Evaluation of cardinal temperature for three species of medicinal plants, Ajowan (Trachyspermum ammi), Fennel (Foeniculum vulgare) and Dill (Anethum graveolens)

In order to evaluate cardinal temperatures and optimum thermal range of germination of three medicinal plants including Ajowan, Fennel and Dill an experiment was conducted in a Completely Randomized Design with three replications. Temperatures considered for this study were: 5, 10, 15, 20, 25, 30 and 35 ?C. Results indicated that temperature affected germination rate and percentage of these crops. Optimum thermal range for Ajowan and Fennel seeds were determined as 10-20 ?C and 10?C for Dill. The basic optimum and maximum temperatures were 2.88, 20 and 38.35 for Ajowan, 3.86, 20 and 34.98 for Fennel and 5, 13 and 33.7 for Dill. In general, as it is expected, germination response of these crops to temperature was correlated with the nature of growth of these plants. At higher temperatures, Dill as a winter crop showed a lower germination percentage compared to Ajowan and Fennel.