How do plants know it’s Christmas – wien.ORF.at

This phenomenon is called the photocycle. If, from September onwards, daylight hours become shorter than twelve hours (i.e. days become shorter), this stimulates flowering in some plants. Research has shown that it is enough to try individual parts of the leaf on this shorter day. Special proteins (called flowering T locus proteins) then send messengers to the entire plant, which then begins to form flowers. In addition to poinsettias and Christmas cactus, typical short-day plants include coffee, cotton, and sugarcane.

Many of our vegetable and bedding plants can be found among the long day plants. Spinach, lettuce, beans and almost all grains should bloom and set seed in the summer before the cold sets in so they have seed for next year. In addition to these two large groups of light-controlled plants, there are also day-neutral plants – the most famous of which are tomatoes, cyclamen, and – although they seem unusual – sunflowers.

In addition to controlling light, plants also react to periods of drought. This is important, for example, in the Christmas cactus, an epiphyte from the coast of Brazil. It should be watered little or not at all from mid-August onwards. The tips of young green leaves can wilt. Once the little flower buds appear in November, start watering carefully again and soon after that the plant is in full bloom.

Many Christmas cacti — botanically called Schlumbergeras, named after a French cactus researcher — are now cultivars created through horticultural breeding. Many large flowers in a wide range of colors are found in endless crosses, similar to poinsettias, which today have little in common with their Mexican origins. There it becomes a huge shrub two or three meters high, and here it now grows very compactly and no longer needs chemical treatment to keep it small. What sticks with these two Christmas plants is their love of thriving on the short days in the Northern Hemisphere. Exactly at Christmas time.

You can read all the tips from Vienna Radio’s plant expert, Karl Ploberger, here.