Testing the germination rate (viability) of seeds before planting is a good idea, especially if the seeds are old, or if you collected them yourself. If the seeds don’t germinate well, you won’t waste time sowing and caring for seeds that don’t have much chance of growing.
So, how do you test seed germination rate? The best way to test seed germination rate is to sow the seeds in warm, loose, moist soil and give them time to germinate. If the seeds do not sprout within a couple of weeks, then they may be no good. If they do sprout, you can calculate the germination rate by dividing sprouted seeds by total seeds planted, and multiplying by 100.
For example, if you plant 10 seeds and 3 of them sprout, then your germination rate is 100*(3 / 10), or 30%. Older seeds tend to have a lower germination rate than newer seeds.
When germinating seeds, you do need to be careful with factors such as soil temperature, moisture, and air circulation. If the soil is too cold (or too warm), then you may get a low germination rate. In reality, the seeds are not bad, but rather the temperature is to blame.
Let’s take a closer look at how to test seed germination rate and the factors that affect seed germination. Then we’ll talk about how to use the seed germination rate to decide how many seeds to plant.
How To Test Seed Germination Rate (Seed Viability Test)
When testing to find seed germination rates, it is important to give the seeds the proper environment to grow. If the soil temperature, moisture, or consistency is off, then you might end up throwing away seeds that could have grown well given the right conditions.
Let’s start off with how to prepare the soil for seed germination.
Prepare The Soil For Seed Germination
When doing a seed germination test, it is best to do it indoors so that you can control the temperature and moisture levels in the soil.
A potting soil mix will work fine for this purpose, but you can also use some soil from your garden if you want.
The soil should be loose, meaning that it has not been compacted in any way. Do not press down hard on the soil before or after planting seeds!
Seeds and seedling roots need air circulation, since oxygen in the soil is necessary for plants to survive.
The soil should also be moist, since seedlings need to absorb some water in order to germinate properly. Dry soil will not do, but you also want to avoid soaking wet soil, since this can prevent air circulation or cause the seeds to rot.
When the soil is prepared, you are ready for the next step: preparing the environment for germination.
Prepare The Indoor Environment For Seed Germination
After you have prepared your soil, you will want to make sure that the temperature is ideal for germination. The ideal temperature for seed germination varies widely by plant.
For example, the minimum temperature for cold-weather crops such as lettuce is 32 degrees Fahrenheit (0 degrees Celsius). On the other hand, the minimum temperature for warm-weather crops such as peppers is 60 degrees Fahrenheit (15.6 degrees Celsius).
For more detailed information, check out these tables from the University of California, which give minimum, maximum, and ideal temperature ranges, along with times for seed germination at various temperatures.
As you can see from the first table, the ideal temperature for seed germination depends on the plant. However, you cannot go wrong with a temperature of 75 degrees Fahrenheit (23.4 degrees Celsius).
Keep in mind that these temperatures refer to soil temperature, rather than air temperature. Also, keep in mind that a temperature far above or below the ideal range can cause a big change in germination time.
For instance, based on the second table, cucumber seeds will germinate in 4 days at 77 degrees Fahrenheit, but they will take 13 days at 59 degrees Fahrenheit.
To achieve the ideal temperature, you can set the thermostat in your house accordingly. However, 75 degrees Fahrenheit may be too warm (or too expensive!) for some people (including me).
One solution is to use an electric space heater (perhaps an infrared heater) to warm up the space where your seeds are growing. However, the electricity costs can still add up when using a space heater.
Another possibility is to use a heating mat below the seed tray to warm up the soil. That way, you aren’t paying to warm up the entire room (or the entire house).
You can also use overhead lights to warm up the soil slightly. Most seeds do not need light to germinate, but seedlings will need light after they emerge, so it pays to set up a grow light ahead of time.
Some seeds, like onions, may even be inhibited by light. However, there are some seeds that do need light to germinate, including Begonia and Coleus.
For more information, check out this article on seeds and seedlings from the Penn State University Extension.
Prepare The Seeds For Germination
Now that the soil and environment are ready for planting, it’ time to prepare the seeds themselves!
Before you do anything else, make sure to label any seeds, containers, and trays as necessary, to avoid any confusion later on. This is especially important if you are doing a germination test for multiple different types of seeds.
You can simply plant the seeds in the soil when the soil is ready, but there are a couple of ways to speed up germination.
