The Effect of Vernalization and Photoperiod on Flowering of Tall Bearded Irises1,2

Abstract

Abstract Two varieties of tall bearded iris, ‘Color Carnival’ and ‘First Violet’, were grown at minimum temperatures above 20° F throughout the fall and winter months. Groups of these plants were transferred periodically to a 65° house where they received either long or short-day treatments. Plants of ‘Color Carnival’ flowered under long days, regardless of the length of the vernalization period; under short days, some flowering occurred if the plants received more than 8 weeks of vernalization. Plants receiving 16 or more weeks of vernalization flowered equally well under long days or short days. Plants of ‘First Violet’ did not flower under flowering did not occur until the plants had long days unless the plants had received 16 or more weeks of vernalization; under short days received 20 or more weeks of vernalization. The longer the plants had been held at the minimum temperature, the shorter the time required for flowering after being transferred to 65°.