the holly and the ivy or plant hacks

The poinsettia (Weihnachts-stern) will only naturally produce these brilliant, festive red leaves under very narrow conditions, when exposed to equal periods of light and darkness over successive days, which only occurs in the tropics at wintertime. Of course florists and growers know these sorts of floral hacks to achieve the same result—as do brewers and bakers and apothecaries, but I do not know if there are any other strictly decorative and devotional tricks for the plant kingdom. Wreaths of holly, Christmas trees and garlands are certainly transformations but not at their own accord, but perhaps the myth and magnetism of mistletoe is something in the same category.