One way to speed up germination is to soak the seeds before planting them. Usually, you do not need to soak seeds for longer than 24 hours (even less for some) before planting.
Another way to speed up germination is to scarify the seeds. This means using a knife or fingernail clippers to scratch the surface of hard seeds, to allow water to get in more easily.
Once the seeds are ready, count them out and record the number somewhere where you will not lose it. Then, plant the seeds in the soil that you prepared earlier.
Now, you will have to wait for the seedlings to emerge!
Wait For Seed Germination
This is the boring part – you need to wait several days for the seeds to germinate. Hopefully, the seedlings will all start poking up out of the soil at around the same time.
The time to germination will depend on the plant, and also on the soil temperature. If you are not sure how long to wait, check out the second table in this document from the University of California.
You can give the seeds a few days longer than the tables indicate, but eventually, you will need to conclude that the seeds are too old to germinate properly.
This can happen if the seeds are too old, since germination rates decline over time. For more information, check out my article on how long seeds last.
If your seeds to germinate and seedlings start to emerge, then you are in luck! Now you can calculate your seed germination rate and make plans for this year’s garden planting.
Calculate Seed Germination Rate
Now that your seeds have had enough time and have begun to germinate, it is time to calculate the seed germination rate.
To do this, first count the number of seedlings (sprouts) that you see – that is, the number of seeds that germinated properly.
Then, divide by the number of seeds that you planted in the soil.
Finally, multiply by 100, and this will give you the seed germination rate as a percentage.
For example, let’s say that you planted 20 tomato seeds. Ten days later, you count 16 seedlings, which means that 16 seeds germinated out of 20 planted.
We calculate 16/20 = 0.8, and then multiply by 100 to find an 80% germination rate.
This suggests that 80% of the seeds we plant will germinate under ideal conditions. However, keep in mind that this germination rate is under ideal conditions.
When planting seeds outdoors, you won’t be able to control the temperature. However, you can prepare the soil in your garden and keep it moist by watering.
You can also wait until after the last frost to plant your seeds. This will prevent damage to your seeds (while they are germinating) or to seedlings (after they emerge).
Use Seed Germination Rate To Determine How Many Seeds To Plant
Now that you know the seed germination rate for the packet of seeds, you can figure out how many seeds to plant.
Let’s say that you want 20 tomato plants for your garden this year. If the seed germination rate is 80%, then you would actually need to plant 25 seeds, since 80% of 25 is 20.
The calculation goes like this: take the number of plants you want, multiply by 100, and then divide by the seed germination rate.
For example, if you want 30 tomato plants and have a seed germination rate of 60%, then you should plant (30*100) / 60 = 3000 / 60 = 50 seeds. You can check the math: 60% of 50 is 30, since 0.6*50 = 30.
If you are worried about conditions outdoors being less than ideal for seed germination, then either use a lower germination rate (such as 50% instead of 60%), or plant a few extra seeds as “insurance”.
If you end up with extra seedlings, you can always give them to friends or family who have a garden and are willing to adopt the plants!
Do You Need To Soak Seeds Before Planting?
As mentioned earlier, you can soak seeds before planting to speed up the germination process. However, you don’t have to soak the seeds, since it is not necessary for germination to occur.
What is necessary is that the seeds are able to absorb enough water to germinate. Whether you soak the seeds or not, you will need to make sure the soil is moist enough so that the seeds can absorb water.
Can You Germinate Seeds In A Paper Towel?
Yes, you can germinate seeds in a paper towel. The paper towel holds moisture and allows the seeds to breathe, serving as an alternative growing medium.
To germinate seeds on a paper towel, wet the paper towel until it is damp (not soaking wet). Then, lay out the seeds so that they are separated (not touching).
Keep the paper towel and seeds in a warm place, to encourage faster germination and higher germination rates. Remember, you cannot go wrong with a temperature of 75 degrees Fahrenheit (23.9 degrees Celsius).
The only drawback of this method is that you will need to transplant the sprouted seeds into soil by hand, since they will soon need nutrients from the soil to grow and establish stronger roots. Be gentle when handling the tiny sprouted seedlings!
Germinating seeds in a paper towel may be helpful if you live in an area with a short growing season.
By now, you know how to test seed germination rates, and you also have a better sense of the factors that affect seed germination.
If you are saving seeds, remember that seeds from hybrid plants may not grow true to type. You can learn more about hybrid seeds in my article here.
I hope that you found this article helpful – if so, please share it with someone who can use the information.