If you want to be sure your seeds will grow, it’s worthwhile to do a germination test first to confirm they are viable (will sprout) and find out the expected germination rate. This is particularly valuable for older flower and vegetable seeds we’ve had sitting in storage for a few years or longer.
For seed starting instructions also see Seed Starting For Beginners: Sow Inside Grow Outside which shares all of my tips for indoor seed sowing.
Good Reasons To Test Seeds
If you have ever sown a bunch of flower or vegetable seeds in the garden or containers only to watch and wait for weeks to find nothing sprouted, it’s a big disappointment and a lot of valuable growing time wasted.
For those of us in cold climates, those days between last frost in spring and first frost in fall are prime growing days and not to be squandered on bad seeds.
Viability: the ability of seeds to germinate
Most seeds stay viable for at least a year. From there, it varies greatly.
We know a lot about the best way to store seeds at home but you can never really know if they are viable unless you try growing them.
Germination: the beginning of growth of a seed, spore, or bud
While it is an extra step, a germination test takes out the guesswork.
Not only will you learn whether or not the seeds will sprout, but you can also find out your germination rate. This tells you what percentage of your seeds are viable, which in turn lets you know how many to sow to end up with the quantity of plants you want.
How long does it take to test seeds?
How long a germination test takes depends on the type of seed. You can’t hurry a seed to sprout but you can provide optimum conditions which ensure it happens as soon as possible.
The test is done at home and does not require soil or other growing medium, just household supplies.
For most seeds you’ll have an answer in 10-14 days. On the quick end, radishes sprout within days, while peppers can take weeks, and something like clematis can take a year or more.
I like to test most seeds in early spring, a number of weeks before last frost, so I have answers before it’s time to direct sow crops outdoors.
This way, if I’ve got some duds, there is still time to order fresh seeds.
You may have heard of the seed float test, which sounds very quick and easy, but unfortunately it’s not reliable. You can read more about it in the Frequently Asked Questions section.
Of all the testing methods suggested online, the paper towel method is the easiest and most reliable. I’ve provided complete step-by-step instructions below.
How To Test Seeds
- Place 10 seeds on moistened paper towel (but not dripping wet) in an open container in a dark, warm cupboard for the expected number of days to germinate (or a bit longer).
- Monitor seeds daily for changes and moisten paper towel as needed.
For seed tests, just like regular seed sowing, you will need to follow the advice on your seed packet regarding any necessary preparations. If you’re new to sowing, this article on how to read seed packets is helpful.
Dormant: not active or growing, but having the ability to be active at a later time
Dormant seeds start growing when their conditions change.
For many seeds this means taking the dry, viable seeds from storage and exposing them to moisture, warmth, and oxygen. Most do not require light until they have sprouted.
Some seeds have additional needs prior to germination that will be noted on the seed packet.
- Scarification means you need to nick the seed coat to allow water and oxygen to reach the embryo inside. Generally this is done with a nail file or sandpaper—just enough to make the coat penetrable without causing any other damage. Soaking seeds in water is another approach.
- Stratification is where we expose the seeds to cold and (usually) moisture to mimic winter conditions the plant has evolved with.
But, as mentioned, most seeds are ready to test right out of the packet.
If your seeds do sprout during the test, you can continue growing them if you like.
- Paper towel (or paper coffee filter or cotton tea towel)
- Container (food storage container, glass, or plastic) or plastic food bag
- Marking pen (or some way of labelling your test)
- Plant water mister
- Heat mat with thermostat (optional)
- If you want to test several types of seeds at once, use a separate paper towel for each group.
- Always wash your hands before handling seeds and seed sowing supplies.
- Do any required preparations listed on your seed packet like scarification or stratification prior to your test.
1. Label the container (or bag) with the name of the seeds or keep notes.
2. Moisten a sheet of paper towel with warm water (room temperature or warmer). The paper towel should be moist but not drip water when squeezed in a ball.
3. Place at least 10 seeds on one half of the paper towel. If the seeds are tiny, you may find it easier to use tweezers or the moistened tip of a dibber to set them in place.
4. Fold over the paper towel to cover seeds and place everything in an open food storage container or bag (allowing for air circulation). Make sure the moisture is reaching the entire exterior of the seeds.
5. Place your container in dark, warm cupboard or similar location.
Check your seed packet for the expected number of days to germinate so you know how long this should take. Allow extra time if conditions are not optimum.
Optimum Germination Temperatures
For this germination test, it’s ideal if your container is within this recommended temperature range.
