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Twelve-Year Shelf Life Study on
Garden Seeds Stored in a Refrigerator

Copyright © August 2, 2021 by Robert Wayne Atkins, P.E.
All Rights Reserved.


The following is Chapter Twenty-Nine in my book: The Food Book.

Introduction

For many years I have been very disappointed in the reliability of the information available in books, and on the internet, about the actual shelf life of seeds.

Before I began my seed germination experiment I did a careful internet search on this topic and I found a lot of websites that provided some summary information on the shelf life of seeds. However, as I compared the seed shelf life information from lots of different websites it became obvious to me that they were all reporting almost exactly the same information. And none of the websites provided any research data that the owner of that website had personally collected to support the information that was being reported. In other words, all I could find was the same basic generic information and that information was being reported again, and again, and again, with the only differences being the name of the website reporting the information and the way in which the information was formatted.

On the other hand, I suspect that the seed companies that package and sell seeds have an extensive database on the shelf life of the seeds they grow and sell. And I suspect that those seed companies do not share this information for the following reasons:
  1. The information is proprietary knowledge gained by the company based on their financial investment in harvesting and storing seeds and if they freely shared their information then they would forfeit whatever competitive advantage their data gave them.

  2. The demand for seeds changes from year-to-year and it is not easy to predict what the demand will be for next year, or for future years, for each type of seed.

  3. Based on their inventory of each type of seed from previous years, and their most recent germination results on those seeds, each seed company may decide to package and sell seeds from their inventory based on factors other than first-in first-out. In other words, if the seeds the company harvested in a particular year are rapidly losing their germination potential, then the company may decide to package and sell those seeds for the upcoming planting season and label those seeds as "Packaged for Planting in the Year 20xx." Those seeds may still have a reasonable germination percentage for the year in which they are sold to us, but those seeds may continue to quickly lose their ability to germinate with each passing year in storage.

  4. Or a seed company may decide to mix some of their seeds that have a low germination percentage with some seeds with a higher germination percentage so that the average germination percentage of the seeds is "reasonable" for the year in which we buy them.

  5. If a seed company told their customers approximately how long their seeds would survive in a reasonable storage environment, then their customers may save any seeds they did not plant and use those seeds in future years. This could significantly reduce the company's sales of seeds in future years, and it would make their job of forecasting demand for seeds much more difficult, and it could result in a significant loss of revenue for the company.

  6. Therefore the companies that sell seeds do not publish their true shelf life data on seeds because if they did then it would probably discredit most, or all, of the seed shelf life information that is currently published in books and on internet websites.

My Twelve-Year Shelf Life Study
on 14 Different Types of Seeds

My twelve-year seed germination experiment had the following five objectives:
  1. To determine the germination impact of storing seeds in heavy-duty zipper plastic bags in a normal home refrigerator.

  2. To determine the germination percentages of different types of seeds, such as beets and corn, over a twelve-year period.

  3. To determine if different varieties of a specific type of seed, such as Beefsteak Tomato or Roma Tomato, had better or worse germination results after several years in storage.

  4. To determine if the seeds from any of the major seed companies had better or worse seeds when their seeds were compared based on their germination percentages as time passed.

  5. To determine if presoaking seeds in water, or presoaking in a hydrogen peroxide solution, had any impact on the germination of seeds.
The table below summarizes the results of my twelve-year germination experiment on seeds.

Specific details about the different varieties of seed and the different seed companies are at the end of this chapter.

* * * * * * *

Germination Percentages for Different Types of Seeds Based on their Age
All seeds were stored in their original packages and
also inside a heavy-duty zipper freezer bag in the refrigerator at 40ºF (4.4ºC).

Age of
Seeds =
New1 Year Old2 Years Old3 Years Old4 Years Old5 Years Old6 Years Old7 Years Old8 Years Old9 Years Old10 Years Old11 Years Old12 Years OldAverage %
Beans100%88%93%97% -96%100%100%99%92%96%100%-96%
Beets97%83%91%92% 85%96%100%88%81%100%90%92%71%90%
Carrots72%77%73%73%-77%72%90%64%58%83%92%81%76%
Corn100%92%99%98%97%90%95%97%100%98%100%100%80%96%
Cucumbers96%100%100%100%100%90%92%100%100%92%100%98%-97%
Lettuce98%91%99%92%94%96%88%96%80%74%74%71%-88%
Okra96%98%96%93%89%96%96%84%88%79%85%94%95%91%
Onions80%81%73%-69%90%76%78%76%70%65%67%52%73%
Radish100%100%100%99%100%100%100%100%92%100%100%97%98%99%
Spinach57%91%46%78%77%61%52%48%57%51%64%63%-62%
Squash80%91%85%100%75%93%100%94%100%92%93%85%-91%
Tomatoes96%77%88%97%95%100%96%100%92%93%97%85%-93%
Turnips93%98%97%-100%100%100%100%100%100%81%97%82%96%
Watermelons94%96%92%91%85%-100%90%85%93%96%85%-92%
Yearly Average90%91%88%92%89%91%90%90%87%85%87%88%80%88%

The data in the above table is based on 242 different samples that contained a total of more than 9,100 seeds.
The 14 different types of seeds that were tested are listed in the left column of the above table.
The samples included 57 different varieties of seeds that were packaged and sold by 12 different seed companies.


