Seed Germination of Calendula Officinalis ‘Carola' in Response to Temperature.

Calendula (Calendula officinalis ‘Carola’) is a potential agronomic oilseed crop with application in the paint, coating, and cosmetic industry. Calendula has historically been used for herbal medicinal purposes and an ornamental plant. With the discovery that calendula seeds contain high concentrations of calendic acid (C18:3) in the 1980s it began to be investigated as an oilseed crop. Understanding the optimal conditions for growth and management of calendula is necessary to incorporate the crop into agronomic rotations. The germination of calendula was optimized at temperatures from 16.5-16.8°C and was reduced both above and below this range. Above 30°C calendula germination was 0%. Heat shock temperatures (35-40°C) were shown to reduce germination (at 16°C) below 50% after exposure of less than 50h. At 45°C, 100% seed lethality was induced within 24 hours of high temperature treatment. Based on these data calendula seed should only be sown in the field if environmental temperature conditions are predicted to be below 30°C during seed germination.