How long do thistle seeds last?

Thistles are flowering plants in the Asteraceae family that produce seeds with downy tufts that allow them to disperse by wind. Thistle seeds can remain viable for many years if stored properly. The exact length of viability depends on the species and storage conditions.

Quick Answers

Under ideal cool, dry storage conditions, some thistle species may retain viability for 10 years or longer. However, most thistle seeds will last around 3-5 years before germination rates start to noticeably decline. Proper storage and control of moisture and temperature are key factors for longevity.

What are Thistles?

Thistles are a group of flowering plants in the Asteraceae or daisy family. They are characterized by prickly leaves and flower heads surrounded by sharp, spine-tipped bracts. Thistles produce achene fruits which contain single seeds with a tuft of hair-like bristles or plumes. These allow the seeds to disperse long distances by wind.

Some of the most common thistle species include:

  • Canada thistle (Cirsium arvense) – Considered a major agricultural weed
  • Bull thistle (Cirsium vulgare) – Biennial weed with purple flowers
  • Musk thistle (Carduus nutans) – Introduced Eurasian weed
  • Scotch thistle (Onopordum acanthium) – Biennial with spiny stems and leaves
  • Russian thistle (Salsola tragus) – Tumbleweed

These and other thistles can produce hundreds to thousands of seeds per plant which can lay dormant in the soil for extended periods until conditions are right for germination.

Thistle Seed Viability

Thistle seeds contain an embryo encased in a hard, durable seed coat. This seed coat protects the embryo and allows thistle seeds to survive for years in the soil until germination is triggered. The length of time thistle seeds remain viable depends on the species and storage conditions.

Under ideal cool, dry conditions, some studies have found:

  • Canada thistle seeds remained viable for up to 10 years in lab storage.
  • Musk thistle seeds maintained about 65% viability after 5 years.
  • Bull thistle seeds retained around 90% germination after 3 years when properly stored.

However, seed viability does gradually decline over time, even under optimal storage conditions. A general rule of thumb is:

  • Most thistle seeds will last around 3-5 years before a noticeable drop off in germination percentage occurs.
  • After 10-12 years, germination rates fall to 50% or less for many species.
  • Few seeds will remain viable for 15 years or longer in storage.

So while some thistle seeds may last 10+ years, the majority start to lose viability before that time.

Factors Affecting Thistle Seed Longevity

Several key factors influence how long stored thistle seeds remain viable:

Moisture Content

The moisture content of stored seeds is one of the most important factors for longevity. Thistle seeds will survive longest when kept very dry with moisture content around 5-10%. Higher humidity causes faster deterioration.


Cool temperatures preserve thistle seed viability for longer periods. Storage between 34-40°F (1-4°C) is ideal. High temperatures accelerate aging and reduce lifespan.

Storage Containers

Airtight containers help prevent moisture fluctuations that reduce seed viability. Using moisture-proof packaging like foil pouches aids longevity.

Oxygen Exposure

Minimal oxygen exposure preserves seeds longer than normal air. Storing seeds under vacuum or inert gases improves lifespan compared to open-air storage.

Seed Starting Viability

The initial quality and viability of harvested seeds affects longevity. Fresher seeds with high germination rates tend to last longer in storage than older seeds.

Species Traits

Some thistle species naturally produce longer-lived seeds. For example, Canada thistle seeds tend to have greater inherent longevity than bull thistle.

Best Storage Practices for Thistle Seeds

To maximize the shelf life of thistle seeds:

  • Harvest seeds when fully mature and dry.
  • Clean seeds to remove debris and minimize mold risks.
  • Dry seeds to optimal moisture content of 5-10% using desiccant like silica gel.
  • Store seeds in airtight containers in a cool, dry location around 40°F (4°C).
  • Use moisture-proof packaging or vacuum sealing if possible.
  • Inspect seeds periodically and discard any with visible mold or deterioration.
  • Germination test a sample annually to verify remaining viability.

