Germination Test: How to Test Seeds for Viability

The Germination test measures seed viability and can help gardeners figure out why things are not growing from seed.

Last year my planted carrot seed did not germinate very well. Was the seed still viable, or did I plant the seed too deep? Maybe it got too cold and the seedlings died, or maybe they were eaten by slugs? Did I fertilize enough?

I also collected some tomato and bean seeds last year. I wonder if they are viable? And what about the old seeds I have stored in my fridge; should I use them this year or buy new ones?

These questions can all be answered with a very simple seed viability germination test that you can do at home.

What is a Germination Test?

A germination test or viability test will tell you if your seeds are still alive, and if they will germinate.  More exactly, the test determines the percent of seeds that are alive.

The germination rate is the % of your seeds that will germinate. Anything over 70% indicates that the seed is still good enough to be used.

Why Bother With a Seed Viability Germination Test?

There are many reasons for doing a germination test. Determining the viability rate will let you know how thickly to sow seed in the garden. It will also let you know if it is time to replace the seed with fresh seed.

I am quite sure that my low carrot germination mentioned above was due to old seed. Carrot seed only lasts a few years and if I had done a germination test I would know the answer.

Old Seed

Seed gets old, and dies and once its dead it will not germinate. I’ve added a list of vegetable seeds and their life expectancy at the end of this post.

Recalitrant seed is short lived and even newly purchased seed like trillium could be dead by the time you get it.

Improperly Stored Seed

Seed that is not stored correctly could be dead.

Immature Seed

Seed that you collect or got from a friend may not be mature and will therefore not germinate.

Missing Seed Embryo

Some plants produce seed that is empty inside. Some maples and beech tend to do this. You can collect a handful of seed and find no germination because the seed husks lack a living embryo.

Confirming Germination Process

Dealing with unusual seeds can be difficult because the best germination procedure may not be known. Performing the germination test under different conditions and using different pretreatments can help you narrow down the best way to germinate a particular seed.

Simple Germination Test

I’ll describe the test in simple terms and then in the following sections I’ll discuss a few topics in more detail which will help you increase the accuracy of your test.

Improved Baggy Method

Use the improved baggy method instead of the rolled up paper towel method most people recommend. I have a more detailed video on how I use this method for germinating most of my seed, it is not just for doing a seed viability test.

Take a plastic baggy and insert a piece of paper towel. Add enough water to make the towel moist, but not dripping wet.

Add 10 seeds and close up the bag. Store it upside down at room temperature until the seed germinates.

Count the number of germinated seeds and multiply by 10 to get the germination rate. So if 7 of the 10 seeds germinated, you have a 70% germination rate.

You do not need to use 10 seeds, but if you do, the math is a bit easier.

Using the Germination Rate

What does the germination rate mean? How do you use this information?

If you are sowing seeds in the garden, the germination rate will help you decide on how many seeds to plant. At 100 % you should plant at the spacing you want to end up with. You can expect all seeds to germinate.

If the germination rate is only 70% then you should plant more seeds because 30% of them won’t germinate.

When the germination level drops below 40% consider discarding the seed and getting new ones, unless the seed is very precious and can’t be replaced.

Most people only want a few plants when growing perennials or trees from seed so a low germination rate is not really a problem. Start more seeds knowing that most will not germinate.

Selecting Your Seeds

The germination test can be done with any 10 seeds, but if you really want your results to mean something you should be careful how you select those 10 seeds.

In any batch of seeds there is always some size variability and small seeds may not germinate as well as larger ones. Some might be more or less dried, others might have different colors. For the test to be accurate you want to make sure your set of 10 seeds represents the whole batch – you want to randomize the selection process.

One way to do this is to dump out all the seeds of a particular type. Take a knife or similar flat blade and divide the pile into two. Take one of the piles and divide it into two again. Keep repeating this until you have a pile with about 10 seeds in it. This process will help randomize the selection to include some of every type; large, small, brown, black etc.

Waiting for Germination

Once the seeds are tucked away in the baggy, it is time to wait for the seeds to germinate, but how long should you wait? This really depends on the seed since each seed germinates at a different pace. There is variability both between seeds of the same type and between different types of seed.

I have had some perennials germinate within 24 hours at room temperature, and some, like clematis, take a year. Most vegetable seed will germinate in 5 – 10 days, but hot peppers can take 30 days.

Step one is to research the seed and find out how it should be germinated. Most vegetables germinate just fine at room temperature. Other types of plants may need to receive one or more pretreatment methods such as:

• scarification (nicking the seed coat)
• soaking and washing
• stratification (temperature cycling)
• GA3 hormone treatment

The germination test should use the same method you will be using to grow plants from seed.

It is also important to wait long enough so that all of the viable seed germinates. In most cases this takes place over several days. Wait until the first seed germinates and then monitor them every day until you reach a point where no more seeds germinate. Then count the germinated seeds.

This does not work as well for seeds that germinate very slowly over many weeks or even months. In this case it is a good idea to check the baggy every few days, remove the germinated seed, and track the number of seeds you remove. Then wait an extra month or two until the very last ones have germinated.

How Long Do Seeds Live?

This varies a lot and depends on many variables including the method of storage. The following is a list of the expected life span (in years) for some common vegetables. The number in brackets is the number of days for seed to germinate at room temperature.

• Bean 4 (6-14)
• Beet 4 (5-15)
• Cabbage 6 (5-10)
• Carrot 3 (14-21)
• Corn 2 (7-14)
• Cucumber 10 (3-10)
• Lettuce 5 (7-14)
• Onion 2 (10-20)
• Pea 3 (9-13)
• Pepper 4 (7-30)
• Radish 4 (3-7)
• Tomato 6 (5-10)

My experience is that the seed lasts longer than indicated on this list. I have had tomato seeds germinate after being in the fridge for 10 years.