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Seed Germination & Viability Testing

Whether they are seeds you have saved yourself or seeds you’ve bought and had poor results with, there is a really easy and simple way to test if it is the seeds at fault or something else.

Seed Germination Viability Testing Sweetcorn

Seed Germination Viability Testing Sweetcorn – The result here was near 100%

I’m often contacted by people saying they have sown seeds and nothing has come up. Most often it turns out they’ve been purchased from a supermarket or DIY shed and I suspect they’ve either been over-heated or been frozen in store. Most often over-heated by direct sunlight.

Some of the online suppliers on Ebay run reputable businesses and offer first class products. Others don’t. Once someone has purchased and posted their review it’s too late to do anything when a month or so later the seeds fail to germinate.

When you purchase from a reputable seed merchant by mail order you can be assured the seeds have been stored in optimum conditions and the germination rate will be high. If not they will certainly take your complaint seriously.

The first questions to ask when seeds fail to germinate are:

  • How old are the seeds – how long have they been in store?
  • Have you allowed enough time for them to germinate?

Both the expected seed life in storage and the average days to germination from sowing are shown in the table How Long Seeds Keep For

This does assume that you’ve provided the right conditions for your seeds to get going, correct temperature and enough water etc. If you are unsure about the temperature required check information on the crop you’re growing.  Temperature requirements vary, of course. Tomatoes like it hotter than onions for example.

How to Germination Test Seeds & Assess Viability

To germinate, your seeds need to think they’ve been sown and it’s time to grow.

Take a piece of kitchen roll and dampen it. Onto the damp kitchen roll put a number of seeds, 20 is good if you have a lot, and place into a plastic bag or Tupperware type container.

Put that into somewhere dark and warm; an airing cupboard or a closed cupboard in an occupied room that is warm.

Check the seeds to see which have sprouted. Often they germinate well before the average time, so check frequently. The sweetcorn in the photograph below germinated in just 3 days.

Germinated Sweetcorn

Germinated Sweetcorn After Just 3 Days!

The table How Long Seeds Keep For gives the average germination time for each seed, so you know how long to wait before declaring a failure. If they do fail then at least you haven’t wasted time and effort planting them.

How Long Seeds Keep
Seed Life in Years Avg Days to Germination
Bean, Broad 2 21
Bean, French 2 14
Bean, Runner 2 14
Beet 5 13
Beet Spinach 5 13
Broccoli 5 8
Cabbage 5 8
Carrot 3 16
Cauliflower 5 8
Cucumber 7 9
Kale 4 8
Kohlrabi 4 7
Leek 3 14
Lettuce 4 7
Marrow 6 7
Courgette 6 7
Onion 4 14
Parsley 2 10
Parsnip 1 17
Peas 2 10
Radish 4 6
Salsify 2 12
Spinach 2 11
Swede 2 8
Sweetcorn 3 9
Tomato 3 7
Turnip 2 8

How seeds are stored will make a large difference to their shelf life. The table assumes the seeds have been stored well by which I mean:

  • Dry
  • Consistently Cool
  • Dark

To keep seeds dry, store in an airtight package like a ziploc plastic bag. If in paper envelopes you can keep the envelopes in an airtight tin along with some desiccant like silica gel or even dry rice to absorb any humidity

Keeping dark is easy but cool may be tricky. A fridge at 5ºC would be fine except fridges are usually full of food! Look around for somewhere – don’t forget that cool loft or shed might be as hot as a sauna come the summer.

Germination Rates

Also – germination rates are not simply yes or no. As the seed’s viability drops the percentage germination rate will fall. To compensate for poor germination, just sow more seeds until it is no longer worth while.



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