Start by keeping your Poinsettia healthy and happy during the indoor holiday season. Make sure your plant gets plenty of good light. Poinsettias can take full sunlight though they will survive with less. Make sure yours is potted in a fast-draining medium and keep it slightly on the dry side: make sure the surface of the soil dries out before watering it again. It's a good idea to keep a pan or tray beneath the pot to avoid water staining the floor below when the water drains through the bottom of the pot. It's an even better idea to fill the tray with pebbles so the pot doesn't sit in drained water which can suffocate the plant's roots.
Poinsettias can be toxic if eaten in very large quantities and their sap can be a skin irritant to some people. But these plants are not as highly poisonous as once thought. Still, it's best to keep the curious mouths of children and pets from nibbling on them.
Buy a poinsettia that has not yet opened its flowers. The big colorful bracts that look like flowers are not flowers at all, but specially adapted leaves. The flowers are at the center of the bracts and are little yellow and green clusters that often look moist or sticky. If the flowers in the center of the colorful bracts are still in bud when you buy it, the plant is likely to stay showy longer. Once the plant has finished blooming, the leaves will start to wither from the bottom up eventually leaving just a few colorful bracts. At this point you can plant your indoor Poinsettia outdoors in the garden if you live where temperatures are not likely to fall much below 40'F. If you move it from indoors to outdoors in bright sun, give the plant some temporary shade protection to let it slowly adapt to the brighter light. Know that Poinsettias can easily grow to six feet in height if happy planted in the ground.
If you want to grow your Poinsettia on in a pot after it has finished its holiday bloom, give it a rest for the rest of the winter months by watering less. Continue to give it good light. You can also cut the plant back to shorter stems. Once the Poinsettia sprouts back into active growth in the spring, give it as much light as you can, a mild feeding and start watering it regularly. Do not over-water. You also may want to pot it up to the next size container -- especially if your pot is filled with roots --using a fast-draining soil mix.
Come late summer or early autumn you will want to make the plant think the days are shorter than they really are to initiate flowering early â in time for the holidays. Naturally, these plants will bloom in spring and summer. It is the longer hours of dark that encourages them to set their colorful bracts and bloom. So at the end of August or the beginning of September you will want to make them think it is late winter by giving them long nights with no light. The easiest way to do this is to put the plant into a dark closet so it gets a around 14 hours of dark each evening. Bracts should start coloring up nicely by November so your Poinsettia should look perfect for the holidays.