For poinsettias, the time of natural floral initiation\u00a0is centered on the period between\u00a0September 18th and 27th.\u00a0As long as the day length is not altered\u00a0artificially, cultivars will flower in 7 to 10\u00a0weeks after initiation, depending on the\u00a0response group of the particular cultivar.\u00a0Floral initiation is triggered by a critical\u00a0photoperiod of 12 to 12.5 hours, combined\u00a0with night temperatures below 70\u00b0F.<\/strong>\u00a0The actual date when this occurs can\u00a0be affected by environmental conditions.\u00a0Cloudy days and cool nights will result in\u00a0earlier floral initiation while bright warm days\u00a0can result in delayed floral initiation.<\/p>\n At the time of floral initiation, night temperatures should\u00a0be reduced to between 68 and 70\u00b0F. Night temperatures\u00a0above 73\u00b0F can delay flowering. After floral initiation, flower development\u00a0is a continuous process culminating with anthesis, that is, the\u00a0shedding of the first visible pollen from the flowers (cyathia).\u00a0The progressive stages of flower development can be identified by\u00a0several visible indicators. The stage when first flower bud (cyathium)\u00a0is visible to the eye is termed simply visible bud. First colour refers\u00a0to the stage when the green bracts show the first colour change as they transition toward their final colour.<\/strong> Generally speaking, with night\u00a0temperatures at 70\u00b0F, floral initiation occurs at 14 to 18 days after the\u00a0start of short days (SD), first colour at 30 to 32 days after SD, visible\u00a0bud at 35 to 39 days after SD, and anthesis at 54 to 59 days after SD.<\/p>\n The average daily temperature after the appearance of bract colour\u00a0is critical to bract development. Daily temperatures of 68 to 70\u00b0F are\u00a0needed during this period to maximize bract size. If possible, try to\u00a0avoid temperatures above 75\u00b0F, which can result in very large but soft\u00a0bracts that are more susceptible to post-harvest problems.<\/p>\n As days become shorter and light quality diminishes, it is very\u00a0easy to overwater plants at a time when their transpiration rate\u00a0is reduced. Stay on top of weather forecasts and make an\u00a0attempt to water according to the weather. In particular, try\u00a0to avoid heavy watering just prior to extended dull, cold\u00a0periods.<\/strong> Shortly after flower initiation, a poinsettia\u2019s demand for fertilizer\u00a0is reduced as the plant transitions from vegetative\u00a0growth to flower and bract development. Monitor salt levels\u00a0closely and avoid allowing them to climb too high prior to\u00a0this transition.\u00a0After the pinch, 30% of the total nitrogen should be in the\u00a0ammonium form to facilitate optimal leaf expansion. By the end\u00a0of September, the plants should have reached their desired growth\u00a0and leaf expansion; at this point, ammonium-N should be reduced\u00a0to 15% of the total nitrogen, a level that supports mid- to late-season\u00a0growth while avoiding post-harvest quality issues.<\/strong><\/p>\n Even though the rapid growth phase after pinch is complete, there\u00a0is still a potential for stretching during weeks 40 to 44. To keep the\u00a0plants within the desired range for final height, try to establish a method\u00a0of monitoring growth prior to this period of optimal bract expansion.\u00a0Avoiding applications of plant growth regulators (PGR) during this final\u00a0stage of bract development is often recommended, so as not to reduce\u00a0bract size. However, if tall plants warrant an application of PGRs during\u00a0this period, use of modified methods or application of specific PGRs\u00a0should be considered.<\/p>\n Understanding latent infections is\u00a0essential to addressing common\u00a0diseases of poinsettia such as\u00a0botrytis<\/em> and powdery mildew.\u00a0A latent infection is one that is\u00a0hidden, inactive or dormant\u00a0until the right conditions\u00a0exist. Latent fungal infections\u00a0of plants occur with\u00a0no visible symptoms until\u00a0the spores germinate\u00a0under the right conditions.\u00a0In the case of botrytis,<\/em> the\u00a0fungal spores (conidia)\u00a0serve as the initial inoculum.\u00a0After landing on the\u00a0surfaces of the plant, the\u00a0conidia can remain dormant\u00a0for at least three weeks before\u00a0germinating.\u00a0In the fall, these fungal diseases can\u00a0move into the crop unnoticed, a situation\u00a0that warrants manipulation of heating\u00a0and ventilation to dry the greenhouse atmosphere\u00a0at the end of the day.<\/strong><\/p>\nTemperature<\/h3>\n
\nWatering<\/h3>\n
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\n![\"poinsettia\"](\"https:\/\/www.berger.ca\/en\/wp-content\/uploads\/sites\/2\/2016\/07\/flores-nochebuena-300x200.jpg\" "\\"Poinsettia")
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\n<\/div>\nFertilization<\/h3>\n
Growth Regulators<\/h3>\n
Diseases<\/h3>\n