Each year when we buy our new poinsettia in December we think about how we can make it re-bloom for the next year.
To have a poinsettia plant that is full and attractive, you needed to cut the poinsettia back to about 3 to 4 inches in mid to late April. This will get rid of all the old growth and give a base for new growth to start. It will also keep the poinsettia from getting too large.
Then after the new growth has established, you pinch back the poinsettia plant in early July. This will cause each of the new stems to branch out creating a fuller bush.
Now starting in late September, you need to give the poinsettia plant 12 to 14 hours of continuous darkness each day for 8 to 10 weeks to get the poinsettia to produce the colorful brachts in time for a December display.
You can do this by many methods, but it is important that the process is not broken. It must be done each day for the period. The darkness must be total. Room lighting for regular living will be enough to affect the process. Even the light from a street light outside can affect the production of the colorful brachts.
Some people will place the poinsettia in a darkened room at night. The curtains should be drawn and the room should not be visited during the 12 to 14 hour period. Even the turning on of the room light for a short period will affect the poinsettia.
Instead of using a room, you may use a closet for the dark period. Again the closet should be kept completely dark and the light should be blocked from getting in through the cracks around the door.
Another way is to enclose the poinsettia in a dark garbage bag for the 12 to 14 hours of darkness. The bag must be very dark and thick so as not to let in the light through the bag. Manufacturers of garbage bags are getting very good at making strong bags with thin sides and coloring them green. This allows too much light to pass through, so choose a heavy black bag. When using this method you also want to support the bag so that it does not touch the poinsettia leaves. Also during the daylight hours, lower the bag completely so that the poinsettia can breathe.
During this 8 to 10 weeks, the poinsettia needs to be returned to the bright light during the daytime. The poinsettia plant is still growing, producing the brachts or colorful leaves that we want.
Re-blooming last years poinsettia requires some patience, but you can produce a beautiful houseplant to add to your winter decorations.