Bonsai - Poinsettia:

You can make a poinsettia change colour again the next year. They need fourteen hours of absolute darkness and ten hours of bright light for three months in order to change colour, and if you make a mistake and give it even one long day (or short night) it is back to square one! In addition, plants purchased at Christmas time are treated with growth retardant hormones to become short and bushy. These wear off after a year, so the next year the plants are long and leggy, trying to turn into trees. However, difficult you may find growing poinsettia bonsai the reward is often worth the effort.