By Brian Cantin, Senior Grower Advisor<\/em><\/p>\n Pinching poinsettias can often become so routine that one forgets\u00a0several important prerequisites to the process :<\/strong><\/p>\n Calculate\u00a0the ideal moment to pinch relative to the start of short days so\u00a0the desired number of leaves (appropriate for the pot size) have\u00a0time to develop.<\/p>\n Pinching techniques are described as a hard or soft pinch. A hard\u00a0pinch involves removal of several leaves and the growing point. This\u00a0type of pinch tends to produce rapid breaks of even length.<\/strong> Using this technique results in fewer problems with dominant shoots. A soft\u00a0pinch, where only the growing tip is removed, tends to produce breaks\u00a0more slowly due to the apical dominance effect of the immature leaves\u00a0left on the established cutting. If for some reason a soft pinch is carried\u00a0out, then leaves should also be removed to produce more uniform\u00a0breaking action.\u00a0The number of flowers per pot is dictated by how many nodes (leaves)\u00a0are left on the stem after pinch. One must take into consideration that\u00a0the lowest one or two nodes may not contribute to a full complement\u00a0of bracts at the time of flowering. On the other hand, leaving too many\u00a0nodes (i.e., more than 7 or 8) results in too many branches and\u00a0stem breakage when the plants are sleeved and shipped.<\/p>\n Stressful conditions before and after\u00a0pinch \u2013 such as high temperatures, high\u00a0light and low humidity \u2013 can be detrimental\u00a0to the development of breaks.\u00a0Misting the plants, providing shade\u00a0and wetting down floors (if feasible\u00a0in your greenhouses), are recommended\u00a0to prevent post-pinch stress. Post-pinch fertilization coincides\u00a0with a phase of rapid growth.<\/strong> In the\u00a0past, poinsettias have been considered\u00a0a high fertility crop. In my opinion,\u00a0light-leaf cultivars do indeed fit into this\u00a0category; however, the newer dark-leaf\u00a0cultivars are very efficient in their utilization\u00a0of nitrogen and require lower nutrient levels.\u00a0Thus, in general, light-leaf varieties require\u00a0more nitrogen than dark-leaf varieties. Success\u00a0with poinsettias relies on raising the initial fertility\u00a0quickly, then knowing when to taper the fertility towards the end of the\u00a0crop. Each phase of growth will dictate the optimal ratio of nitrate-N to\u00a0ammonium-N to achieve rapid vegetative growth, floral initiation and\u00a0post-harvest quality. It is important to be pro-active and monitor pH and\u00a0soluble salts on a regular basis to avoid jeopardizing the crop. Calcium\u00a0and magnesium should be monitored by media analysis, because they\u00a0are both very important nutrients in poinsettia production.<\/p>\n The rate of poinsettia growth is primarily influenced by the average\u00a0daily temperature. Modulating temperature can be used to determine\u00a0the number of leaves unfolded per week, providing a better idea of\u00a0how many leaves will unfold overall and the corresponding number\u00a0of internodes that will become part of your height control program.\u00a0When feasible, try to keep night temperatures in the low 70\u2019s until three\u00a0weeks after pinch.<\/strong> This creates sturdy, compact growth with stronger\u00a0branches.<\/p>\n Monitoring and managing leaf internode length should begin immediately\u00a0after pinch. Allowing the first and second internodes to stretch will\u00a0result in weaker stems and will jeopardize achieving the overall height\u00a0you were targeting for a saleable plant. There are many PGR products\u00a0available and my only advice at this time is to read the label properly,\u00a0including proper application methods and any precautionary notes on\u00a0phytotoxicity and environmental conditions that can reduce product\u00a0performance.<\/p>\n\n
Two Pinching Techniques<\/h3>\n
Prevent after Pinch Stress<\/h3>\n
Temperature<\/h3>\n
Growth Regulators<\/h3>\n