1. Record the number of seeds you planted at day 0.
2. Record the number of seeds that germinated at day n.
3. Write a fraction that compares the number of seeds that germinated to the number of seeds that were planted.
4. Show each fraction as a percentage.
5. Express the percentage as a rate.
For example, if you planted 50 radish seeds and 35 seeds germinated after 37 days, you would write 35/50 = 70/100 = 70%. The germination rate is 70% at or after day 37 or c. 1 seed germinating per day, etc.
You can define it how ever you like, so long as you express it as an actual 'rate' i.e. number or % per day or after a certain time period :)
Rate is taken as an amount at a given time it is not a speed, but as any relative proportion is subject to angular transformation in order to keep normal distribution, see arcin()