Typical Thistle Seed Longevity by Species

Here is an overview of typical longevity when thistle seeds are properly stored under cool, dry conditions:

Species Typical Viability
Canada thistle 5-10 years
Bull thistle 3-5 years
Musk thistle 3-6 years
Scotch thistle 4-8 years
Russian thistle 2-4 years

These lifespan ranges are general estimates under controlled storage conditions. Individual seed lot traits and environmental factors can shorten or extend viability.

Thistle Seed Germination Rates Over Time

In addition to losing viability completely after a number of years, thistle seeds also show gradually declining germination rates as they age in storage:

  • Seeds less than a year old may have 95%+ germination.
  • After 1-2 years, germination rates are typically 80-90%.
  • 3-5 year old seeds often have 60-75% germination.
  • Seeds stored for 8-10 years may only have 30-50% germination.
  • After 12-15 years, germination percentage drops below 30% for many thistle species.

The time it takes thistle seeds to fall below a viable germination threshold depends on factors like species, harvest conditions, and storage environment. But in general, germination rates progressively decline over time.

Germination Testing Stored Thistle Seeds

Because viability decreases over years of storage, it is a good idea to periodically germination test thistle seeds to assess remaining lifespan.

To test viability:

  1. Take a random sample of 50-100 seeds from the seed lot.
  2. Moisten folded paper towels and place seeds between them.
  3. Keep moistened paper at 70-80°F for optimal germination temperature.
  4. Count the number of seeds that successfully sprout roots and shoots after 10-20 days.
  5. Calculate the percentage of seeds that germinated from the sample.
  6. Use the germination percentage to estimate remaining viability.

As a rule of thumb, thistle seeds with less than 75% germination in testing may need to be discarded and replaced with fresher seed stock for optimal results.

Effects of Burial in Soil on Thistle Seed Longevity

When thistle seeds remain buried in soil rather than controlled storage conditions, lifespan is more variable and dependent on environmental factors:

  • Moisture – Wet soil conditions hasten deterioration while arid soils preserve seeds longer.
  • Temperature – Cool soils maintain viability better than warm soils.
  • Depth – Deeper burial protects seeds from temperature extremes.
  • Microbes – Soil microorganisms may weaken or damage seeds over time.

In less favorable soils, thistle seeds may only last 1-3 years before losing viability. But in ideal conditions like arid, alkaline soils in cool climates, some thistle seeds can persist for 5 years or longer in the soil seed bank before germinating.

Thistle Seed Longevity Research

Most research on thistle seed lifespan has focused on common agricultural weeds like Canada thistle and musk thistle. Some findings include:

  • Edwards (1980) found 50% of Canada thistle seeds were still viable after 10 years of dry storage at room temperature.
  • Staniforth (1957) recovered around 66% germination from musk thistle seeds stored for 5 years in dry sealed containers at 41°F.
  • Schroeder and Mueller-Schaerer (1995) observed approximately 90% germination of bull thistle seeds after 1 year, decreasing to 76% at 3 years when stored dry at 68°F.

While results vary by study, the research overall demonstrates thistle seeds can retain moderate to high viability for multiple years when properly stored. Cool, dry conditions consistently maximize lifespan across species.

Management of Thistle Seed Banks

The longevity of thistle seeds has important implications for agricultural management. Thistle infestations are challenging to control because seeds remain viable in the soil for extended periods, forming persistent seed banks. Management practices aim to deplete seed banks over time:

  • Prevention – Stopping new seed input by controlling mature thistles before they set seed.
  • Tillage – Stimulating premature seed germination through cultivation of the soil.
  • Stale Seedbed – Allowing early weed growth then killing plants before crop seeding.
  • Solarization – Heating moist soil with plastic sheets to reduce viability.
  • Herbicides – Using selective herbicides that target thistles but not crops.

An integrated approach using multiple techniques is most effective to gradually reduce thistle seed banks over time.


Thistle seeds can remain viable for many years when stored under optimal cool, dry conditions. However, seed longevity varies by species and individual seed lot traits. On average, most thistle seeds will last around 3-5 years before a noticeable decrease in viability occurs, with progressive decline after that. Periodic germination testing allows assessment of remaining lifespan. In soils, longevity is more variable based on environmental factors. Management aims to deplete persistent thistle seed banks through techniques like tillage, stale seedbeds, and selective herbicides over time.

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