What is Seed Viability and How to Test It?


Seeds are the womb of a plant. They are fertile, mature ovules where an embryonic plant lies dormant. Nutrients are also stored inside the seed that the embryo consumes, and once it has taken in all these nutrients, the embryo must then either be planted to grow or else it will begin to age and lose its viability.

Seed viability refers to a seed’s ability to germinate. There are ways to test your seeds’ viability at home using a paper towel or moist sand to encourage germination. Some seeds can also be tested by seeing if they float.

If you’re unsure how viable your seeds are, this article will explain what seed viability is as well as how you can test for it with simple, reliable methods. Also, germination rates will be discussed and what they mean in terms of seed viability.            

What Does Seed Viability Mean?

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Seed viability refers to the measurement of how capable a seed is of germinating under the right conditions. In other words, it determines if a seed is alive or not. Some confuse viability with germination, as they look the same. But viability measures the life inside the seed, whereas germination expressly defines whether that life sprouts out of the seed or not.

Factors That Affect Seed Viability

A seed’s coat, poor pollination, or even a mechanical injury that occurs while harvesting a seed may compromise its viability. After that, how and under what conditions you store your seeds will affect how long your seeds stay viable. And there are several considerations to consider when storing seeds, including the levels and presence of:

  • Moisture
  • Temperature
  • Humidity
  • Light
  • Insects
  • Storage container

Moisture is the most crucial component, as too much moisture will cause mold to develop and kill the seed. Temperature is just as critical: seeds stored in warm, bright, humid environments will lose viability much quicker than seeds stored in cool, dark, dry environments.

On average, a humidity level of 5 – 10 percent and temperatures between 32 and 41 degrees Fahrenheit (0 and 5 degrees Celsius) are ideal for maintaining your seeds’ viability. For most seeds, storage in an air-tight container (preferably glass) inside the refrigerator where it is dark and cold is the best option. If this is not an option, store in a basement, garage, or closet with a shared exterior wall—ideally, you’re looking for someplace that is likely to stay cooler than, say, your kitchen cabinets or a pantry.

Are New Seeds More Viable Than Old Ones?

Throughout a seed’s physiological maturity, viability is highest and will gradually decline afterward until it eventually dies. And while most seeds will develop normally, some may accrue abnormalities that may affect how long they may be viable, if at all.

But this is perhaps where some may have confused viability with germination—or more specifically, germination rate, which we will discuss below. A seed will either be viable or not, that is, it is either alive or dead, period. So, to ask if new seeds are more viable than old is a bit misleading. If the seed is viable and the conditions are good, then the seed will germinate.

However, the seed will lose some of its vigor as it ages, and you may have an issue with how well the plant itself develops. For example, a melon seed can stay viable for up to six years. And while it may still germinate well at year four, it is likely to produce weak growth and very little fruit. It is also possible that the plant may be more susceptible to disease than it would be had the seed been planted earlier.

Therefore, you should plant a seed when it is as young as possible, or early during its viability period. This will ultimately produce a healthier plant.

How Long Do Seeds Last?

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Like all living things, seeds will eventually die out, or in our new vernacular, they lose their viability. Along with this, there are ways viability can be either shortened or lengthened, as we’ve discussed.

Unfortunately, there is not a general one-size-fits-all kind of answer. Seed longevity will vary from plant to plant, and even multiple seeds harvested from the same source will each have their own unique lifespan.

Packaged seeds will come with a “packaged on” or “plant by” date printed on the label that you can use as a general guide for their viability. But ultimately, the conditions in which you store your seeds will have the biggest effect on how long they remain viable.

Here’s a list of a few common plants and their seed viability in years. Keep in mind that these are averages based on ideal conditions, and there may be differences between plant variations as well.

Fruits & VegetablesHerbsFlowers
Asparagus3Arugula3 – 4Amaranthus4 – 5
Broccoli3 – 5Basil3 – 5Anthemis2
Carrots3 – 4Chives1 – 3Calendula5 – 6
Cucumber3 – 6Cilantro1 – 5Cosmos3 – 4
Corn1 – 3Dill1 – 5Hollyhock2 – 3
Lettuce5 – 6Oregano1 – 4Linum1 – 2
Onion1Parsley1 – 4Marigold2 – 3
Peppers2 – 5Rosemary1 – 4Nigella2
Spinach3 – 5Thyme1 – 4Pansy2
Tomato3 – 7Sage1 – 3Petunia2 – 3

If you are unsure if your seeds are still viable or not, you can easily test some seeds to see if they germinate. It is best to test any stored seeds for germination rates before planting them and this is especially recommended if you doubt their age.

