Seed storage life adjuster

What this calculator does

Published viability figures usually assume seed kept cool and dry — something like a cool room and low humidity. Real cupboards are often warmer and damper than that, and seed ages far faster than the packet table suggests. This tool applies a simple rule of thumb: seed life roughly doubles for every 10°C drop in temperature, and for every 15% drop in relative humidity, and shortens by the same logic when conditions get warmer and wetter.

When to use it

• Deciding whether a warm kitchen cupboard is ruining your seed.
• Comparing a sealed jar in a cool room with an open packet on a shelf.
• Judging how long saved seed might realistically last in your home.

How to use it

1. Pick a crop to set the baseline, or type your own figure from a viability table.
2. Estimate your storage conditions. A typical room is around 20°C; humidity varies with climate and season.
3. Read the adjusted life and treat it as an estimate, not a measurement.

Worked example

Take tomato seed with a baseline of about five years in cool, dry conditions. Kept at a warm 25°C and 60% humidity, the model cuts the expected life to well under two years. Move that same jar to a cool 5°C and 30% humidity, and the full five years returns — which is why the fridge, kept dry, is such an effective store.

Limitations

• It is a simplified model, not a lab test. Real seed lots differ widely, and the doubling rules break down at extremes.
• It assumes dry seed. Sealing damp seed into a cold jar traps moisture and can be worse than leaving it out.
• Freezing is not automatically better. Only thoroughly dried seed tolerates it; otherwise condensation ruins the seed.

Frequently asked questions

Related guides

• How to keep seeds dry in storage
• How long do seeds last?
• Desiccant amount calculator