Information About the Data in the Above Summary Table

  1. Cold Storage: All the seeds were stored in their original paper packages and also inside a heavy-duty zipper plastic bag in my home refrigerator at 40ºF (or 4.4ºC).

  2. Individual Percentages: All the percentages, except for the averages, are based on the number of seeds that germinated divided by the total number of seeds of that age and that type of vegetable.

  3. Average Percentages: The average percentages on the right of the table and at the bottom of the table are the simple averages for each of the rows and each of the columns.

  4. Different Seed Companies: There was no significant difference in the germination percentages of the seeds packaged by different seed companies.

  5. Different Varieties of the Same Type of Seed: There was no significant difference in the germination percentages of the different varieties of seeds of the same type of vegetable, such as different varieties of beans or different varieties of corn. Some of the results of 99% or 100% include tests on 2 or more different varieties of seed of the same vegetable in the same year.

  6. Presoak in Water: Although not shown in the table, presoaking some of the seeds for one-hour had no impact on the final germination percentage of the seeds. However, presoaking did result in a slightly higher germination rate during the first two days of germination but by the third or fourth day the seeds that had not been presoaked had total germination rates equivalent to the seeds that had been presoaked.
    • Immediate Planting: If you will be immediately planting the seeds in some dirt after the one-hour presoak then the presoak may quicken the growth of a few of the seeds into healthy seedlings.
    • Delayed Planting: If you intend to continue soaking the seeds until most of them germinate and then you will plant the seeds in some dirt, then a one-hour presoak will not increase the total germination rate of the seeds.

  7. Presoak in Hydrogen Peroxide: Some older seeds were presoaked in pure water and some were presoaked in hydrogen peroxide solutions of 10%, 50%, and 100% hydrogen peroxide. Although not shown in the table, hydrogen peroxide had no impact on the older seeds in these different samples.
    • The seeds that were not presoaked and the seeds that were presoaked in a 100% water solution had a final average germination rate of 78%.
    • The seeds that were presoaked in one of the three solutions that contained 10%, 50%, or 100% hydrogen peroxide had a final average germination rate of 78%.
    Based on this experiment the use of hydrogen peroxide does not change the germination rate of seeds.

  8. Low Germination Rates: Carrots, onions, and spinach consistently had lower germination percentages each year.

  9. Age of Seeds: Seed germination rates gradually declined as they aged, with a few exceptions. The germination rate of seeds can be significantly extended by storing the seeds in a normal refrigerator.

  10. Random Fluctuations: Occasionally the germination rate for a specific type of seed went down in one year and then back up the next year. A careful examination of all the original data revealed that this was due to random factors that would not consistently repeat themselves in future tests. In other words, future tests would also contain a few random exceptions but those exceptions would be for seeds of different ages and packaged by different seed companies.

  11. Final Results: The average germination percentage for all the seeds in any one year (bottom row of table) ranged from a low of 80% to a high of 92%. This suggests that seeds can be stored in heavy-duty zipper plastic bags in the refrigerator for up to 12 years and their germination percentage will only reduce a little each year. Therefore there is no reason to discard old seeds if they have been consistently stored in a humidity controlled environment (heavy-duty zipper bag) at a low temperature in the average home refrigerator.

Conclusions

  1. Seeds need to be stored in a cold environment to significantly extend their shelf life. A normal home refrigerator is perfect for seeds.

  2. Seeds should be stored in the dark. If seeds are stored inside their original paper envelope then light will not touch the seeds even when the refrigerator light is temporarily on.

  3. Seeds need to be stored in a low humidity environment so they cannot absorb moisture while they are in storage. Most of the seeds that are sold in stores are sealed inside coated paper envelopes that protect the seeds from moisture. In addition, storing packaged seeds in a heavy-duty zipper plastic bag protects the seeds and the packages from moisture inside the refrigerator.

  4. Seeds are living organizations and they need to be stored in a limited amount of atmosphere to stay alive and they should not be vacuum sealed. Storing seeds in their original packages and inside a heavy-duty zipper plastic bag achieves this objective.

The Different Seed Companies

There was no significant difference in the germination percentages of the seeds packaged by the different seed companies, or in the seeds that I harvested and dried in different years from my own vegetable garden. In other words, the germination results of the seeds sold by the different seed companies were approximately equal.

Each seed company is in a different geographical area and the weather in their specific area impacts the vitality of the seeds they harvest each year. In other words, if the weather is great in their area then the seeds they harvest that year will be strong and healthy and the seeds will retain their germination ability for a very long time. But if the weather is bad then the seeds that are harvested that year will be weak and puny and the seeds will more quickly lose whatever germination ability they have. Weather is a random variable and it impacts all the different seed companies in a unique way each year. In other words, a seed company may have great weather and great seeds one year, and bad weather and bad seeds the next year. This means that no seed company will always have the best seeds or the worst seeds to sell each year. This became obvious to me as I did my seed shelf life experiment because each seed company had some years where their seeds germinated the best but they also had some years where their seeds had the lowest germination results. Therefore I cannot recommend any seed company as being consistently better or worse than any other seed company. This variable also influenced the up and down germination rates of seeds in the different years.


