Photoperiod and cooling duration influence growth and flowering of six herbaceous perennials

Seedlings of six taxa of herbaceous perennials were subjected to 0, 4, 8 or 12 weeks cold treatment at 2-3 degrees C followed by long or short day pho toperiods after the cold treatment. Cold was not necessary for flowering in any taxa studied, but the duration of cold treatment was inversely related to forcing-phase days to Bower for all taxa. Plant height at flowering inc reased due to cooling in Myosotis scorpioides (forget-me not) and Campanula carpatica (Carpathian harebell) while decreasing in Anchusa capensis (Cape bugloss). In M. scorpioides, the number of growing points also decreased a s cooling duration increased. Photoperiod influenced flowering time in four taxa but not in M. scorpioides and Arabis blepharophylla (fringed rock-cre ss). Flower stems of M. scorpioides and A. capensis elongated more in long days than in short days. Short days reduced internode elongation in Gypsoph ila repens (creeping baby's breath) and inhibited flowering of C. carpatica and Catananche caerulea (blue Cupid's dart). Taxa were classified as day n eutral, quantitative long day, or qualitative long day plants.