A Garden of Blooms You Can Set Your Clock By

By Joel M. Lerner
Saturday, February 9, 2008

Most floral clocks are simply outdoor motorized timepieces with ornamental flowers in the shape of a clock. But what if you could coordinate the blooming so that the flowers would open and close at set times of the day? Now that would be an innovative way to tell time.

Although it's labor-intensive, creating a floral clock can be an interesting project. You still have time to plan one this winter and plant it in spring.

A floral clock is driven by the plants' own biological clocks, which tell the plants when to open their leaves and flowers. The reason flowers open at certain times depends on complex cell biology, evolution, light, temperature and atmospheric conditions, all of which are genetically coded. Plants developed these biological responses over tens of thousands of years. Those that didn't adapt to proper opening or closing times didn't survive.

Swedish botanist Carolus Linnaeus first made the connection between flowers and time. In 1750, Linnaeus researched and planted a Horologium Florae, or "sundial of plants," based on his observations of plants that bloomed at fixed times, regardless of weather conditions. He arranged the plants in the pattern of a clock by the hours that their flowers opened or closed.

Day-blooming flora depend on day pollinators, such as bees, birds and butterflies, to procreate. Moths or bats often pollinate plants with night-blooming flowers. Some wind-pollinated plants, such as grass, can delay opening when it's too wet for their pollen to be carried by the wind. Other flowers open only when humidity is low. These blueprints are set by the plants, yet, regardless of the reasons that they open and close, they seem to follow the same circadian rhythm, a 24-hour day, by which we live.

Linnaeus studied the opening and closing times to design his floral clock. For example, the daylily closes between 7 and 8 p.m. Cat's ear and catmint ( Nepeta) open at 6 a.m. and close between 4 and 5 p.m. Passionflower ( Passiflora) opens at about noon. If you study the habits of enough plants, you can create your own floral clock to act as a natural timepiece in your garden.

The plants listed with this column are not the only plants that have specific opening and closing times.

For example, there are about 25 species of night-blooming cereus and 125 species of evening primrose. Other plants also come in a variety of species and hybrids. Some will be dependable and enjoyable plants to watch; others won't work as well, and you will have to replace them. As I've often emphasized, such experimentation is an ongoing part of garden design.

Much of this list of flowers is based on plants that Linnaeus recommended. I updated some botanical names and added a few plants he might not have used. Most of the blooming times are accurate to Uppsala, Sweden, where Linnaeus grew these plants. It's at roughly the same latitude as Juneau, Alaska. You will have to determine the precise hour of opening and closing of these "clock flowers" in your region.

As you scrutinize the habits of plants' petals, you'll learn other facts about them. For example, morning glories begin to close around noon, implying they do not like afternoon heat. Scarlet pimpernel is open most of the day but closes at the approach of bad weather. Daylilies are open for only one day, from morning until they close by sunset. Many of these plants are annuals or perennials and can be grown from seed in the spring or summer. Start planning, ordering seed, growing and timing some flowers now.

Check with your garden center first to see whether you can get plants there. If not, here are some mail-order seed sources: Renee's Garden ( http://www.reneesgarden.com), Thompson & Morgan ( http://www.tmseeds.com), Burpee ( http://www.burpee.com), Heronswood ( http://www.heronswood.com), Brent and Becky's Bulbs ( http://www.brentandbeckysbulbs.com), Park Seed ( http://www.parkseed.com) and Seeds of Change ( http://www.seedsofchange.com).

The more you learn about your Horologium Florae, the more you can add to it. I would love to hear from those of you who can tell time from your gardens.


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