DETERMINING THE DURATION OF THE JUVENILE PHASE OF COREOPSIS-GRANDIFLORA (HOGG EX SWEET.), GAILLARDIA X GRANDIFLORA (VAN-HOUTTE), HEUCHERA-SANGUINEA (ENGELM.) AND RUDBECKIA-FULGIDA (AIT.)

The juvenile phase of Coreopsis grandiflora 'Sunray', Gaillardia x gra ndiflora 'Goblin', Heuchera sanguinea 'Bressingham', and Rudbeckia ful gida 'Goldsturm' was characterized by exposing plants with 0 to 20 nod es to cold treatments at 5 degrees C. After 0, 10, or 15 weeks cold tr eatment, plants were grown at constant 20 degrees C under a 9 h photop eriod with 4 h night-interruption lighting (22:00 to 02:00 h; long day s) or under a 9 h photoperiod (short days), Based on flowering percent age and time to flower, we concluded that the juvenile phase of Coreop sis, Gaillardia, Heuchera, and Rudbeckia ended when they had approxima tely 8, 16, 19, and 10 nodes, respectively. Coreopsis required cold tr eatments to flower. A cold treatment was not required for flowering of Gaillardia and Rudbeckia; however, such treatment improved their flow ering percentage and greatly accelerated flowering. Increasing cold du ration from 10 to 15 weeks did not influence time to flower of Coreops is, Gaillardia, and Rudbeckia; however, the increase enhanced flowerin g percentage of Coreopsis and Gaillardia and hastened flowering of Heu chera. Heuchera was a day-neutral plant after ten weeks cold treatment , Rudbeckia was an obligate long-day plant, and Gaillardia and Coreops is were quantitative long-day plants. (C) 1998 Elsevier Science B.V.