The two parents of a hybrid combination differ in their growth duration and therefore flower at different times even when sown on the same date. To produce hybrid seed successfully on a commercial scale, male and female parents planted side by side in a fixed row ratio should flower simultaneously, which is called synchronization. Synchronized flowering between two parental lines of different growth duration can be achieved by seeding them on different dates which is termed seeding interval (SI). The method of arriving at an SI using growth duration is simple to practice. In this method, the difference between parental lines in the number of days to initial heading or 50% flowering from seeding is used to determine SI.