how to get last years poinsettia to flower

they need 14hrs total darkness.for at least 60days. put a black poly bag over it and if you forget one day to uncover it dont worry. if you forget to cover it then you are back to the begining.

I've started putting a plant I have in a dark cupboard at night.

I used to get one plant I had in Spain to flower every year for about 5 years by covering it with a black bag from when the children started school after their summer holidays till the "flowers" were colouring up nicely. Never did check on how long that took.

Just bear in mind that the flowers will be less than 1/2 the size when bought!
The plant will probably be twice the size as it was when bought!

I've never succeeded in keeping alive long enough to have to do but know that SBG's advice is correct.

A quick search on Google & I found this very informative page:

http://www.gardenguides.com/how-to/tipstechniques/containerindoor/houseplants/poinsettia.asp