Viability Testing

Part of Seed Saving

Before planting season, you need to know if your stored seeds will actually grow. Viability testing tells you which seed lots are still good, which need higher seeding rates, and which should be replaced entirely.

Seeds do not last forever. Every year in storage, a percentage of seeds lose the ability to germinate. Environmental conditions, seed age, species characteristics, and storage quality all affect how quickly viability declines. Testing before planting prevents the disaster of sowing dead seeds and losing an entire growing season.

Why Seeds Lose Viability

Seeds are living organisms in suspended animation. Even in dormancy, metabolic processes continue at extremely slow rates. Over time, cellular membranes break down, DNA accumulates damage, and stored food reserves degrade. Three factors accelerate this decline:

Moisture: Seeds stored at high moisture content respire faster, consuming their food reserves and generating heat that causes further damage. Seeds above 14% moisture can even support fungal growth that destroys them from within.

Temperature: Every 10°F (5.5°C) increase in storage temperature roughly halves seed longevity. Seeds stored in a hot attic may last one year. The same seeds in a cool basement might last five years.

Oxygen: Oxidative damage accumulates over time. Seeds stored in sealed containers with reduced oxygen last significantly longer than those stored in paper envelopes exposed to air.

The Seed Storage Rule of Thumb

Temperature (°F) + relative humidity (%) should equal less than 100 for good storage conditions. For example: 60°F + 35% RH = 95 (good). 80°F + 60% RH = 140 (seeds will deteriorate rapidly).

Expected Seed Longevity by Crop

Before testing, know what to expect. Some seeds naturally last much longer than others.

Crop	Expected Viability (Years)	Notes
Onion, parsnip, parsley	1-2	Notoriously short-lived; test every year
Corn, pepper, spinach	2-3	Replace frequently
Bean, pea, carrot, lettuce	3-4	Moderate storage life
Tomato, brassicas, beet	4-6	Good keepers in dry storage
Cucumber, melon, squash	5-8	Among the longest-lived vegetable seeds
Wheat, rice, barley	3-10	Highly variable by storage conditions
Lotus (Nelumbo)	100+	Exceptional case; not relevant to food crops

These figures assume reasonably good storage conditions (cool, dry, dark). Seeds stored in hot or humid conditions will lose viability much faster.

The Water Float Test

The simplest test, though also the least reliable. Drop seeds into a container of room-temperature water and wait 15-30 minutes.

How it works: Viable seeds tend to be dense and heavy because their endosperm is intact. Dead or damaged seeds often have internal air pockets where tissue has broken down, causing them to float.

Procedure:

1. Fill a bowl or jar with room-temperature water
2. Drop in 20-50 seeds
3. Wait 15-30 minutes (not longer — even good seeds absorb water and eventually sink)
4. Seeds that float are likely non-viable; seeds that sink are likely good

Limitations of the Float Test

This test has a high false-positive rate. Many perfectly viable seeds float because of natural air pockets in their seed coat (especially squash family seeds). Some dead seeds sink because their coat is intact even though the embryo is dead. Use this test only as a rough first screening, never as your sole viability assessment.

Best used for: Large seeds like beans, peas, corn, sunflower. Less useful for small seeds like lettuce, carrot, and brassicas.

The Cut Test

A quick visual assessment that tells you about seed fill and embryo condition, though it destroys the tested seeds.

Procedure:

1. Select 10 representative seeds from your lot
2. Cut each seed in half lengthwise with a sharp knife or razor blade
3. Examine the interior

What to look for:

Observation	Interpretation
Firm, white or cream-colored embryo fills the seed	Likely viable
Embryo is plump and fills the entire cavity	Good endosperm reserves
Embryo is shrunken, gray, or brown	Likely dead or dying
Interior is hollow or powdery	Dead seed, possibly insect-damaged
Visible mold or discoloration inside	Fungal contamination, not viable

Cut Test for Grain Seeds

For wheat, corn, and other grains, the cut test is particularly informative. A healthy wheat kernel shows a glassy, translucent endosperm when cut. A dead or weathered kernel looks chalky and opaque. This difference is easy to spot even without magnification.

The Germination Test

This is the gold standard for viability testing. It directly measures what you care about — will these seeds actually sprout?

Standard Germination Test Procedure

Materials needed:

• Paper towels, cloth, or cotton batting
• A plate, tray, or plastic bag
• Water
• A warm location (65-80°F / 18-27°C for most crops)

Steps:

1. Count out exactly 10, 20, or 50 seeds (use a number that makes percentage calculation easy)
2. Moisten a paper towel or cloth — damp, not dripping
3. Spread seeds on one half of the towel, spaced so they do not touch
4. Fold the other half over the seeds
5. Place in a plastic bag or on a plate (to retain moisture)
6. Put in a warm location out of direct sunlight
7. Check daily. Add water if the towel begins to dry
8. Count germinated seeds (radical/root tip visible = germinated)
9. Continue checking until no new germination occurs for 3 consecutive days

Interpreting Results

Germination Rate	Action
90-100%	Excellent. Plant at normal seeding rates
70-89%	Good. Increase seeding rate by 20-30%
50-69%	Marginal. Double your seeding rate or blend with fresh seed
25-49%	Poor. Use only if no alternative; plant very thickly
Below 25%	Replace this seed lot entirely

Test Timing

Run germination tests 4-6 weeks before planting season. This gives you time to source replacement seed if your stored stock has declined. Testing the day before planting is too late to act on bad results.

