The 2009 ASHS Annual Conference

Plants that did not receive any cooling but were subjected to 9 or 12 hr. photoperiods were never marketable whereas non cooled plants that received 15 hr photoperiod and NI were marketable. Plants that received no cooling, or those that received 9 and 12 hr photoperiods required more time on the bench than plants that received at least 6 weeks cooling, or 15 hr and night interruption (NI). In general, as the number of weeks of cooling increased, the amount of time on the bench decreased.   Once plants were subjected to at least 6 weeks cooling, all plants were marketable however they required less bench time as photoperiod increased.   Being cooled for greater than eight weeks had little influence on marketable time for all photoperiod treatments except 15 hr.  
     In general, plants subjected to 9 and 12 hr. photoperiod required longer bench time than those that received 15 hr. and NI, regardless of cooling duration.  If provided with a photoperiod of 15 hr or NI, plants were marketable regardless of cooling duration.
     The data suggest that Kolkwitzia must receive at least 6 weeks of cold if the photoperiod is less than 12 hr., but if subjected to long photoperiods (15 hr., NI), cooling is not required.