contain way more seeds than we need. Being thrifty New Englanders we put the leftovers away for another season. When stored properly, these extra flower and vegetable seeds have a good shelf life, although the germination rate naturally drops over time.

So there you are, ready to go, beds fertilized and raked smooth, weather warming, perhaps even a fine May rain predicted to help water-in newly set out plants and seeds. You open up your magic seed box and pull out six different crumpled packs of sweet corn seed, with dates ranging back to 2015. Deciding which to plant and which to discard can cause a gardener to break out in hives. A quick look at an online seed viability chart reveals that spinach, lettuce, parsnip, and corn seeds are generally only viable for about a year, bean and corn seeds may germinate after two years, and the seeds of many squash varieties are often good for three or four years. You could have done some germination tests, back a few weeks ago — moistening a paper towel or coffee filter, folding 10 seeds inside and putting them in a ziplock bag in a warmish place for a week to see what percentage of them sprout. If 8 seeds sprout, you will know you have about 80 percent viability for that particular plant variety.

But it’s too late for that; you’re eager to plant. One simple, last-minute viability test you can perform that, while not a perfect indicator, is still fairly accurate is to drop a few of your questionable seeds in a jar of water. If they sink, they’re good. If they float, they’re not. Once you have determined that your seeds are still useable, go ahead and plant them, but be extra generous in the sowing. If the germination rate is better than expected, you can always thin out those that are too close together. If there are big gaps in the seedlings, you can always purchase some new seeds and fill in the gaps.

In doing this, you’re acting a bit like Mother Nature, who isn’t perfectly scientific either. In the natural world, incomplete pollination can result in a high proportion of empty seeds. They look like seeds, but there is no embryo, or one which is only partly developed. Some plants require 15 to 20 visits to each flower by a pollinator in order to produce a good seed pod or fruit. Different seeds from the same seed pod will have different degrees of viability even in the embryo, and all these seeds, good or bad, have to be collected after they have fully ripened.

Further complicating things is hybridization. As flowers and vegetables are increasingly hybridized to produce a color or form that is remote from the natural parents, the viability of the seed germ is reduced. You may choose a newly offered variety of a favorite flower and find that the seeds are hard to start, or the seedlings take forever to reach flowering stage. But what can you expect from a flower that’s been yellow for the last five thousand years, but now must be red? We can’t forget about the power of natural selection to make good, viable plants and seeds.

We’d also like to believe that seedsmen collect and clean their seed and immediately place the seed in an environment in which its viability does not deteriorate. However, big seed companies cannot grow all the seed they sell, so much of their seed comes from outside suppliers. So you are purchasing seed whose present condition is unknown unless the packet is marked with its germination rate. With some suppliers, none of the packets are marked as having been tested. Suppliers who guarantee their seeds offer the best buy in the long run.

Thinking ahead, if you’re creating your own seed bank by saving or harvesting your own seeds, store seeds in their original packages if possible, or in a labeled envelope (include the date) in a jar or cookie tin with a tight-fitting lid, protected from light and moisture. Cool temperatures are recommended. If you have a frost-free refrigerator, it has the perfect cool, dry and constant temperature for seed-saving. Some experts further advise placing rice or powdered milk in the container, to absorb moisture.

Instead of saving seeds for another year, some gardeners intentionally over-plant, to account for thinning and the inevitable loss of a few seedlings. Even better, if you have extra seeds, stagger plantings of beans, lettuce, and other crops throughout the season, so you’ll always have a fresh harvest coming along. But the best thing to do with extra seeds is to share them with a friend. That way, you’ll have someone to compare notes with, and you’ll have no dubious leftovers, giving you an excuse to try something new every season.