Flowering in Crimson Clover as Affected by Planting Date.

Understanding factors that affect flowering of crimson clover (Trifolium incarnatum L.) could improve management decisions to optimize utilization by improving season of use. The experiment was a split-plot randomized complete block design with three replications at College Station, TX, in the 1997-1998 and 1999-2000 growing seasons, and Overton, TX, in the 1998-1999 growing season. Main plot treatments of two crimson clover cultivars and subplot treatments of six planting dates (PDs) were used to evaluate the effect of date to reach 50% budding and 50% flowering based on day of year (DOY), days after planting (DAP), photothermal index (PTI), and growing degree days (GDD) under field conditions. Correlations with 50% bud and 50% flower were almost identical. 'Columbus' planted in the autumn flowered an average of 49 d later than 'Tibbee'. Date to reach 50% flowering was best correlated with DOY (r = 0.93 and 0.97) and DAP (r = 0.92 and 0.98) for Columbus and Tibbee. Date to reach flowering was not as highly correlated with PTI (r = 0.66 and 0.82) or GDD (r = 0.71 and 0.85) for Columbus and Tibbee, thus temperature could not be used to predict flowering. Planting after 21 December delayed flowering in Tibbee 2 to 9 wks, whereas, Columbus planted after 21 December did not flower. It is important to plant early in the growing season or to use later-maturing cultivars to maximize the length of the growing season and possible total production in grazed environments.