Testing your seed for viability

Aug 20, 2023 | Gardening tips

It can be disappointing to sow seed and none of it comes up. There’s an easy way to check whether your seed is viable and how viable it is. Now is the time to test any seed you might want to sow this spring.

Seeds have varied lifespans. Parsnip and angelica for example need to be sown fresh soon after they are harvested and certainly within a few months. The onion family including chives, leeks and garlic are the same. Sometimes these are referred to as ‘very sensitive seed’. Short life expectancy seed (2-3 years) includes carrot, celery and corn. Midlife expectancy (4-5 years) applies to beans, lettuce, peas, peppers, radishes and Swiss chard. Long life expectancy (5 years plus) applies to tomato, and to many seeds that are best bought commercially because they cross-pollinate in home gardens, often producing inferior off-spring. These include brassicas, pumpkins, melons and cucumbers.

To test for viability, you will need:

  • Kitchen paper
  • Permanent pen
  • Zip-lock bag
  • Seed

In short, you will label the kitchen paper, wet it, spread the seed, roll it up and place it in a closed zip-lock bag for 7 days in a warm place. After 7 days you will unwrap it and check whether the seed has germinated. If it has, it won’t be suitable for planting but it will indicate whether your seed is viable.

Here’s the detail:

  • Tear off as many sheets of kitchen towel as you have seed packets to test
  • Write the name of each seed type on the BOTTOM of the sheet in permanent pen
  • Stack the sheets neatly on top of each other and dip them in water. Either press them down to expel as much water as possible or fold the bundle in half and do the same so that you end up with damp but not wet sheets. Don’t twist or scrunch the sheets as this makes them very difficult to separate
  • Gently peel one labelled sheet off at a time and place on a bench – be careful as they will tear easily
  • Sprinkle seed across the TOP of the sheet
  • Roll the sheet up tightly from the TOP to the bottom. This ensures that when you unroll, the label will be visible
  • Fold the roll in half and place it in a zip-lock bag unless you have a very wide bag which will accommodate the width of the kitchen paper. Zip the bag closed. (You can put multiple rolls in one bag)
  • Leave the bag in a warm place for 7 days
  • Unroll each bundle and check whether the seeds have germinated

To test for percentage of seeds that are viable:

  • Place exactly 10 seeds across the top of the sheet
  • Count the number of seeds that have germinated and multiply by 10. This gives you your percentage e.g. If 7 seeds out of 10 germinate, you have 70% viability

NB (It is easier working with medium to large seeds. It can be difficult to count out 10 very tiny seeds but you will get a rough idea even if you sprinkle a few extra).

Don’t be discouraged if you get a low germination rate. Simply sow more seed to make up for this. If for example you want 50 seedlings and your germination rate is 25%, (i.e 25 out of every 100 seeds will germinate) then sow 200 seeds to arrive at 50 seedlings.

Written by Robin Gale-Baker