Ways to Calculate the Germination Rate of Seeds

As mentioned above, some tend to think viability and germination rates are the same thing. This is understandable because the germination rate of a batch of seeds is determined by how many viable seeds are in that batch. You might have someone say to you, “these seeds are very viable,” when they most likely mean that they have a high germination rate.

Germination rates are calculated by testing a small batch of seeds to see how many of them are viable. It is expressed as a percentage determined by the following formula:

Germination Rate = Number of seeds that germinate / Total number of seeds tested

So, if you test ten seeds, for example, and seven germinate, seven divided by ten is 0.7, which means this batch of ten seeds has a germination rate of 70 percent.

You should test a batch of a significant size to yield the most accurate results. Additionally, the seeds should be a fair representation of all shapes, sizes, and colors a particular seed harvest may contain. A batch of ten seeds is a good minimum amount to test if your supply is limited, but if the seeds you have are rarer and more expensive, you may wish to only test a few (or just plant them and hope for the best, if that is the case).

What Is the Targeted Germination Rate?

For many types of plants, anywhere from 80 to 100 percent germination rate is considered excellent. Reputable seed distributors aim for 90 percent or higher when possible. Even 70 percent could be considered good, if not great, for some varieties.

This translates into how many seeds you must sow within a space to increase your chances of obtaining the number of plants you desire.

What is a Bad Germination Rate? Should You Throw Out Seeds with Bad Germination Rates?

In many ways, it is pretty much up to you to decide when you should throw your seeds out. Lower germination rates of 30 to 60 percent are not ideal, but this just means you would have to plant two or three seeds in one space to increase your odds of having one of them actually sprout and take root.

However, low germination rates also imply the seeds might be old, and any seeds that are still viable may not be capable of producing strong plants. Therefore, depending on the type of seed and how expensive it is, it may not be worth the time or resources needed even to try and plant seeds that have a 50 percent germination rate or lower.

In the end, it will be up to you whether you sow or throw your seeds away.

Types of Germination Tests

Paper Towel Germination Test

This method of testing is tried and true. It is the most common and most accurate way to test viability. It may take only a few days for germination, while some seeds may take up to two weeks or more.

To test seeds:

  1. Dampen a paper towel and fold it in half.
  2. Put ten seeds on the paper towel, making sure they don’t touch one another, and fold the paper towel in half again to cover the seeds.
  3. Put this into a sealed baggie or covered mason jar—anything that will contain the moisture—and place it in a suitable location for the seeds’ germination.

Sand Germination Test

This test is done essentially the same way as the paper towel method, except the sand is used to surround the seed, and you must maintain the moisture in the sand. Seeds with mechanical damage or pathogen problems may benefit from this method. You may wish to use this method if you plan on planting your germinated seeds, as this method will suppress fungi from developing during the testing process.

Germination will typically occur within 7-10 days, although this may vary from seed to seed.

To test seeds using the sand method:

  1. Fill a short-wall container with clean sand
  2. Place seeds on the sand
  3. Cover the seeds with another layer of sand
  4. Use a spritzer bottle of water to keep sand moist

Float Germination Test

This is the quickest method to test viability, although it will not work for all seeds. It is best for medium to large seeds like peas, peppers, corn, and tomatoes, but it will not work for tiny seeds like lettuce or carrots.

To test seeds using the float method:

  1. Put seeds into a glass or bowl filled with warm water
  2. Allow them to sit for 15 to 30 minutes
  3. Sterile seeds will float. This is because they do not contain an embryo and therefore are lighter in weight. Heavier seeds will sink, indicating that they are likely to be viable.

Closing Thoughts

Seed viability is critical knowledge for any grower to know. This can easily be determined by the paper towel, sand, or float methods. By testing for viability and determining germination rates, you can ensure a more productive yield in the upcoming growing season.

Here are Some of my Favorite Gardening Products and Tools

Thank you for reading this article. I hope you found it helpful for growing some new plants in your home or garden. Here are some products I like that I hope you’ll also find helpful. These are affiliate links, and I am compensated for referring traffic. But in all honesty, these are the exact product that I use or recommend to everyone.

Soil: For high-quality soil, I really like Fox Farm Ocean Forest. I do all my growing in containers and this soil has worked great for me. I like how they use nutrient-rich contents like earthworm castings, bat guano, and composted crab and fish.

Fertilizer: Currently I am using a seaweed-based organic fertilizer call Neptunes Harvest. This is a great milder fertilizer option if you want to use something organic. If you want a more powerful fertilizer, I recommend Fox Farm Liquid Nutrient Trio, lots of people have had great growing success with this product.

Pruning Shears: Pruning shears are one of the most useful gardening tools to have because it’s important to prune your plants to keep them healthy. The pruning shears I recommend are the Gonicc 8’’ pruning shears. I like them because they are built sturdy and work both on bigger and smaller plants, so you don’t need to have multiple pruning shears.

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