Seed Viability Chart: How Long Seeds Last

Seed viability chart: years by crop

Two university tables agree on most vegetables. The first is a University of Nebraska-Lincoln Extension guide to seed storage and germination, which calls its numbers relative longevity. The second is a University of Illinois Extension seed viability sheet, which calls them approximate seed life.

The two tables share 34 crops. On 31 of them they give the same number of years, and the table below groups those 31 by years.

Read the number as a planning guide. A packet inside its years should sprout well. A packet at or past them needs a test before you count on it.

Seed loses vigor long before it loses the ability to sprout.

Where the tables disagree

Leek, lettuce and tomato get different numbers from different universities. A third source, a University of Wisconsin-Madison Extension page on testing seed viability, adds a split on spinach.

Leek is the widest gap, at 4 years. When tables disagree, use the shorter number to decide when to test, and the longer one as the most you can hope for.

Test a packet with 10 seeds and a paper towel

A germination test settles what a chart cannot. Illinois Extension gives the method. Put 10 seeds on a damp paper towel, fold it, and seal it in a plastic bag or container so it stays moist. Keep it in a warm place, and count the sprouts after the number of days on the seed packet. Sunlight is not needed.

The Nebraska guide tests bigger samples. It uses 25 or 50 seeds at 70 to 75 degrees F and takes the final count at two to three weeks. It also says seed lots with lowered germination can still be planted at higher rates than usual.

The universities disagree on the bottom of the scale. Six sprouts out of 10 means buy new seed on the Illinois sheet. The Wisconsin page says that 5 out of 10 is still plantable, as long as you sow more seeds, and that a rate under 40 percent is better replaced.

If a packet holds the only seed of a variety you cannot buy again, use the Wisconsin cut-off and sow thickly. If it holds ordinary seed, use the Illinois one. The Seed-Starting Countdown has a page for the test count and the sums that follow.

What the sprout count tells you to sow

Turn the count into a share, then divide the number of plants you want by that share. This is arithmetic, not a university figure, and it assumes the same share sprouts in your bed.

Round up, and thin the extras once the seedlings are up. Seed vigor starts to drop before the sprouting rate does, the Illinois sheet warns, so the few seeds that do sprout from a weak lot may give weaker plants.

Keep seed dry and cool to get the full years

Both universities say the same thing about storage. The Nebraska guide says longer life comes from keeping seeds dry and at low temperatures. The Illinois sheet says to store seed below 45 degrees F in a sealed jar or bag, in a refrigerator if you have room. It adds that the container should reach room temperature before you open it.

Wet or warm storage cuts the years. If seeds sprout in storage, the Illinois sheet says, they will not grow when planted the next year.

How old a seed can get

A packet in a drawer is not the record. A 2008 report in Science describes a date palm seed from Masada that was radiocarbon-dated to the first century CE and then germinated. The authors say Dead Sea climate may have helped it last, and call it the oldest directly dated viable seed.

A 2012 study in the Proceedings of the National Academy of Sciences went further back. Researchers regrew a flowering plant, Silene stenophylla, from fruit tissue radiocarbon-dated to 31,800 years, found in permafrost at 38 meters deep. They grew it by tissue culture, so it was not a sown seed. These are rare cases of sealed, frozen or desert-dry storage, and none of them tells you about a packet in a shed.

When a free chart is all you need

If you grow a handful of crops and keep a few packets, the two tables above are plenty. Write the years on a sticky note and test the doubtful packets once a spring. A free printable list does the same job if it has a column for the year.

The Seed-Starting Countdown helps if you want the seed year, the test result and the sow count in one place, printed beside your planting dates. It does not tell you a seed's age. That comes from the year you wrote on the packet.

Its dates count from your own last-frost date, and every kit holds a table of last and first freeze dates (10, 50 and 90 percent) for 108 NOAA stations, from the 1991 to 2020 normals, so it is not tied to one zone. The inventory page takes the packet years in winter, the test page takes the count before you sow, and the weekly log pages from 14 weeks before frost take the sowing dates. For a printed seed list, test page and planting countdown, The Seed-Starting Countdown is the file to open.