COLD TREATMENTS, PHOTOPERIOD, AND FORCING TEMPERATURE INFLUENCE FLOWERING OF LAVANDULA-ANGUSTIFOLIA

The influence of cold treatments and photoperiod on flowering of 8- to 11-node and 18- to 23-node Lavandula angustifolia Mill. 'Munstead' pl ants from 128-cell (10-mL cell volume; P1) and 50-cell (85-mL cell vol ume; P2) trays, respectively, was determined. Plants were stored at 5 degrees C for 0, 5, 10, or 15 weeks, then forced under a 9-h photoperi od (SD), or under a 4-h night-interruption (NI) (2200 to 0200 HR) phot operiod at 20 degrees C. Percentage of plants flowering, time to flowe r, and plant appearance were evaluated. Increasing duration of cold tr eatment was associated with an increase in flowering percentage in pla nts from both cell sizes, More plants flowered under NI than SD except in P2 cooled for 15 weeks, where all plants flowered, Average time to visible bud (VB) and to opening of the first flower (FLW) generally d ecreased with increasing duration of cold treatment. Inflorescence cou nt in P2 plants increased with increasing duration of cold treatment. To determine the relationship between forcing temperature and time to flower in L. angustifolia 'Munstead', three sizes of plants were expos ed to 5 degrees C for 13 weeks and then forced under a 4-h NI (2200 to 0200 HR) at 15, 18, 21, 24, or 27 degrees C. Plants generally flowere d more quickly at higher temperatures, time to FLW decreasing from 77, 71, and 60 days at approximate to 15.6 degrees C to 46, 40, and 36 da ys at approximate to 26 degrees C for P1, P2, and 5.5-cm (190-mL pot v olume) (P3) plants, respectively. Generally, P1 plants flowered 5 to 1 0 days later than P2, and P2 flowered 5 to 10 days later than P3.