More about SEEDS!
About our seed germination tests
I conduct viability tests by observing (counting) the seeds’ % germination when placed under proper germination conditions. I do this on a yearly basis, right before I prepare to sell them, in early winter. The dates (month-year) and the %germination are indicated. Each packet is corrected for the right number of viable seeds according to their score. I also observe their general vigor in germination as a supplemental information on my seeds’ quality. Now, more about seed storage and seed longevity!
1. A little about Seed Longevity
Most agricultural and garden seeds fall into the category common to most well-known seeds, called orthodox seed(1). They have in common a good longevity in storage. The other group is called Recalcitrant seed, and comprises many tree seeds, nuts, some tropical plants. These cannot stand very long in storage if dried too much. (Very summarized, but you get the picture). The first type of seed is also able to spend some time under a nearly-still-life under storage, the length of which is species-dependant and varies from 1 year to nearly 10. You can find a list of many types of garden seeds and their mean longevity at room temperature in How to save your own seeds, a publication available from Seeds of Diversity - and other seed charts on the Web. Many charts vary and you may notice that some sources shorten the seed lifespan in storage more than others, perhaps because they consider most people don’t store seeds under optimal conditions.
Seed germination and Seed Longevity are two very related topics, like two opposites: so here we go,
Upon sowing, seeds imbibe a little water, germination processes start (enzymatic activity brings nutrients to the embryo -the mini plant inside the seed- it starts to develop, elongates its root into the soil and some stem/leaf parts that reach into the air).
To germinate and grow a seed, we will allow
-warmth (between 40°F to 86°F, different needs by genera/species)
As a reminder, any condition that helps a seed to germinate will make it ‘age’ faster and decrease its quality in storage.
To keep a seed as long as possible, we will store it
- with less oxygen (sealed)
The seed is dried (air-dried if in a dry area), stored sealed (and well labeled if you plan long-term storage!) placed right into the refrigerator (for a 10-year or more leap) or into the freezer (for years and years of storage!). As mentioned in the Seed of Diversity booklet, when time comes to bring back seeds to room temperature for sowing, wait until the contents have reached room temperature before opening the bag or jar -or moisture may condense on the seeds (like droplets of water on an ice-cold drink on a wet summer day) and may cause damage to those put back into storage.
How much longer can we keep a seed viable, well dried and sealed in cold storage?
(You guessed why Svalbard Global Seed Vault was built into permafrost). According to some experiments and estimates from germination percentage graphs taken at intervals from stored seed, once well dried (less humidity than air-dried seed) and stored at -20°C (-4°F) (which is a little lower than most household freezers) a seed could last up to:
400-800 years (!) for the Onion
50-100 years for Sunflower
about 300 years for Brassicas seeds (mustard and rutabaga)
almost 300 for Pumpkin
1300 years for Millet (Setaria)
200-300 years for Soybean
3000-4000 for Peas and Beans (!!!) (2)
Another study suggests that very dry seed, if stored sealed (airtight) can still handle long periods (100+ years) of storage at room temperature without losing viability. (3)
2. Some seeds are DORMANT
- Fresh Seeds are often dormant, even tomatoes to some extent: that’s why freshly harvested seeds of some tomato (and other) varieties have better germination scores the second year after harvest! I have noted up to about 10%. I have even seen one of my varieties under development (not stable nor available) that yielded only 50% germination in the first week then all the rest sprouted weeks later!
To sprout, some seeds require leaching (mimics lots of rain), or be exposed to light (germinate! there is plenty of space for you.), or follow a cold period (ok spring is back, you can sprout), or be nicked or scratched (scarification - like passing through the gut of a bird).
-Strawberry seeds are not always highly dormant but a 1-2 months dormancy-breaking cold period (called stratification) will generally help give good germination scores. (They also respond well to light after refrigeration -surface sow on the moistened soil mix.)
To look further
Seed Production and storage Basics for the home garden:
How to save your own seeds. A handbook for small-scale seed production. by Seeds of Diversity Canada
More in-depth references and reading suggestions
(1) Hartmann, H.T., Kester, D.E., Davies F.T.Jr, Geneve, R. (2002) Hartmann and Kester's plant propagation: Principles and practices, 7th ed, Prentice Hall. Upper Saddle River NJ
(2) International Board for Plant Genetic Resources. Seed Storage Behaviour: A compendium. Handbook for Genebanks no.4. (Available Online)
(3) Steiner, A. Ruckenbauer, P. (1995). Germination of 110 year-old cereal and weed seeds, the Vienna sample of 1877. Verification of effective ultra-dry storage at ambient temperature. Seed Science and Research, 5(4) 195-199.