A field study was undertaken to optimize the sowing date under the best seed cooling degree during the tow seasons of 2012 and 2013 for Hibiscus sabdariffa L. in Ismailia, Egypt. The experiment was comprised of sowing times (April, May and June), seed cooling degree (Room, 5° and 10°) and their interactions, aiming to increased yield and better calyxes quality.
Vegetative growth characters (plant height, number of branches, root length, fresh and dry weights of leaves, stem and root), yields (number of flower/plant and dry weight of calyx/plant) and anthocyanin content were best with sowing date in April13th under of 10°C seed cooling and their interaction, during both seasons.
Conclusively, sowing of roselle at early time (13th April) and treated of seeds under 10oC was the best treatment for enchanting plant growth, yield of calyx and highest percentage of anthocyanin under sandy soil conditions .