P&PDL Picture of the Week for
September 13, 2010

Heat Delay in Garden Mums due to High Night Temperatures

Roberto G. Lopez, Ph.D., Assistant Professor & Floriculture Extension Specialist, Purdue University

Natural flower initiation in garden mums occurs in late July when daylengths (photoperiod) are shorter than earlier in the season. Mums are often categorized as early-, mid-, and late-season cultivars, with respect to flowering.  Research at Kansas State University has shown that flower bud initiation is also influenced by temperature and is most sensitive during the first 2 weeks of short days.  High night temperatures, such as those experienced during the summer of 2010, have contributed to “heat delay” or delayed flowering (Figure 1). This year, many growers are finding that garden mum cultivars that typically are marketable in mid-September are delayed by 1 to 3 weeks (Figure 2). 

In addition, uneven flowering (Figures 3 and 4), flower bud deformation, irregular floret arrangements or crown buds (Figure 5) can also be associated with high temperatures during flower initiation and/or development.  Sensitivity to high temperatures is cultivar dependent.

Click image to enlarge

Delayed flowering in mums

Figure 1

Delayed flowering in mums

Figure 2

Uneven flowering in mums

Figure 3

Irregular floret arrangements in mums

Figure 4

Irregular floret arrangements in mums

Figure 5

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service