Seed Germination Calculator

Work backwards from your last frost date. Most vegetables need 4 to 10 weeks of indoor growing before they can be transplanted outdoors. Add the germination period (typically 3 to 21 days depending on species) to the transplant lead time to find the indoor start date. For example, tomatoes need 6 to 8 weeks of grow time plus 5 to 10 days to germinate, so start 7 to 9 weeks before last frost.

Fast germinators (3 to 7 days at optimum temperature): radish, lettuce, cucumber, squash. Moderate (7 to 14 days): tomato, pepper, basil, corn, beans. Slow (14 to 21 days): celery, parsley, parsnip, carrot, most perennial flowers. Some species like parsley and carrot can take up to 28 days. Temperature and seed freshness significantly affect actual germination time.

Most vegetable seeds germinate best at soil temperatures of 65 to 75 degrees F (18 to 24 degrees C). Warm-season crops like tomatoes, peppers, and cucumbers germinate fastest at 75 to 85 degrees F (24 to 29 degrees C) and very slowly below 60 degrees F. Cool-season crops like spinach and lettuce germinate well at 40 to 75 degrees F. Use a seedling heat mat if your starting location is cool.

Germination rate is the percentage of seeds that successfully sprout. USDA Federal Seed Act regulations require minimum germination rates on seed packets (e.g., 80% for tomatoes). If you plant 100 seeds with an 80% germination rate, expect approximately 80 seedlings. Always plant 20 to 25% more seeds than needed to account for germination variability.

Perform a germination test: place 10 seeds on a moist paper towel, fold and seal in a plastic bag, keep at 70 to 75 degrees F, and count how many germinate after the expected germination period. If 7 of 10 germinate, germination rate is 70%. Seeds stored correctly (cool, dark, dry) remain viable for 1 to 5 years depending on species. USDA seed storage research finds tomato seeds viable for 4 to 5 years; onions only 1 to 2 years.