If you have one, a heat mat with a thermostat can be used to obtain the desired temperature.
Otherwise, room temperature around 70°F (21°C) should be fine. It just means seeds like peppers, tomatoes, or zinnias that prefer warmer start temperatures may germinate a little slower than expected.
A lot of instructions say to put the seeds on top of your fridge or on a heater. I don’t recommend either of these because modern fridges tend not to get warm up top (and it may be drafty up there) and heaters can dry out the paper towel which will stop the germination process.
6. Set a reminder in your phone or calendar to check your seeds every day or two. Your job is to make sure the paper towel never gets dry. You can spritz it with warm water as needed, always making sure the seeds are kept moist.
7. After days or weeks, depending on the type of seeds and temperature, you may start seeing signs of sprouting. Some seeds within the same batch may start sooner than others. This is yet another smart survival tactic. Take pictures to compare your seeds one day to the next.
What do sprouting seeds look like?
There are so many different seed sizes, shapes, colors, and textures that no two types look the same.
If you check daily, you may notice the seed first seems to swell. It may also split open or a little bit of growth—perhaps a white root—will start peaking out from inside. But again, it’s never exactly the same twice.
Eventually, roots and shoots of some sort will appear.
Do not worry if your sprouting seeds look odd and unlike pictures you reference. They are not Frankenseeds. This is simply how seeds grow and each will be unique.
8. When you feel you have given the test enough time—at least as long as the expected number of days to germinate with some elbow room, you can do your assessment.
- Seeds sprouted = they are viable.
- How many sprouted = your germination rate.
For example, if 8 out of 10 germinated, that’s an 80% germination rate.
Because this is such a small sample size, your actual germination rate be higher or lower but you have a ballpark number.
A good sample size would be 100 seeds or more but most of us don’t want to use up that many seeds just to find out.
If you are concerned about quantities for the garden, always sow extra for insurance.
More Ways To Use This Test
You can also use this germination test to both test and grow various fruit seeds from kitchen scraps including:
I much prefer testing first so I don’t bother planting in soil unless I know the seed is viable.
Frequently Asked Questions
Yes. Depending on the time of year and what they are, the sprouted seeds could be transplanted into pots (indoors or outdoors) or planted directly outside (if conditions are suitable).
When planting, use clean hands or tweezers and handle the sprouts as minimally and carefully as possible. If the seed coat is still intact, handle that, not the roots or shoots. When planting, it’s best to bury everything just below the soil (or potting mix) surface. The plant will figure out which way is up.
You can plant the paper towel with the sprouted seed. Carefully remove any excess and plant the rest. It will eventually dissolve.
If you followed the test instructions and all of the conditions were right including adequate moisture (but not too much), warmth, and you allowed enough time for that specific type of seed yet nothing germinated, your seeds may be dead.
Any seeds known as difficult to germinate or that normally take a really long time (months or longer) may deserve more testing before writing them off. It’s always worth reading up on germination tricks to get more tips. I could never get delphinium seeds to sprout until I tried these tips.
Some really old seeds can be viable although a lot of unverified claims make the headlines. A recent verified example comes from Israel where researchers managed to grow 2000-year-old date palm seeds.
The float test is not reliable. To perform the float test, you put seeds in a cup of water to see if they sink or float. The idea is, if they have enough mass to sink, they should be viable. If they float, they’re dead.
The problem is, with all the zillions of different seed shapes, sizes, weights, and textures, this test is not reliable. Some seeds are always going to float and others are going to sink regardless of their viability. Think of carrot seeds. They are tiny and have so little mass, even the freshest seeds will float—immediately failing the test—even when they are viable. So, despite all the recommendations, don’t waste your time with this test.
- Best Soil Temperatures for Flower Seeds
- Best Soil Temperatures for Vegetable Seeds
- Seed Sowing For Beginners: Sow Inside Grow Outside
- Trick for Germinating Stubborn Delphinium Seeds
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Optimum Seed Storage
The lower the temperature and moisture levels, the longer most seeds stay viable.
Best temperature | 32-41°F (0-5°C)
Most fridges are in this range.
Also, room temperature (70°F/21°C or lower) is fine for short-term storage (1 year).
Store dry seeds and keep dry | Relative humidity below 50% | Keep away from light.
If moisture is an issue, use silica gel pack in containers.
A Weekly Indoor & Outdoor Seed Sowing Plan for Beginners
by Melissa J. Will
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~Melissa the Empress of Dirt ♛