Five minutes to moonflower

By: | Published: February 8, 2015 12:08 AM

The idea of a garden that blooms like clockwork has been around for centuries. But how well does it work?

The professionals said it could not be done. They had never tried it, and they didn’t know any public garden that had tried it, and they wouldn’t recommend anyone else give it a try.

This was not the response I expected when I called a few plant people and asked how to design a type of flower bed that has been around since the mid-18th century. It’s called a Horologium Florae: a flower clock.

“Please don’t show this to my bosses,” said Marc Hachadourian, the director of the Nolen Greenhouses, a 43,000-sq-ft grow facility at the New York Botanical Garden in the Bronx. What 41-year-old Hachadourian meant was, ‘don’t give management any ideas’.

He was joking. Mostly. Because once you hear it, the idea behind the flower clock is irresistible. First, identify a selection of a few dozen flowers that open and close at regular hours. They can be old friends like lilies, marigolds and primroses. Next, plant them in an organised fashion—perhaps in the segmented shape of a dial or clock face.

Here’s how the timepiece works. During a stroll in the summer garden, you notice that the sow thistle petals are open, while the adjacent pumpkin blossoms remain shut. The first plant, as per your records, blooms reliably at 5 am, the second at 6 am. Who needs a watch when the flowers know the time?

Like so many botanical concepts, the flower clock originated with the Swedish ur-taxonomist Carl Linnaeus in his 1751 treatise Philosophia Botanica. Based on field observations, he divided flowers into three categories. The meteorici open and close with the weather. The tropici follow the changing hours of daylight. And the aequinoctales, Linnaeus wrote, “open precisely at a certain hour of the day and generally shut up every day at a determinate hour”. From this third category, the aequinoctales, Linnaeus compiled a list of a few dozen plants to open and close with the hours: hawkweed, garden lettuce, marigold, day lily. Horticulture meets horology.

It seems unlikely that he ever planted one himself, says Gina Douglas, honorary archivist at the Linnean Society of London. It would be better, Douglas says, to think of the flower clock as a method for using the flora in the local landscape to estimate the time.

Over the years, the Linnean Society has received regular inquiries about the flower clock and how to make one. For the most part, Douglas says, nothing seemed to come of it. In 2008, a public art group in Vancouver, British Columbia, started a wiki to collect flowering observations. But to date, the Vancouver Flower Clock Project hasn’t produced a bumper crop of data.

Or maybe the problem with the flower clock is that it doesn’t work. Linnaeus, for a start, made many of his observations in the endless summer daylight of Uppsala, at about 60 degrees north. At more reasonable latitudes, these same flowers typically unfold later in the day.

Some of Linnaeus’s choices can be seen growing at the Brooklyn Botanic Garden, says 39-year-old Melanie Sifton, the garden’s vice-president for horticulture. But they’re not prize specimens in the collection; they’re roadside weeds and volunteers. European bindweed, for example, may open like the chiming of a clock at 5 am. But, Sifton says: “No gardener wants that weed. It has roots that go down to hell.” An even greater barrier to creating a floral clock is conceptual: the aequinoctales, those fixed-hour blooms, do not exist. Or not precisely as Linnaeus described them, anyway. We are wandering here from the Nordic wildflower meadow to the university laboratory and the study of photoperiodism. This is the relationship between day length and plant behaviour.

More than a century of research suggests that a flower’s circadian clock is filled with complications. Light is a dominant factor in opening and closing. These cues include the changing length of dark and light periods, the intensity of light, even the wavelength.

Temperature is another influence, and to a lesser extent so is humidity. Electric fields may play a role in flowering. Apparently a blossom carries a negative charge, while an insect in flight holds a positive charge. It’s hard to put one over on a dandelion.

All that said, some plants do show endogenous rhythms, or an internal clock. Selenicereus grandiflorus, a night-blooming cactus, will continue to open at the same hour, even after you’ve brought it inside and exposed it to darkness during the daytime and light at night. A field marigold moved from the garden to a dark room will still open its flowers on a 24-hour cycle.

A plant seems to practice a form of federalism: the flower obeys its own governor. A light shined on just the leaves apparently will not change the rhythm of the flower buds.

These mystifying habits have something to do with pollination. The white petals on a night-blooming cactus, Sifton says, attract not the morning bee, but a night flyer, the sphinx moth. At daybreak, the flowers shut to protect pollen and husband resources. Tracing the flower’s genetic pathways will get you only so far.

The poetry of the flower clock continues to grip the imagination. A few weeks ago, I’d stumbled upon a reference in the brand new novel Glow by the literary prestidigitator Ned Beauman. The plot involves pirate radio, a paid dog-walker with a non-conforming sleep cycle, Burmese mining concessions and a poppy-like psychoactive plant called ‘glo’, which blooms under 24-hour lights. You can probably guess how it all turns out.

When I reached him by Skype in London, 29-year-old Beauman confessed to a florid ignorance of practical gardening. “Actually, what I like about it is it’s so impractical,” he said of Linnaeus’ invention. “One imagines someone waking up in the middle of the night, putting on their dressing gown and then bending over in the garden and smelling the nipplewort and then saying, ‘Wow, it’s late’. And then going back inside.”

A few years ago, 32-year-old science writer Joshua Foer assembled a collection of seeds and sold out some 200 kits through Quarterly, a purveyor of curated packages.

Foer discovered the Horologium Florae while compiling an article for a magazine. He cited, for example, a ‘German woodsman’s’ plan for an ‘ornithological clock’, following the hourly birdsong of the green chaffinch (1 to 2 am), the black cap (2 to 3.30 am), the hedge sparrow (2.30 to 3 am), etc.

Seed packets seemed easier to ship than songbirds. “I myself can’t speak to whether this will work or not,” Foer said over the phone. “I don’t have a memory of anybody writing to me and saying they actually made this successfully.”

I finally found the working innersprings for an American flower clock in a place where I often go for personal guidance: the ‘Transactions of the Annual Meetings of the Kansas Academy of Science’. There, in 1890, a botanist named BB Smyth published a plant list based on prairie-flower studies.

Was it reliable chronometry or more doggerel? Smyth’s obituary recounts that after a single year of college, he became an authority on mathematics, geology and botany. This makes him either a polymath or a prairie charlatan in the mould of the travelling professor from The Wizard of Oz.

Sifton, from the Brooklyn Botanic Garden, liked the American tilt of the professor’s list. “He’s got a lot of cacti here,” she says, which she also grows in Brooklyn.

Then I brought in a ringer: Claudia West, a landscape designer and ecologist for the perennial plant company North Creek Nurseries. West, 31 years old, had the advantage of growing up on a family nursery in Germany, where Linnaean flower clocks (Blumenuhrs) are something of a cultural tradition, and occasionally pop up in parks.

Hachadourian says: “The way a gardener looks at time is very different. You look at growing seasons: spring and fall. How long it takes a vegetable to reach maturity. Whether you have two more hours after dark to finish weeding. I don’t think of horticulturists as clock-watchers.”

Put another way, who stands outside for hours, gazing at a starflower instead of a Samsung Galaxy? When you’re stalking a hawkweed at daybreak, time is an afterthought.

By Michael Tortorello

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