Test Last Year’s Seeds Before You Sow

Old seeds can still grow—sometimes beautifully. But climate stress (hotter garages, humid basements, heat waves during shipping) shortens seed life and makes germination patchy. Before you commit trays, soil, and water, run a simple viability test and adjust your sowing plan.

Why seed viability drops faster now

Seeds age faster when they’re stored warm or damp. Aim for cool and dry: around 4–10°C (39–50°F) and <50% relative humidity if possible. A common rule is that temperature (°F) + humidity (%) should be under 100 for long storage.

Watch for these red flags:

• Packets stored in a shed/garage that hit >27°C (80°F)
• Condensation inside jars or zip bags
• Musty smell, clumping, or visible mold

The paper-towel germination test (most reliable)

1. Count out 10 seeds (or 20 for a better sample).
2. Moisten a paper towel until damp—not dripping.
3. Spread seeds, fold, and seal in a labeled zip bag (leave a little air).
4. Keep warm at the crop’s typical range: 20–24°C (68–75°F) works for many vegetables.
5. Check daily. Add a few drops of water if the towel is drying.
6. Stop when most viable seeds would have sprouted—usually 5–10 days for fast crops (lettuce, brassicas), 10–14 days for slower ones (peppers, parsley).

Germination % = (sprouted ÷ total) × 100.

How to interpret your results

• 80–100%: Sow normally.
• 60–79%: Sow thicker or plant extra cells/row length.
• 40–59%: Consider replacing, or pre-sprout and transplant only vigorous seedlings.
• <40%: Compost them or use only if seed is rare—expect gaps.

Tip: “Sprouted” means the radicle (tiny root) is visible, not just a swollen seed.

Quick field checks (useful, but imperfect)

• Soak test: Some floaters still germinate; don’t discard solely on floating.
• Cut test: For large seeds (beans, squash), slice one. A healthy seed is firm and pale, not shriveled or darkened.

Climate-smart steps to improve success

If viability is moderate, you can still get a good stand:

• Pre-sprout on towel, then plant only sprouted seeds.
• Keep seed-starting mix at steady moisture; avoid dry-downs during heat spikes.
• For many crops, use heat wisely: warm soil speeds germination, but >30°C (86°F) can stall cool-season seeds (like lettuce).

Store leftovers for next season

Dry seeds thoroughly, seal with a desiccant packet, and store in the fridge. Label with year, variety, and any notes from your test—your future self will thank you.