How to care for a poinsettia in bloom
Place your poinsettia in a well-lit room, with as much indirect sunlight as possible.
Keep the poinsettia at normal room temperature, but not above 20°C. Nighttime temperatures of 16 to 17°C are best. Too much heat will shorten the blooming period. Poinsettias are sensitive to extreme temperatures (below 10°C and over 30°C). Avoid placing your plant too close to any heat source or on top of a television. Keep it away from cold drafts, as well, and protect it between the store and your home.
Water in moderation with tepid water when the soil is dry to the touch. Thoroughly soak the soil mixture, but avoid overwatering, as this can cause root rot. Never leave any water standing in the saucer. Allow the surface of the soil to dry out between waterings.
There is no need to fertilize your poinsettia while it is in bloom.
After blooming, the vegetative growth period begins
Depending on the cultivar, a poinsettia may remain in bloom for four months or even longer. After that time, its bracts will gradually lose their colour. Most people buy a new poinsettia every year. If you want to keep yours as a green plant, or if you are a very enthusiastic gardener and want to try coaxing it to rebloom, follow these tips:
Pruning and repotting
In late April, prune your poinsettia, cutting all the stems back by one third. For a more compact plant, keep only two or three leaves on each stem. Be sure to mist the plant with water to limit the seepage of latex and prevent it from drying out.
Poinsettias do not like to have " wet feet ". Repot the plant in an aerated, well-drained medium. You can use a ready-mixed commercial substrate or blend your own, using equal parts potting soil, perlite and peat moss.
Prune the plant again in late July or early August, or pinch back the ends of the stems (leaving three or four leaves per stem) to encourage bushy, compact growth. Never pinch a plant back after early September if you want it to rebloom.
Once all risk of frost is past (and ideally once temperatures remain above 13¡C), take the plant outside for the summer. Do this gradually. Place it in a semi-shaded or even sunny spot. If you cannot take your plant outside, give it as much light as possible, even full sun.
After pruning, a temperature of 20°C is ideal. During the growing period after that, indoor temperatures of 20-24°C are adequate.
After pruning, the poinsettia will require less water. Give it only enough to prevent the soil from drying out completely. Once growth resumes, water as necessary, allowing the soil surface to dry out between waterings. Outside, especially in full sun, be sure not to let it wilt!
After your poinsettia has finished blooming (from late April to mid-September), apply a soluble fertilizer, such as one labelled 20-20-20,* once a month. Once new leaves appear, increase the frequency of fertilizing (every two weeks) to promote vigorous growth.
*NB: Fertilizer with a smaller amount of phosphorus and an N-P-K ratio of 3-1-4 or 2-1-2 is ideal (labelled 17-5-19 or 20-10-20). This type of fertilizer is hard to find, however, so you can also use an all-purpose soluble fertilizer such as 20-20-20. Always follow the directions on the label.