Not easy. They need to be kept in total darkness for a certain length of time. Not sure how long, but it is hours a day rather than minutes and any bit of light will spoil the effect.

Looked it up for you and this is what it said:

Help your poinsettia to turn red by placing it in total darkness for 14 hours each day, starting eight weeks before you want to display it.
During the day, the plant needs bright light, but it should be placed in complete darkness every evening.

Have fun with that then!

Keep in mind that even a flash of light during the dark period may mean starting the process all over again.

I have done it about 5 times and it was a real faff. I did it as part of a botany project with the A- level students, that showed the effect of different wavelengths of light. They need 14 hrs of total darkness and as tug said even the shortest of breaks [opening the door and closing it quickly] in the dark stops it happening.

we also played around with wavelengths far red and far far red light. yes I know it is confusing but it helped the students get the idea that light has several different components and some were useful and others less so.

it is the wavelengths of light as well as hours of light that influences when plants form buds and then flower. it also explains why some spring plants have a second flush in the autumn.

Chrysanthemums, Christmas Cactus, and Easter Cactus won't try to form flower buds until the days are short and the nights are long, also. On the other hand, most onions won't try to form bulbs until the days are much longer than the nights. In the southern U.S., we have to grow special "short day" or "intermediate day" varieties to be able to make our pico de gallo or jambalaya, since our days don't get long enough to trigger the long day kinds.

that's interesting Tug. My students found it really confusing at times. The exam questions used to give light regimes that the students then had to interpret. intermediate varieties added an extra twist to it. ha!

then there was the added 'joy' of effect of light on germination. but that was another whole topic.

That's amazing. So would a flash of lightning prevent the bracts turning red too?

Hmm...I don't know, Yorkslass! Probably not with the wild species in its native Mexico, though winter is the dry season, there. Who knows what quirks the cultivated varieties have picked up in decades of being bred in greenhouses. In the U.S., the grower's greenhouses all have aluminized shades that are drawn over for 14-16 hours a day starting in September.

My Poinsettya turned red after I put it in a dark cupboard & then forgot all about it for 4 days :-). The bracts were small but it still looked quite pretty. I think buying a new one each year is the best idea.

It's a long arduous process Klahanie.

Go for it! Think how pleased you will be when it works! And let us know

I would love to see you pull it off Klahanie. Those velvety red leaves are magnificent. I don't think I have the patience. I would forget about it in the closet. Thank goodness for Walmart lol.

My poinsettia is outside. It is in the ground, and about 3 meters tall. It is in a place where it gets sun during the summer, but a lot of shade in the fall and winter. It turns red all by its self - it has the red bracts now. Later, the leaves will fall and it will grow again in the spring. Now that this has turned, it is time for the Strelitzia to start flowering. I would say that mine came from someone who had bought a commercially grown one, and then planted it afterwards, as I can't see how a plant from the original species in Mexico would get here.