Seed germinated between 2 and 32◦C with the optimum germination temperature at 16–17◦C. Heat shock temperatures (35–40◦C) of less than 50 h duration reduced germination (at 16◦C) below 50%. At 45◦C, 100% seed lethality was induced within 24 h of heattreatment. Accordingly, calendula seed should be sown in the field only if forecasted soil conditions are expected to be below 30◦C during seed germination