Calculators · Post-harvest

Seed Storage Life Calculator.

By the Open Agriculture Technology Collective

What this is: Calculator
Domain: Post-harvest
Cost: Free, no account
Use: In the browser, or embed

Seed Storage Life Calculator

How long seed stays alive where you keep it, and how much longer a refrigerator or a sealed jar buys you.

Your seed and where it lives

Crop

Temperature unit

Storage temperature Where the jar or drawer sits most of the year

Humidity the seed dried at (%) Open storage: the room's humidity. Sealed jar: the humidity where it dried before sealing.

Germination now (%) From the packet or a rag-doll test

Years in storage

Hundred Rule — °F + %RH should be 100 or less

Seed moisture —% Estimated, fresh-weight basis

Versus an open shelf —× Times longer than at 70°F and 50% humidity

Germination after 3 years —% Estimate for sealed, steady storage

Years until 80% — Below this, sow more thickly

Years until 50% — Below this, replace the seed

Where to keep it

Setting	Seed moisture	Lasts, versus open shelf	Years until 50%

How to read it

Seed ages fastest when it is warm and damp. This calculator estimates how much a colder, drier spot slows that down. For seven crops with published constants it also estimates how many years your seed will take to fall to 80 percent germination, when you should start sowing more thickly, and to 50 percent, when it is time to replace it.

Open storage (an envelope in a drawer, a card catalog in a library): seed takes on the moisture of the room, so enter the room's usual humidity.
Sealed storage (a jar with a good lid): the seed keeps whatever moisture it had when you sealed it. Enter the humidity of the room where it dried, and the temperature where the jar lives. Drying seed in a dry room, or in a jar with silica gel, before sealing is the single biggest gain.
Below about 10 percent humidity there is no further benefit, and very dry seed of some crops is harmed. The calculator stops counting there.

The Hundred Rule

A rule of thumb widely credited to the UC Davis seed scientist James Harrington: storage is good when the temperature in degrees Fahrenheit plus the relative humidity in percent adds up to 100 or less. Harrington's related rules say seed life roughly doubles for every 10°F drop in temperature and every one-point drop in seed moisture, within limits. The calculator uses the more exact equation below, but the Hundred Rule is the one to remember.

The math

Seed scientists predict storage life with the Ellis and Roberts (1980) seed viability equation. Germination is converted to probits (the normal-distribution scale), and it falls in a straight line over time:

v = Ki − p / σ
log10 σ = KE − CW · log10(m) − CH · t − CQ · t²

v   germination in probits after p days;  Ki  starting germination in probits
σ   days for germination to fall by one probit
m   seed moisture, % of fresh weight;  t  storage temperature, °C
KE, CW  constants for each species
CH = 0.0329, CQ = 0.000478  temperature constants shared by all
          orthodox seed (Dickie et al. 1990)

Seed moisture comes from measured equilibrium values at 25°C for 18 vegetable and grain crops, interpolated for your humidity (Rao et al. 2006, compiling Harrington 1972 and Justice and Bass 1978). The comparison uses each crop's own moisture constant where one is published and 4.5 otherwise, the low end of the range measured across twelve crops (Ellis, Hong and Roberts 1989), so it understates rather than overstates the benefit of drying.

Crop	KE	CW	CH	CQ	Source
Lettuce	8.218	4.797	0.0489	0.000365	Kraak and Vos 1987, Annals of Botany 59
Onion	6.975	3.470	0.040	0.000428	Ellis and Roberts 1981, Seed Science and Technology 9
Pepper	7.767	4.670	0.0329	0.000478	Demir et al. 2009, HortScience 44
Southern pea (cowpea)	8.690	4.715	0.026	0.000498	Ellis, Osei-Bonsu and Roberts 1982, Annals of Botany 50
Soybean (edamame)	7.748	3.979	0.053	0.000228	Ellis, Osei-Bonsu and Roberts 1982
Chickpea	9.070	4.829	0.045	0.000324	Ellis, Osei-Bonsu and Roberts 1982
Barley	9.983	5.896	0.040	0.000428	Ellis and Roberts 1980, Annals of Botany 45

What it cannot tell you

Your seed lot. The constants come from laboratory studies of particular seed lots. Seed that was harvested wet, damaged or old before storage will do worse. Test germination before you count on an estimate.
Swinging conditions. The equation assumes steady, sealed storage. Seed that cycles between cool nights and hot afternoons ages faster than its average temperature suggests; a garage or a sunny windowsill is worse than the numbers show.
Deep freezing. The constants were tested down to about 9°F (−13°C). For a freezer the calculator uses that temperature, so read freezer results as "at least."
Tomatoes, beans, squash and most other crops have no published constants we could verify, so for them the calculator shows how much better one spot is than another, not a number of years. Our seed storage guide has typical lifespans by crop.

Free under CC BY 4.0. Cite as "Open Agriculture Technology Seed Storage Life Calculator (openagriculturetechnology.com)".