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Test for seed viability?

Boxford, MA(Zone 6a)

I just took a VERY cold walk outside through my gardens, and found a few seeds I missed from my collecting last fall (!!!! How did I do THAT???)
Is there a good test for determining the viability of perennial seed (besides sowing them)? This has probably been asked a jillion times before, but I can't find the answer.
The seeds I just snatched are hollyhock, Rose of Sharon, and a few rose hips.

Float a few on water and see whether they sprout.

Calgary, AB(Zone 3a)

I read that if you put seeds in water viable seeds will sink because they're denser and duds will float. Myth? But alot recommend it as a test for seed viability. Thoughts anyone? Note anything that self sows (ie. your hollyhock) won't have it's viability affected by cold or length of time til harvest. I'm still waiting for my amaranthus and perenial snaps to "cook" ie. seed hasn't fully dried YET and a pain to check at my temps. right now (whine, whine)

Dublin, CA(Zone 9a)

That's the usual test I've heard too, but I've had floaters germinate for me, so it's not 100% for sure. Plus once you've dunked the seeds in water, you're probably better off sowing them right away so they don't rot. So I think the best thing to do is sow them and see what happens.

Boxford, MA(Zone 6a)

I dunked my seeds for 24 hrs; all sank except 1. I've folded them up in wet paper towels, put them in a ziploc bag in a dark, warm spot. If they sprout, I have a seed tray all set up.

I've heard the sink/float theory, too; but sometimes a seed packet will say "it's OK if seeds float". Also, I couldn't remove the chaff as clean as I see commercial seed- I'll bet that contributes to floating.

I would like to hear the "science" behind the sink vs. float- any ideas? Moisture content? Lack of oxygen?

Calgary, AB(Zone 3a)

As I understand it viable seed is denser than water so sinks and duds float because air has penetrated the coating or its empty. I too don't think this is a sure fire test for all seed.

It must vary to some degree, because I often sprout seeds in water and many don't sink until a few days have passed and they have absorbed some water. They go on to sprout without any problem. Seeds that have a sort of wing/paper type outer surface will definitely float for a few days regardless of viability.

Calgary, AB(Zone 3a)

My experience too andidandi with the papery surface. Also seeds in fluff. I can never clean all the fluff off and they always float. Some really fine seed doesn't sink for a while either.

Gilmer, TX(Zone 8a)

If you are putting them in water to see if they will sprout, how long do you leave them. I found a bunch of marigolds, (which I don't need) but can't stand to waste a seed

I just throw them into a jar or glass and leave them for a few days. It takes about a week in most cases. Sometimes I change the water. It depends on the seed.

Gilmer, TX(Zone 8a)

Thanks Andidandi, I put the marigolds in water today, then started checking it about 30 minutes later, thinking they'd already have sunk. lol Now, I won't go in and throw them away thinking they are bad

Boxford, MA(Zone 6a)

I just saw an auction on ebay for some "vintage" seed packs from the 60's that still had the seed in them! I was really tempted!! It would be fascinating to see if anything germinated... I guess a lot would depend on how they were stored.

Seeds found in the pyramids have been germinated. It varies by type.

Gilmer, TX(Zone 8a)

Guess they left them so they could grow a garden in the afterlife

Clarence Valley, NSW, Australia

Hi Folks!

There is a difference between 'wet' seed & 'dry' seed. (Tropical seeds, especially fruits, are a separate category entirely, and not covered in the following comments)

Wet seed is mature and harvested when it is still in a moist environment eg Chillies, tomatoes, pumpkins, melons etc. These seeds can be safely graded by the float test, before they have started to dry out (tomatoes & cucumbers are an exception ~ they need to be fermented for 2~3 days first). In float testing, all that sinks will be viable, any that floats may be viable, and the floaters will include any that aren't.

Dry seed is that which is harvested when in a dry state ~ almost all herbs & flowers, beans, peas, Cabbage family, grains, lettuce, celery etc. Testing dry seed by the float method is extremely unreliable and of itself, likely to damage seed.

Deterioration in viability is accelerated by 5 factors ~ moisture, oxygen, heat, light and large fluctuations in temperature. By far the greatest damage is caused by the presence of moisture, especially in the presence of oxygen, as it fosters mould, bacterial growth and seed stress ~ the presence of moisture is like sleep deprivation ~ the seed is 'awake' to the prospect of germination and is not completely dormant.

The accepted procedure for testing seed viability is by germination ~ take say 25 or 50 seed, lay on some paper towelling, cover with more sheets, and moisten. keep in an open plastic bag in a warm (not hot) place with the bag at a slant so that it can drain (not get stagnant). Use a mister to spray the paper towelling to keep moist not wet. Each week for 4 weeks, count & remove the seed which has sprouted. Record results. After 28 days, add the numbers and calculate the total as a fraction of the 25 or 50 you started with. Multiply by 4 or 2, as appropriate, to get a % germination rate.

Personally I don't like to test viability till the season is right for planting, then the removed germinated seed can be planted rather than wasted.

To conserve the greatest seed viability over the longest time possible, seed should be harvested when ripe, (or slightly earlier if rains etc are likely to cause premature sprouting, rotting or mould). Seed should then be dried in a preferably warm and well vetilated situation (eg in seives suspended in mesh freezer baskets etc), large open containers or open paper bags ~ with the latter 2 options check & move seed / pod carrying stems, around to ensure nothing stays wet. Once dry, separate seed from extraneous plant material, pods, chaff etc & dry further, if you can, using redried silica gel in an airtight container. (Don't forget to label & note date of harvest). Once thoroughly dry, package, label & store in a cool, dry, airtight container with fresh silica gel.

All other things being equal, seed viability varies markedly according to species ~ Violet seed has a maximum viability of about 1 week, whereas corn/maize can last from 2 to 10 years, depending on the variety,

Some excellent sources of information can be found at:

Hope that helps folks!

SeedyMaz, Australia

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