The circadian rhythms of plants
As early as the 18th century, Swedish naturalist Carl von Linné determined that flowers have their very own biological rhythm, as they open and close their blooms at very different times. Whereas the poppy, for example, blossoms in the early morning, the evening primrose prefers to blossom in the evening. Why isn't nature set up in such a way that all flowers blossom as the first rays of sunshine appear? The answer is quite simple: This harmony of different flower blooming times has an important role to play in nature by providing insects with a round-the-clock supply of pollen and nectar. One of the benefits of this is that the insects know exactly which flowers are open at what time, removing the need for a long search for nourishment. Another benefit is that the competition for food is less intense for all the bees, bumblebees, butterflies and hoverflies. This clever rhythm also has advantages for flowers as they do not have to compete amongst one another to attract insects for pollination.
As a rule, different plants need specific insects for pollination because of the differing structures of their flowers. For example, the evening primrose reproduces with the help of moths, whose long proboscis allows them to penetrate deep into the flower. Moths start their rounds in the late evening when the garden has become a safer place for them, as the birds have settled down for the night. To be pollinated, the evening primrose has adapted its flowering time to the moth and only opens its delicious fragrant luminescent yellow flowers in the late evening. An added benefit of this is the energy saved by the evening primrose.
Flower clocks and weather forecasts
Based on this knowledge, in 1745, Carl von Linné planted the first flower clock in the Botanical Garden of Uppsala in Sweden. He created a round flower bed split into 12 segments. Each segment of the flower clock represented exactly one hour of the day and was filled with plants in such a way that flowers opened or closed at a moment corresponding precisely to the time of day. Supposedly, Carl von Linné used his flower clock to tell the exact time, give or take five minutes. Today, flower clocks are considered as more of a gimmick of natural history and a head-turning ornamental feature, but this does not mean they have lost their charm. Despite the modern world in which we live, where every Smartphone tells the time, the flowering times of individual flowers can still be useful. For example, when you are working in the garden, just a quick look at the open Jack-go-to-bed-at-noon flowers is enough to tell you that it is almost time for lunch.
Likewise, flowers can also tell you whether you need to water them or not that day. If the marigold has not yet opened its flowers at seven o'clock in the morning, then this signalises that the weather will be bad for the day. If it closes completely, a storm is probably on its way, so start picking up all the gardening implements lying about the garden!