The Peat-Free Diet: Seed viability and germination testing

Seed viability

If you sow a batch of seeds and none of them germinate then it’s easy to imagine that you’ve done something wrong. Perhaps the temperature was too low (or too high), or you didn’t get the watering right. Perhaps the seeds succumbed to a pest or a disease before they even emerged from the soil. All of these are possibilities, but it’s also possible that the seed you sowed was not viable – that it was not capable of germination.

If we think back to the analogy of a seed being a survival pod, with a plant embryo lying dormant inside, then it’s easy to realise that they don’t have an unlimited lifespan. Eventually they will run out of the energy needed to maintain the life-support system, and when that happens the embryo will die. How long this process takes is very much dependent on the plant species, and it’s not a black and white thing; the percentage of viable seed in any given batch drops over time.

Seed packets often come with a Use By or Sow By date for this reason, but you can also find tables of expected seed lifespans on the internet.

It’s also possible that the seed was not viable to begin with. We can’t see what’s inside the seed, but variations in plant health and environmental conditions mean that not every seed that is created and released is alive.

Seed Banks (like the Millennium Seed Bank at Kew, Sussex or the Doomsday vault in Svalbard, Norway) go to great lengths to ensure that the seeds they collect for the future are viable and remain so. Most seeds are what scientists call orthodox, which means that they can be stored for long periods of time at low temperatures if they have been thoroughly (but not completely) dried. Stored seed batches are tested for viability at regular intervals.