Have you ever noticed how 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. 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
What determines the time of day a flower opens?
Light seems to trigger the opening of poppies early in the morning of 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’s 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; even when the plants are kept in total darkness or constant light, they open and close on schedule.
The flowers of four-o’clock (Mirabilis jalapa), evening primroses (Oenothera spp.), and a number of other plants open a certain fixed number of hours after dusk on the previous day. Since dusk occurs later and later on successive nights until the summer solstice and then increasingly earlier, it’s rare that four-o’clock flowers open exactly at 4 p.m.
In crocuses and tulips, a temperature increase of about 20°, such as occurs at daybreak, causes the upper side of the petals to grow faster than the underside for a time, which makes the flowers initially open wide. Later on in the day, the upper side stops growing while the underside continues to grow slowly, causing the flowers to become more cup-shaped.
The Herbal Clock
Many clock flowers have a history of herbal use. Here are a few, listed in order of the time of day that they open; these times vary according to latitude and season.
• 2 to 8 a.m. Morning glories (Ipomoea spp.) and bindweeds (Convolvulus spp., Calystegia sepium) include desirable garden flowers as well as noxious weeds. All have a vining habit and attractive, funnel-shaped flowers; many kinds were once used as purgatives.
• 4 to 5 a.m. Corn poppy’s (Papaver rhoeas) young leaves can be used as a potherb or to flavor soups and salads. Pigment from the petals was once used to color wine, and a syrup has been used in soups and gruels. The seeds may be used in baked goods or pressed for their oil, said to be a good substitute for olive oil.
• 5 to 6 a.m. Dandelion (Taraxacum spp.) leaves are used as spring greens, the flowers in dandelion wine, the roots as a coffee substitute. Although their flowers open and close like clockwork, many dandelions set seed without being pollinated at all.
• Nipplewort (Lapsana communis) is a European annual wildflower related to dandelion that was once used to treat sore nipples.
• Goat’s-beard, also called Jack-go-to-bed-at-noon (Tragopogon pratensis), and salsify (T. porrifolius), or vegetable oyster, have taproots that are eaten like parsnips. The young flower stalks may be cooked as you would asparagus. Goat’s-beard has a yellow flower; salsify, a pale purple one. Both “go to bed” at noon. The seed heads look like big dandelion blowballs. Both were once used to treat disorders of the liver and other organs.
• 7 a.m. Pot marigold (Calendula officinalis) is an annual herb whose fresh florets are sprinkled on salads or dried and used for seasoning or coloring various foods. Poulticed on cuts and burns, they reduce inflammation and promote the growth of healthy new tissue. Flowers of the related field marigold (C. arvensis) open about two hours later.
• Wall lettuce (Mycelis muralis) is a European perennial wildflower whose toothed leaves are sometimes used in salads.
• Water lilies (Nymphaea spp.) are astringent, soothing herbs with edible seeds and roots.
• 7 to 8 a.m. The fruits of West Indian gherkin (Cucumis anguri) are eaten raw, cooked, or pickled like those of garden cucumber (C. sativus).
• 8 to 9 a.m. Yellow gentian (Gentiana lutea) is the source of an extremely bitter substance used to stimulate the appetite and aid digestion.
• Spatterdock, or yellow pond lily (Nuphar lutea), has edible leaf stalks and roots. The roots are a source of starch. The seeds may be parched and eaten or ground into flour. The flowers yield a refreshing beverage.
• Scarlet pimpernel (Anagallis arvensis) closes by 3 p.m. or whenever clouds threaten. Once used to treat bites of rabid dogs, improve vision, cleanse the skin, prevent witchcraft, and dispel melancholy, as well as draw out splinters and promote perspiration, it is now considered too toxic for internal use.
• 9 a.m. Mullein (Verbascum spp.) flowers contain mucilage that is used to treat throat irritations and coughs. The leaves or flowers may be brewed into a beverage tea.
• 11 a.m. Star-of-Bethlehem, or lady eleven-o’clock (Ornithogalum umbellatum), has white star-shaped flowers that may be baked in bread.
• Noon. Ice plants (Mesembryanthemum spp.) are low-growing South African succulents whose acid, salty leaves may be eaten raw, cooked, or pickled, or used as a garnish. The name Mesembryanthemum comes from Greek words meaning “midday flower” (that being the time when many of its species open). Others, however, open in early or midmorning or in the evening.
• 1 p.m. Carnation (Dianthus caryophyllus) has edible flowers and was once used to treat fevers. The oil is used in the perfume industry.
• 2 p.m. Acanthus-leaved thistle (Carlina acanthifolia) is a stemless perennial thistle whose flower receptacles may be cooked like artichokes. The flowers are also used in dried arrangements. The genus is named for Charlemagne; one species is said to have cured his army of the plague. It has also been used as a purgative, to promote sweating, and as an antiseptic.
• 4 p.m. English or narrow-leaved plantain (Plantago lanceolata) bears spikes of minute flowers. Mucilage and antibacterial glycosides in the leaves soothe coughs and help heal wounds. Mucilage from the seeds was once used in France to stiffen fabric.
• 6 to 8 p.m. Some evening primroses (Oenothera spp.) open at dusk and are pollinated by night-flying moths; others open during the day. The roots, shoots, flowers, and seedpods of some species are edible. This is true of common evening primrose (O. biennis), whose oil has been recently promoted as a treatment for premenstrual syndrome and atopic eczema.
Planning a Flower Clock
Choose a spot in full sun. Many clock flowers open “on time” only if they have a sunny exposure.
The time at which different flowers open where you live may differ from the times listed above and may be expected to change further as the season progresses. For ease in fine-tuning your first clock, consider making a container clock. Plant several pots, each with a different clock flower. Place a single large plant or several small plants in each pot. Arrange them in a circle, arc, or line—or however you’d like to watch the progression of opening flowers. Note at what time each kind of flower opens. Rearrange the pots if necessary so that the flowers open in sequence.
If there’s an hour when none of your flowers is opening, look around the garden or the countryside to see if you can find a flower that opens at that time. Pot one up and add it to the clock. Ordinary garden soil or potting mix (for containers) and regular watering will suit most clock plants, but a few kinds will require special treatment. Water lilies and spatterdock, for example, should be grown in water in tubs. As the summer goes on, note any changes in the time each kind of flower blooms. After you’ve worked out the details, you may want to establish a special bed for your floral clock.
Betsy Strauch is an assistant editor at The Herb Companion. She has a good time with her flowers.