Seed is cleaned by the route that matches how it grows: dry-seeded crops are threshed, winnowed and screened to remove pods, chaff and trash, while wet-seeded crops such as tomato and cucumber are fermented or washed free of pulp and then dried completely. Clean seed stores longer because trash holds moisture and shelters insects and mould.
Part of Community Seed Bank Management
Seed cleaning separates viable seed from pods, chaff, pulp and debris and leaves it dry enough for storage.
Two Routes: Dry Processing And Wet Processing
Dry processing (beans, peas, grains, lettuce, brassicas, herbs):
- Thresh to break seed from pods or heads: flail on a clean sheet, trample in a sack, or rub heads by hand.
- Winnow by pouring seed from one container to another in a gentle wind, or by fanning, so that light chaff blows away and heavy seed falls.
- Screen through a coarse mesh that holds back pod pieces and a fine mesh that lets dust and tiny seed through.
- Finish drying in a thin layer before the container.
Details are in Dry Seed Processing.
Wet processing (tomato, cucumber, squash, melon, pepper):
- Tomato and cucumber: scoop seed and pulp into a jar with a little water and leave it loosely covered for 2-3 days, stirring daily. A skin of mould on top is normal. Fermentation dissolves the gel coat that inhibits germination and can destroy some seed-borne disease. Viable seed sinks; pour off the floating pulp and light seed, rinse, and dry on a plate. Floating is a guide, not a proof: a germination test settles it (Germination Rate Testing Protocol).
- Squash, melon and pepper: scoop, wash off the pulp, and dry. No fermentation is needed. See Washing Seeds.
Do not dry wet-processed seed in direct sun on a hot surface or near a fire; high heat kills the embryo. Spread it thin on paper or a screen in warm shade with air moving across it. Wet seed left in a heap sprouts or moulds within days.
Match The Method To The Seed
| Crop type | Typical method | Watch for |
|---|---|---|
| Beans, peas | Shell by hand or trample dry pods | Cracked seed coats; split seed does not store |
| Wheat, oats, barley | Thresh, winnow, screen | Weed seed of similar size; pick it out |
| Corn | Shell from dry cobs | Mould between kernels; discard it |
| Lettuce, herbs | Shake into bag, rub, screen | Fine dust; winnow gently |
| Brassicas | Thresh pods in a bag, screen | Pods open on their own; work over a sheet |
| Tomato, cucumber | Ferment 2-3 days, rinse, dry | Seed stuck together after drying; break it apart |
| Squash, melon, pepper | Wash, dry | Seed dried too fast or too hot |
Seed Can Carry Disease
Some diseases ride on or in seed. Clean seed lots from healthy plants only, discard seed from plants that were visibly diseased, and read Sanitation and Quarantine Protocols for heat treatment of seed lots.
Weighing Before And After Shows How Much Seed A Crop Yields
Cleaning loses weight. Weigh the harvest before and after cleaning and record both. If 2.0 kg of threshed beans comes out of 3.0 kg of pods-and-seed, the cleaned seed is 2.0 ÷ 3.0 = 67% of the raw weight. Use your own figure to plan how many plants to grow for a seed lot.
Common Mistakes
- Storing seed with chaff. Trash holds water and feeds insects.
- Washing dry-seeded crops. Beans, peas, corn and grains are threshed, not washed.
- Drying wet seed in a heap. Spread it in a single thin layer.
- Mixing two varieties on one sheet. One stray seed becomes a contamination; clean one variety at a time and wipe the surface between.
What’s Next
- Learn next: Storage Conditions — drying and holding the cleaned seed
- Combine with: Seed Inventory and Catalog System — labelling the lot immediately