Germination rate calculator
Test a handful of seeds, count the ones that sprout and enter the numbers. The calculator gives the germination rate and how many seeds to sow to end up with the plants you want, optionally allowing for seedlings that die after sprouting.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter how many seeds you tested and how many sprouted.
- Enter how many plants you want.
- Optionally lower the survival percentage to allow for losses after sprouting.
How it works
Germination rate = sprouted ÷ tested × 100. Seeds to sow = plants wanted ÷ (rate × survival), rounded up.
Worked example
You test 20 seeds and 16 sprout: 80%. For 24 plants you need 24 ÷ 0.8 = 30 seeds, 6 more than the plants wanted.
Tips
- Old seed germinates less well; test seed kept for more than a season.
- Real soil is harsher than a paper towel, so the outdoor rate is often lower than the test: lower the survival setting.
- Sowing extra and thinning later is common for small seeds.
Frequently asked questions
How do I test germination?
Put 10 or 20 seeds on a damp paper towel, seal it in a bag and keep it warm. Count how many sprout over the time the packet gives, and enter that number. A bigger sample gives a more reliable rate.
How is the number of seeds to sow worked out?
Plants wanted divided by the germination rate and by the survival rate, rounded up. If 80% of seeds sprout and every seedling lives, you need 25 seeds for 20 plants.
What does the survival setting do?
It covers seedlings lost after sprouting, such as damping off or thinning. Leave it at 100% if you only want to allow for seeds that never sprout.
What if no seeds sprouted?
The rate is 0%, so no number of seeds can be worked out. The seeds may be too old, the test too cold or too dry; repeat it under better conditions.