Where Are Poinsettias in Their Journey?
“Neil, I’ve been growing my poinsettia all summer, and I’d like to get it to bloom for Christmas. What do I need to do now?”
This is a quick and simple question to answer.
Poinsettias measure the length of the dark period each night (just like the mums in another story here this week). The hormone that triggers the change from vegetative to reproductive growth in their growing tips is destroyed by light.
That means that poinsettia plants must have total darkness for 14 consecutive hours each day. And, because they are growing vigorously right now, they must have full and bright sunlight during the daytime.
This “dark treatment” needs to begin immediately in order for them to be in full color between Thanksgiving and Christmas. They are very sensitive. Even a minute’s illumination from a room light, if it shines in the middle of the dark period, will delay blooming by one extra day.
Of course, poinsettias won’t tolerate freezing weather or anything below the mid-50s on a sustained daytime basis. If you want them to keep growing rapidly, you must protect them when it starts to turn colder.