Interactive lesson

Storing seed, step by step

Interactive lesson: from harvest to jar — drying in the shade, silica gel, cleaning, packing, protection from weevils and mice, and the germination test.

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The whole lesson as text

1. How seed ages

Seed in a drawer isn't dead: it breathes slowly, uses up its food reserve and ages.

Seed is alive — The same tomato seed loses its germination in two or three years in a warm, steamy kitchen. In a dry jar somewhere cool it still germinates after ten.
The 1 % moisture rule — For every 1 % less moisture in the seed (between 5 and 14 %), its life roughly doubles.
The 5 °C rule — For every 5 °C lower temperature (between 0 and 50 °C), the life doubles too. A cool place for jars is 5–15 °C (41–59 °F).
Jar before cellar — Seed moisture follows air humidity. Dry seed in a packet in a damp cellar or shed soaks up moisture within a few weeks, so a closed jar matters more than a cold place.

Why: How fast it ages depends on two things: how damp it is and how warm it is. Most seed isn't lost in the garden but in the cupboard.

Seed of onions, parsley and parsnips lives 1–2 years. Renew it every year.
Damp seed is ruined in the freezer: the water freezes and destroys it. Only well-dried seed in a jar goes into the fridge or freezer.

2. Drying

Freshly extracted seed contains 20–50 % moisture.

Shade and a draught — A covered porch or a room with an open window. On a plate, a sieve, baking paper or a cloth.
No more than 35 °C — Never on a baking tray in the oven, on metal sheeting or on a radiator. In the sun on metal or concrete, seed overheats within an hour.
A thin layer — A layer one seed thick; stir twice a day for the first few days. A small fan halves the drying time. Don't dry tomato or cucumber seed on kitchen roll, because it sticks.
The snap test — Small seed takes 1–2 weeks, large seed 2–4. Dry seed snaps or cracks rather than bending: a hammer blow shatters a bean rather than squashing it. Only then does it go into a jar.

Why: In the first days it needs drying fast enough not to go mouldy, but gently enough not to cook it. Slowly, in the shade, in moving air.

A loft under the tiles can get too hot in summer, and in a damp autumn a dry room indoors is often the best place.
Direct sun only in the morning, briefly.