Seed Viability Tests: Float, Fold, and 10-Seed Germination Trials

Why test seed viability at all?

Every saved or leftover seed is a tiny investment of time, space, and hope. Testing viability before sowing lets you adjust your planting density, avoid empty rows, and decide when it may be kinder to your soil—and your schedule—to start with fresher seed instead.Source - extension.illinois.edu

Extension horticulture educators often suggest that if a small germination test shows less than about seven of ten seeds sprouting, many gardeners consider moving on to a new packet rather than rely on patchy results.Source - ces.ncsu.edu

“A simple paper towel germination test gives home gardeners a realistic snapshot of how their seed lots are performing without special equipment.” – Dr. Charlotte Glen, Horticulture Agent, NC Cooperative Extension

What the float, fold, and 10‑seed tests actually tell you

The three methods overlap but serve slightly different purposes.

• Float test – offers a rough first impression for some larger seeds only.Source - blog.smartgardener.comSource - empressofdirt.net
• Fold (paper towel) test – more reliable germination snapshot for many common vegetables and flowers.Source - ces.ncsu.eduSource - extension.illinois.edu
• 10‑seed germination trial – a specific, easy‑to‑remember version of the fold test that converts directly into a percentage.

Many gardeners start with a float test on a few seeds, then confirm with a 10‑seed fold test before scaling up.

Simple framework: check, test, then decide

Here is a lightweight framework you can reuse for any seed stash:

• Step 1 – Visual check: look for obvious damage, mold, or moisture problems.
• Step 2 – Quick float test (optional): for larger seeds, as an early screen only.
• Step 3 – 10‑seed fold test: run a paper towel germination test and count sprouts.
• Step 4 – Adjust sowing plan: sow normally, sow thicker, or retire the packet.

Float test for seed viability

The float test is fast and satisfying, but it has important caveats many gardeners overlook.

How to do the float test

• Fill a clear glass or jar with room‑temperature water.
• Drop in a small handful of seeds, gently stir, and wait around 15 minutes.Source - blog.smartgardener.com
• Observe which seeds sink and which remain floating or bobbing at the surface.

Some gardeners consider sinking seeds more likely to be viable and floating seeds more suspect because they may be hollow or poorly filled.Source - blog.smartgardener.com

Limits of the float test

Seed experts caution that the float test is not consistently reliable across species. Tiny or very light seeds, such as carrots, often float even when they are perfectly viable, while some non‑viable seeds may still sink due to remaining density.Source - empressofdirt.net

Because of this, many experienced growers use the float test only as a quick curiosity check, never as their only decision tool.

Fold test: paper towel germination

The fold test—sometimes called the paper towel or baggie test—is more informative and still easy to do in a kitchen or greenhouse corner.

How to set up a 10‑seed fold test

• Moisten a paper towel so it is damp but not dripping.Source - ces.ncsu.edu
• Place 10 seeds in a row on the towel, spaced slightly apart.Source - extension.illinois.edu
• Fold or roll the towel around the seeds and slide it into a labeled plastic bag.Source - ces.ncsu.edu
• Seal the bag to hold in moisture, then place it in a warm spot (roughly room temperature or slightly warmer).

Extension guides note that for many common vegetables and flowers, checking after about one to one‑and‑a‑half weeks is usually long enough to see most sprouts.Source - ces.ncsu.edu

Checking and counting sprouts

• Start peeking after around a week by gently unrolling the towel.
• Count how many of the ten seeds have visible roots or shoots.
• Calculate germination rate: each sprouted seed equals roughly ten percent.Source - extension.illinois.edu

For example, if eight of ten seeds sprout, you have about an eighty percent germination rate. If only three germinate, germination is about thirty percent, and sowing heavily or replacing the packet may be wiser.Source - ces.ncsu.edu

Interpreting your 10‑seed germination trial

Once your test is done, you can use some simple rules of thumb to plan your plantings.

• About 9–10 of 10 seeds sprouted: sow normally; seed is performing well.
• About 7–8 of 10 sprouted: sow a little thicker or closer than usual.Source - extension.illinois.edu
• Fewer than 7 sprouted: many gardeners consider buying or saving fresher seed instead.Source - ces.ncsu.edu

Some gardeners keep a simple notebook: crop name, approximate age of seed, and observed germination percentage. Over time, that log becomes a powerful local reference for how long different seeds stay vigorous in your storage conditions.

Tips and common mistakes

These small refinements can make your tests more realistic and less frustrating.

• Match conditions to the crop. Warm‑season crops prefer warmth; cool‑season crops tolerate cooler spots.
• Don’t let towels dry out. If the towel dries, even viable seeds may stall.
• Label carefully. Especially when you test several varieties at once.
• Watch for mold. A little surface mold on towels is common; discard seeds with strong odor or obvious rot.
• Use enough seeds. Ten is a minimum; more seeds give a clearer picture when possible.Source - empressofdirt.net

Remember that a small test only estimates the behavior of the whole packet. The actual germination in your beds may end up somewhat higher or lower, so many people sow a bit extra for insurance.Source - empressofdirt.net

Who should NOT use these methods as their only guide

• Growers managing legally regulated or certified seed lots that require formal laboratory testing.
• People producing seed commercially, who may need standardized tests such as tetrazolium staining.Source - ars.usda.gov
• Anyone relying on exact germination figures for research trials or official reporting.
• Gardeners testing very rare or irreplaceable seed, where losing even a few seeds in trials feels too risky.

Bringing it all together for a sustainable seed stash

Used together, float checks, fold tests, and 10‑seed trials help you respect both your time and your seeds. You may choose to float‑test a few, run a fold test before each main sowing season, and record the results so your seed collection becomes more resilient and intentional year after year.

Many people find that this small ritual—soaking, folding, checking—turns seed organization from guesswork into a calm, almost meditative part of sustainable living.

FAQ: Seed viability tests

Can I plant seeds after a paper towel test?

Often, yes. If roots are short, you may gently move each sprouted seed into soil, keeping the root tip intact. Handle them carefully and plant promptly so the roots do not dry out.

How long should I wait before declaring seeds “dead”?

Many home tests run for about one to two weeks, but always consider the typical germination time for that crop. Some species are naturally slower and may need additional days.

Do some crops lose viability faster?

Yes. Some species naturally hold viability longer in storage than others. Storing seeds in a cool, dry, stable environment generally slows decline in many vegetable and flower seeds.Source - empressofdirt.net

Is the float test ever enough on its own?

For most home gardeners, relying on the float test alone may be misleading, especially with small or lightweight seeds. Many people treat it as a quick curiosity check and confirm with a simple germination trial.

How many seeds should I test?

Ten seeds give an easy, rough estimate. If you have plenty of seed and want a more precise number, you may test more, understanding that every seed used for testing is one you won’t be sowing.