“While cleaning seed I observed that some of the seeds floated in the bowl of water they were in, and some sank. I assume that the “floaters” should be discarded because they are likely “empties” anyway.”
While in some isolated cases it might be true that floaters indicate a seed without embryo, it has not been my experience over the years testing many thousands of species, that this old “rule of thumb” has much basis in reality. I would never reject the floaters for this reason alone.
It is perhaps the case that many of these notions are simply accepted without thought, on the basis of common sense and further investigation is deemed unnecessary. However there are other reasons, aside from the lack of an embryo that would cause a seed to float.
And the only way one ever finally does answer the question is to take the experiment through to its logical conclusion- and that is to sprout both floater and sinker. Doing this will lead to surprising results.
Unfortunately, often the myth, rather than the science is what remains.
Norm Deno has the following to say: “The notion that all good seed sinks in water and bad seed floats is just not always true. All Iris setosa seed floats even after a month in water. In fact, it starts to germinate after a couple of weeks floating. Iris pseudoacorus seed floats for a few days and then all sinks. Large sample seed of Cornus amomum were collected from our own colonies and after thorough washing and cleaning, about half the seed floats and half sinks. Both types gave about the same germination both in percent germination and in the rates and other germination characters.”
Answer: Most seeds last for several years, however others have a relatively short life. How do you know if your seeds are still viable? When properly stored in a cool, dry place, seed’s shelf life can be extended. Yet, even then, there is no guarantee that they will still be productive for next season’s planting. There are two easy tests you can take to check to see if there is life left in your old seeds.
Water test: Take your seeds and put them in a container of water. Let them sit for about 15 minutes. Then if the seeds sink, they are still viable; if they float, they most likely will not sprout. This method, in my opinion, is not the best way to check your seeds. For surer results, try performing a germination test.
Germination test: Take some of your seeds, preferably 10, and place them in a row on top of a damp paper towel. Fold over the paper towel and place in a zip-up plastic bag and seal it; this helps to keep the towel moist and protected. Then put in a warm location, like a high shelf or on top of the refrigerator, and check the seeds often—around once a day—to see if they have began to germinate and/or to check the moisture of the paper towel. If it needs more water, carefully mist the towel to where it is damp, but be careful not to apply too much water. Make sure the location you have chosen is away from exposure to direct sunlight. This can overheat your seeds.
Your seeds should begin to germinate in several days up to a couple of weeks, depending on the seed-type. A good rule of thumb is to wait roughly 10 days; however, if you want to give your seeds the best chance, research the germination time of your specific seeds. Once the allotted time has passed, check to see how many have germinated. If you placed 10 seeds on the paper towel, this will be pretty easy to calculate. If less than 5 seeds sprouted, your old packet may not have much success when it comes to planting. If more then 5 sprouted, than your seeds still have a lot of vigor left in them!
Some people wait to perform this germination test around the time of planting, so that the successfully sprouted seeds can be placed directly in their garden—a good way to cut time and ensure the plants will flourish beautifully outdoors.
No matter what step you take to test the viability of your seeds, always remember that every seed is different and your results may vary. With success, you can help your little seedlings sprout into the magnificent, thriving plants they were meant to be.
– See more at: http://www.hortmag.com/weekly-tips/propagation/how-to-know-if-garden-seed-is-viable#sthash.2vMrh4LZ.dpuf