Test Old Seeds Before Planting Them

By Michael Chen · October 8, 2026

Seeds Do Not Last Forever

Seed viability declines over time. Some seeds remain viable for 5+ years (tomatoes, cucumbers), while others lose vigor within 1-2 years (onions, parsnips, parsley). Before ordering new seeds, test your leftover packets — you might save money and still get great germination.

The Paper Towel Test

Place 10 seeds on a damp paper towel, fold it, and put it in a sealed plastic bag. Keep at room temperature (70-75°F). Check daily for germination. Most seeds sprout within 5-14 days. Count how many of the 10 germinated to calculate your germination rate.

Interpreting Results

80%+ germination: plant at normal spacing. 50-79%: plant seeds more thickly and thin later. Below 50%: order fresh seeds. Seeds with low germination rates also tend to have less vigor — seedlings may be weaker and slower growing even if they do sprout.

Seed Longevity by Crop

Short-lived (1-2 years): onions, parsnips, parsley, leeks, sweet corn, spinach. Medium (3-4 years): beans, peas, carrots, lettuce, peppers. Long-lived (5+ years): tomatoes, cucumbers, squash, melons, radishes, beets, brassicas. Flower seeds vary widely — zinnia and marigold last 3-5 years, aster and delphinium only 1-2 years.

Storage Conditions Matter

Seeds stored in cool, dry conditions last longer. Ideal storage is 40°F and 30% relative humidity — a sealed jar with silica gel packets in the refrigerator works well. Seeds stored in hot garages or humid basements lose viability much faster than the averages above.

When to Buy Fresh

Always buy fresh seed for short-lived crops regardless of how carefully you stored them. For expensive or rare varieties, test germination 4 weeks before your planting date so you have time to order replacements if needed.