Germination Test Timing by Crop

Different crops take different amounts of time to germinate, even under ideal conditions:

Crop	Days to Germination	Test Duration
Radish, lettuce, brassicas	2-5	7-10 days
Beans, peas, corn	3-7	10-14 days
Tomato, pepper, eggplant	5-10	14-21 days
Carrot, parsley, celery	7-21	21-28 days
Onion	7-14	14-21 days

Be patient with slow-germinating species. Calling a test early will undercount viable seeds.

Tetrazolium Staining Test

A chemical test that reveals living tissue within hours rather than days. Tetrazolium chloride (2,3,5-triphenyltetrazolium chloride, TTC) is a colorless chemical that living cells convert to a red dye called formazan. Dead tissue remains unstained.

Procedure:

1. Soak seeds in water for 12-24 hours to fully hydrate them
2. Cut seeds in half to expose the embryo (or puncture the seed coat for small seeds)
3. Prepare a 1% TTC solution (1 gram TTC dissolved in 100 ml water)
4. Place cut seeds in the solution
5. Incubate at 85-95°F (30-35°C) in darkness for 2-6 hours
6. Examine seeds — living tissue stains red/pink, dead tissue stays white or brown

Acquiring Tetrazolium

TTC is available from chemical supply companies and some agricultural suppliers. In a post-collapse scenario, this test may not be available. Learn the germination test method as your primary testing approach and consider TTC a useful tool if the chemical is accessible.

Reading Tetrazolium Results

The location and extent of staining matters as much as whether staining occurs:

• Fully stained embryo — Viable, strong seed
• Embryo stained except for radicle tip — May germinate but produce weak seedlings
• Only cotyledons stained, embryonic axis unstained — Not viable
• Patchy staining with dead zones — Reduced vigor, may not germinate
• No staining — Dead seed

This test is faster than germination testing (hours vs. days) and is useful when you need quick answers. However, it requires some practice to interpret correctly and does not tell you about seed vigor — only whether the tissue is alive or dead.

Practical Testing Strategy

For a subsistence-level operation where every seed counts, follow this systematic approach:

Annual Testing Calendar

1. Late winter (6 weeks before planting): Test all seed lots more than one year old using the germination test
2. Test in batches: Group seeds by expected planting date and test the earliest-planted crops first
3. Record results: Keep a seed inventory with germination percentages and test dates
4. Make decisions: Order or trade for replacement seeds while there is still time

Record-Keeping Format

Maintain a simple seed log:

Variety	Harvest Year	Test Date	Seeds Tested	Germinated	Rate (%)	Action
Cherokee Purple Tomato	2024	Feb 2026	20	18	90%	Plant normally
Blue Lake Bean	2023	Feb 2026	50	31	62%	Double seeding rate
Yellow Onion	2025	Feb 2026	20	5	25%	Replace

One Test Is Not Enough

A single germination test tells you the rate at one moment in time. Seeds continue to decline in storage. If you test at 70% in February and do not plant until May, the rate may have dropped further — especially if storage conditions are poor. For critical crops, test again closer to planting if your first test showed marginal results.

Adjusting Seeding Rates

Once you know your germination rate, adjust how many seeds you plant to ensure adequate plant stands:

Formula: Seeds needed = (Desired plants) / (Germination rate as decimal)

Example: You want 100 tomato plants and your germination test showed 75% viability. 100 / 0.75 = 134 seeds needed

For direct-seeded crops (planted directly in the ground), also factor in field emergence, which is typically 10-20% lower than lab germination rates due to soil conditions, pests, and weather.

Field-adjusted formula: Seeds needed = (Desired plants) / (Germination rate x 0.85)

Example: You want 200 corn plants, germination is 80%, field factor is 85%. 200 / (0.80 x 0.85) = 200 / 0.68 = 295 seeds needed

Quick Reference: When to Replace Seed Stock

Replace your seed stock when:

• Germination falls below 50% for any crop
• Seeds are past their expected longevity (see table above)
• Seeds show visible mold, insect damage, or musty smell
• Seeds feel lightweight or hollow compared to fresh seed
• You cannot test and the seeds are more than 2 years old for short-lived species

Key Takeaways

Viability testing is essential insurance against planting dead seeds. The germination test (seeds on damp paper towel, count sprouts over 7-21 days) is the most reliable method available without laboratory equipment. Test all stored seeds 4-6 weeks before planting so you have time to source replacements. Expect different lifespans from different crops — onion seeds rarely last past 2 years, while squash seeds can remain viable for 8 years or more. Record your results, adjust your seeding rates based on germination percentage, and never gamble a growing season on untested seed stock. When in doubt, plant thick and thin later.