Recommendation

Purchase a few seeds in the spring of each year and put the seed packages inside a heavy-duty zipper plastic bag. Write the year on the zipper bag with a permanent black marker, and then store the seeds in your refrigerator. In my opinion, this is a better option than buying pre-packaged seeds from a survival company for the following reasons:
  1. You can buy more seeds for less money when compared to the pre-packaged seed assortments sold by survival companies.

  2. You can buy the exact varieties of seed you desire, such Golden Bantam Heirloom Corn.

  3. You will know exactly what types of seeds you have, and you will how much of each seed you have in reserve for a hard times event.

  4. The seeds will not require a lot of storage space so you can keep them in the bottom compartment of your refrigerator and this will help to significantly extend their shelf life for many, many years.
If a significant hard times event occurs then having an reasonable assortment of seeds in your refrigerator will significantly increase the chances your family will survive for the following reasons:
  1. Heirloom seeds will allow you to grow food so you can continue to feed your family after all your emergency food has been eaten.

  2. Heirloom seeds will produce seeds that are identical to the original seed so you can continue to feed your family year, after year, after year. Hybrid vegetable seeds do not produce seeds that match the original vegetable.

  3. Seeds are relatively small and they weigh very little and they could be easily taken with you if you are forced to evacuate your home.

  4. You should purchase heirloom (or open pollinated) seeds from a minimum of two different seed companies each year to increase the chance of getting some very healthy seeds from at least one of those companies based on the germination % of the seeds they package and sell that particular year. In other words, if you plan to purchase a total of 20 packages of seeds, then don't purchase all 20 packages of seeds from the same seed company. Instead purchase a few packages of seeds from at least two or more different seed companies, such as American Seed, Burpee, or Ferry-Morse. (Note: Compare the gram weight of the seed packages from different seed companies to determine their true value. American Seed packages are a lot cheaper but they also contain a lot fewer seeds than the seed packages of the more expensive brands.)

  5. Dry beans, such as pinto beans, can be purchased in a one-pound plastic bag at many grocery stores for less than one dollar. If you have limited storage space in your refrigerator then open the bag and remove about 50 of the beans and put those beans in a small envelope and write the name of the beans, the source of the beans, and the year you purchased the beans on the outside of the envelope. Then include the envelope of dry beans in your heavy-duty plastic zipper bag with the seeds you purchased from different seed companies, such as Ferry-Morse.

Additional Details about the Seeds in this Experiment

The seeds that were tested in this experiment were purchased from Walmart, Home Depot, Lowe's, Ace Hardware, dollar stores, and internet websites.

The seeds were packaged by the following seed companies: American Seed, Burpee, Ferry-Morse, Great Value (dry beans), Knoxville Seeds, Laura Lynn (dry beans), Livingston, NK Lawn & Garden, Sand Mountain, Seed Saver's Exchange, Select (dry beans), and Southern Charm. In addition, I occasionally harvested, dried, labeled, and stored seeds that I grew in my own vegetable garden. Some of my dried seeds were included in this experiment. I did not detect any significant difference between the shelf lives of my seeds when compared to the seeds of the same variety that were packaged by the major seed companies.

The different varieties of seeds that were tested in this experiment were:
  1. Beans: Black (or Turtle), Great Northern, Kidney, Lima, Navy, and Pinto.
  2. Beets: Detroit Dark Red, Ruby Queen, Sugar.
  3. Carrots: Chantenay Red Cored, Chantenay Royal, Danvers 126, Danvers Half Long, Little Finger, Scarlet Nantes.
  4. Corn: Golden Bantam, Early Golden Bantam, Reid's Yellow Dent, Stowell's Evergreen White.
  5. Cucumbers: Marketplace, Muncher, National Pickling, Poinsett, Straight Eight, Tendergreen.
  6. Lettuce: Black Seeded Simpson, Great Lakes, Iceberg, Romaine.
  7. Okra: Clemson Spineless.
  8. Onions: Cebola Texas Grano 502, Evergreen Bunching, Southport White Globe, Sweet Spanish Yellow Utah Jumbo, White Lisbon Bunching.
  9. Radish: Black Spanish, Cherry Belle, Sparkler, White Globe.
  10. Spinach: Bloomsdale Long Standing, Giant Noble, Satin.
  11. Squash: Burgess Buttercup, Dark Green Zucchini, Early Bush Scallop, Early Yellow Straightneck, Table Queen, Waltham Butternut.
  12. Tomatoes: Beefsteak, Golden Queen, Large Red Cherry, Roma, Roma VF.
  13. Turnip: Golden Ball, Purple Top White Globe.
  14. Watermelons: Crimson Sweet, Sugar Baby.

Grandpappy's e-mail address is: RobertWayneAtkins@hotmail.com

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