4. Conclusion
Calendula germination is optimized both in rate and cumulative percent at temperatures of 16.5–16.8◦C. As temperature increased above 17◦C, germination decreased. Furthermore, as imbibed calendula seed was exposed to heat shock temperatures, germination was unable to recover even after seed was placed at To. These results indicate that if calendula seed is planted at a relatively low soil depth as is currently recommended, followed by a period of high temperature, stand establishment likely will be affected negatively.