A village is famous for its flowers and wants to bring in tourism by replacing its timekeeping and basing everything around a flower clock. Schools and shops all agree to set their times by the flower clock and a webcam image of it is streamed across the village for everyone to see what time it is.


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How do they make the flower clock both accurate enough for regular use and usable in all seasons? They are in a mild temperate climate so there is some seasonal variation in temperature but rarely frost. Ideally this should be as natural as possible but some technological assistance is allowed.

  • $\begingroup$ It's possible if you divide this flower clock into different greenhouses, each one is engineered to sustain a type of flower in order to provide light, heat, humidity and other climates, so the clock will function properly. $\endgroup$
    – Javert
    Commented Mar 8, 2016 at 10:24
  • $\begingroup$ @Javert A single greenhouse would be fine. Multiple greenhouses wouldn't really give a clock effect although I guess you could have a single glass wall between each section of the clock and keep the desired look. $\endgroup$
    – Tim B
    Commented Mar 8, 2016 at 12:06
  • $\begingroup$ The problem isn't so much the multiple greenhouses as the fact each one would have to be lit and heated or shaded and cooled at the right times to trigger the flowers. $\endgroup$
    – Separatrix
    Commented Mar 8, 2016 at 12:29
  • $\begingroup$ This is a really cool idea. Do you have any sense as to what sort of jitter and drift is acceptable for these clocks? Making a clock that tells you roughly what hour it is will be much harder than a clock that can measure things down to the minute, or bloom at the same time of day two days in a row with minute precision. $\endgroup$
    – Cort Ammon
    Commented Mar 8, 2016 at 22:49
  • $\begingroup$ I was wondering why a villain wanted to bring in tourism using flower clocks, then I re-read the first few words. $\endgroup$ Commented Mar 8, 2016 at 23:49

4 Answers 4


In practice it can't be done, but that's no fun. Flowers are highly seasonal and the ones that open or close at different times of day are fairly approximate time keepers. Flower clocks, while they do exist, rarely go beyond having a circular flower bed with a clock mechanism
or sundial built in. Such as this one at the botanical gardens (Łódź) Floral Sundial


2 a.m.: Common Morning Glory (opens) Night-Blooming Cereus (closes)
3 a.m. Imperial Morning Glory (opens 3-4 a.m.)
4 a.m. Yellow Hawkweed (opens) Dogrose, Chicory, Yellow Goats-Beard (opens 4-5 a.m.)
5 a.m. Buttercups, Poppy (opens) Dandelion, Morning Glories, Wild Roses (opens 5-6 a.m.)
6 a.m. Spotted Cat's Ear (opens) Flax, Potatoes (open 6-7 a.m.)
7 a.m. African Marigold, Lettuce, White Water Lily ( opens)
8 a.m. Mouse-Ear Hawkweed, Scarlet Pimpernel (opens) African Daisies, Nolana (open 8-9 a.m.) Dandelion (closes 8-9 a.m.)
9 a.m. Calendula (Field marigold), Catchfly (opens) Coltsfoot, Gentians, Sandworts (opens 9-10 am) Prickly Sow Thistle (closes)
10 a.m. Common Nipplewort (closes) Star-of-Bethlehem (opens 10-11 a.m.) California Poppies (open 10a.m.-1 p.m. only in sunlight)
11 a.m. Star-of-Bethlehem (opens)
Noon Goatsbeard, Blue Passion flower (opens) Morning Glories (closes)
1 p.m. Carnation (opens) Childing Pink (closes)
2 p.m. Afternoon Squill (opens) Scarlet Pimpernel, Water Lily (closes) Chicory, Dandelion, Poppy, Potatoes, Sandworts (closes 2-3 p.m.) Dandelion (closes 2-5 p.m.)
3 p.m. Hawkbit (closes) Calendula, Spider plant (closes 3-4 p.m.)
4 p.m. Purple Hawkweed (opens 4 p.m.) Four O' Clocks(opens 4-7 p.m.) Small bindweed, Allyssum (closes) California Poppies, Cat's Ear (closes 4-5 p.m.)
5 p.m. Night-Flowering Catchfly (opens 5-6 p.m.) Chicory, White Water Lily (closes) Coltsfoot (closes 5-6 p.m.)
6 p.m. Showy Evening primrose, Goatsbeard, Moonflowers (opens) White water lily (closes 6-7 p.m.)
7 p.m. White campion (opens) Fig-marigold (opens 7-8 p.m.) Iceland poppy (closes 7 p.m.) Daylily, Dogrose (closes 7-8 p.m.)
8 p.m. Night flowering cereus (opens 8-10 p.m.) Catchfly, Dandelions, Daylilies (closes 8-9 p.m.)
9 p.m. Flowering Tobacco (opens 9-10 p.m.)

I wouldn't set my clock by it, but it would make a good centrepiece for your village. It even includes a water feature. If your village is happy to move to a slightly casual version of local solar time, then it would work nicely. There's no real reason why not beyond its hopeless inaccuracy.
Someone has actually built one, note the small water feature as promised.
Linnaeus clock

'It's not very accurate in the small hours. There aren't too many night-blooming plants that grow well up here. They open for the moths, you know-'
'It's how time wants to be measured', said Lobsang

Thief of Time: Terry Pratchett

  • $\begingroup$ Nice. Now all we need is to know how to setup Daylight Saving Time! $\endgroup$
    – SJuan76
    Commented Mar 9, 2016 at 0:57
  • 1
    $\begingroup$ @SJuan76: You could start with the same approach the National Trust uses for Stone Circles $\endgroup$
    – Separatrix
    Commented Mar 9, 2016 at 8:53
  • $\begingroup$ +1 For the List. And the water feature. And the Pratchett quote. Good man. :) $\endgroup$
    – fgysin
    Commented Mar 9, 2016 at 12:41


Install a large sundial.

Plant a species of flowers that will open up in nice flowers only when in shade of that sundial.

Sure, it's cheating, but it will be accurate.

  • 1
    $\begingroup$ I don't consider that cheating :) It's the sort of creative answer I was looking for. $\endgroup$
    – Tim B
    Commented Mar 8, 2016 at 14:55

During daytime with sunny weather (so at the same circumstances a sundial works), sunflowers (hence their name, I guess) turn their "heads" (i.e. blossoms) toward the sun. Not as precise as a sundial, but you can gain precision by averaging over a large number of sunflowers and by computing a mapping from sunflower orientation to time-of-day. (They don't fully turn toward the sun.)

To make this usable without it looking more like a computer output than something flower-related, have one camera for each involved sunflower, filming the respective flower from above. On the web stream, superimpose the images of all those flower-cams, and overlay them with a dial that has the non-linearity of the flower-head-turning already computed in. (That is, the dial will be slightly irregular.)

  • $\begingroup$ This is likely the most accurate of the purely natural options $\endgroup$
    – Separatrix
    Commented Mar 9, 2016 at 16:58

To expand on user16295's answer: bees.

The answer remains 'impossible', but this might be a nice addition to your clock. Some papers suggest that bees learn the time of day a flower will open. You could reason that looking at the bees can give a better indication of the time, because the bees compensate for the fluctuations caused by temperature. Just don't forget to stick a beehive in the middle of your clock.


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