Tick, Tock, a Flower Clock

Want to mark the hours by the blooms in your garden? It’s time to plant a flower clock.


| Fall 2016



Flower clock

From 2 a.m. to 9 a.m., see here which flowers will bloom around the clock!

Photos by Fotolia, iStock (4), and www.RareSeeds.com

Have you ever noticed that flowers seem to be on a schedule? Some wake up and show their faces to the sun the first thing in the morning, while others wait until later in the day or even dusk. Carolus Linnaeus (1707–1778) noticed. The father of modern plant classification even devised a floral clock based on the time at which the component plants open. (Check out “What’s in a Name?” to learn how Linnaeus designed botanical nomenclature.) You might want to try this fascinating idea in your herb garden. After all, flowers are a lot more fun to watch than a clock.

Timing’s the Thing for Your Flower Clock

What determines the time of day a flower opens?

Light seems to trigger the opening of poppies early in the morning on a sunny day. On a plant-collecting expedition to southernmost Sweden in June 1749, Linnaeus observed that scarlet pimpernel (Anagallis arvensis) opened at 8 a.m. and closed at midday. This little wildflower is also known as poor-man’s-weatherglass because flowers close or don’t even open in cloudy weather. Flowers of California poppy (Eschscholzia californica) also may not open at all on overcast days.

To maximize cross-pollination, many kinds of plants have evolved so that their flowers are open while their pollinators are most active. Meanwhile, pollinators have evolved so that they’re busiest when pollen or nectar is most available.

Nectar in chicory, for example, is produced only between 7 a.m. and noon on sunny days, the hours when its bee pollinators are most likely to stop in. The pollen of mullein, red poppies, and bindweeds (three of Linnaeus’ clock plants) is released only during the hours when bees visit them. Bee visits to wild mustard and some dandelions have been shown to peak about 9 a.m.; to blue cornflowers, 11 a.m.; to red clover, fireweed, and marjoram, about 1 p.m.; and to viper’s bugloss, about 3 p.m. — an indication of these flowers’ peak availability of pollen or nectar.

Dandelions, daisies, and some cacti appear to have a built-in clock that makes them open at daybreak and close late in the afternoon. These plants open and close on schedule, even when they’re kept in total darkness or constant light.





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