Testing old seeds for germination is an essential skill for a gardener, especially if you come across some old seeds. How long seeds last vary plant to plant, though a good rule of thumb is 3-7 years. So, if you have some questionably aged seeds, how do you test if they’ll grow?
You can test old seeds for germination by floating them in water or germinating a few in a moist environment. Typically, the seeds will sprout in about ten days if they are still viable. However, some seeds take longer, so check the germination length before throwing them out.
In the rest of this article, I will discuss a few ways to test your old seeds for germination and what to watch out for with older seeds. Plus, some frequently asked questions about old seed sprouting. So if you want to learn more about testing old seeds, read on.
1. Check the Old Seeds for Visible Problems
First, before you begin any testing method, it’s essential to check that the seeds are worth testing. For an old seed to remain viable, it is best to store them properly. So what is the correct way to keep seeds for later use?
Signs your seeds aren’t viable anymore:
- You stored your seeds somewhere damp, and your seeds got wet.
- You kept them somewhere hot or in the sun.
- You failed to keep them in a sealed container.
Seeds stored in a cool, dry place are more likely to have success sprouting when old. However, testing their viability before throwing them out doesn’t hurt so long as they don’t appear damaged or moldy.
2. Perform a Float Test To See if Your Old Seeds Are Viable
The most straightforward test to perform for germination is the float test. This test isn’t the most accurate, but it’s a good indicator of your seed viability. To conduct this test, you will need about 5-10 seeds. The more seeds you use, the better indication you’ll get of the seeds’ ability to germinate.
You will need the following:
- Several seeds
- Water
- A jar or other lidded container
How to perform the float test:
- Fill your glass or container with water. A clear jar or container is ideal, so you can see all your seeds and how many of them sink vs. float.
- Sprinkle your seeds into the water and give the jar a good shake. The germinating seeds will sink to the bottom of the glass while the dead ones will float.
- Leave the jar for a few hours to settle. After several hours the seeds will settle, and you’ll get a better idea of which seeds will grow.
- Discard the seeds that float and save the ones that sunk. Floating seeds can be composted or thrown out. You can plant the seeds that sink. However, if you don’t plan on growing them immediately, ensure they have time to dry out before being stored again.
It’s important to note that sometimes this method can be wrong, and some floating seeds might germinate and vice versa. However, for the most part, float testing is an accurate method. Additionally, there are several ways to perform the float test. For example, some people add soap to the water to reduce water tension, and others soak their seeds before testing.
Suppose you are more of a visual learner; I recommend watching the Balconia Gardens video on testing dead seeds via the water method. She does a fantastic job of reviewing each step and the reasoning behind the float method.
Why the Float Test Works
Performing the float test is excellent, but understanding why this method works is also essential. As I previously stated, viable seeds will sink to the bottom of the glass. This sinking action is due to the more dense viable seeds, while the floating seeds are empty or dried out.
However, good seeds will occasionally stay floating, and you might throw out viable seeds accidentally. So, some people consider this method less accurate because of this problem. However, at least you are assured that the seeds on the bottom of the glass will all be viable.
3. Germinate the Old Seeds With a Paper Towel and Bag
Another excellent method to test your old seeds’ ability to germinate is by utilizing a damp paper towel and a ziplock bag. This method is relatively straightforward; chances are you did this in school as a child. The best way to ensure your seed will grow is to test a few by trying to germinate them.
There are several reasons why using this tried and tested method works; which I explore in my article: 9 Reasons Why You Would Germinate Seeds in a Paper Towel
What you will need:
- Several seeds
- A paper towel
- A ziplock bag
- Tape
How to germinate old seeds using a zip lock bag and paper towel:
- Moisten your paper towel and lay it out. The paper towel needs to be damp to help the seeds sprout. This moisture will be the seeds’ only water source as they grow.
- Organize the seeds along the top half of the paper towel. You only want the seeds on half the paper towel because you’re going to fold it in half to encompass the seeds completely.
- Fold the paper towel to cover your seeds. Ensure a damp paper towel completely covers the seeds on both sides.
- Place the paper towel seeds into a ziplock bag. Do your best to ensure the towel doesn’t get all folded up. You want to keep it as smooth as possible so the seeds can get sunlight. Ensure the bag gets a good seal since you want to trap the moisture.
- Tape the bag to a warm window or under a grow light. Don’t tape the seeds directly onto the glass if the weather is too hot or cold. Instead, put them back a little. Seeds that get too warm or cold won’t germinate.
- Wait about ten days. If the seeds don’t sprout in 10 days, they are likely dead. However, some plant seeds take longer to germinate, so double-check before tossing your ziplock seeds.
This method is probably the most accurate way to test that your seeds are viable and will thrive. However, to ensure the test’s accuracy, it’s crucial to try germinating several seeds.
4. Sprout the Old Seeds Using a Glass Jar
Next, you can try sprouting your seeds using the glass jar method. This method is similar to the zip lock bag method, simply with a glass jar. However, it’s also super practical and great if you want to limit your plastic use.
What you will need:
- Several seeds
- A paper towel
- A jar
How to test seeds germination ability using a glass jar:
- Moisten your paper towel.
- Arrange the seeds on half the paper towel.
- Fold the paper towel in half to cover the seeds completely.
- Place the paper towel and seeds into the jar and seal.
- Put the jar somewhere warm, like a window seal.
- Wait.
As you can see, the method is similar. The only difference is that you must arrange the seeds to fit into the jar and evenly get sunlight. This method works just as well as the ziplock bag method and is better for the planet. If the seeds are reasonable, you will likely have results in 10 days.
5. Test the Old Seeds in Sand To See if They Grow
Finally, there is the sand test. This test is simple and incredibly effective if you wish to move the seeds immediately to your garden once they have sprouted. Sand is an excellent medium for germination because it holds moisture well and provides good drainage.
What you will need:
- Several seeds
- A shallow container
- Sand
- A spray bottle
How to test a seed’s ability to germinate using sand:
- Select a shallow container. You can use a deeper-based pot or basin if desired. However, a larger container will require more sand to fill it. Do what works for you and use what you already have lying around.
- Fill the container with a layer of sand. The sand doesn’t have to be more than 1-2 inches deep.
- Place the seeds on the sand in the container. Ensure the seeds are evenly spaced and not pressed too deeply into the sand.
- Cover the seeds with a thin layer of sand. You want the seeds to be close to the surface but still have a layer of sand over them.
- Mist the sand with a spray bottle until it’s fully saturated. Moisture is critical when it comes to germinating seeds. You will also need to regularly mist the seeds until they sprout.
- Place the container somewhere that’s warm and has plenty of light. Again, a window seal or table is a good option. The seeds need sunlight and warmth to germinate, but they also can’t get too hot or cold.
- Wait for the seeds to grow or not. During the next ten days, you will need to regularly check on your seeds and ensure they have enough water, light, and warmth. Eventually, if the seeds are viable, they will pop up.
Once the seeds grow, you can easily transplant them into your garden, where they will thrive. However, if they don’t end up sprouting, you’ll know the seeds aren’t viable and have put in a lot of work. Unfortunately, testing seeds is the best way to ensure they’ll grow.
Conclusion
Testing old seeds for germination is possible and easy, depending on the effort you’re willing to put in. Floating seeds are a great option if you’re looking for a quick test. However, germinating seeds is the only surefire to tell if a seed is viable. Plus, once the seeds sprout, you can easily plant them in your garden.
