you are aware ... consistent with the name.. they open at 4 oclock ... and maybe only for that one day ....

give them another week ... should be quite a show ... VERY fragrant en masse ... in the evenings ...

soil looks very dry .... perhaps more water ... dont think the cosmo has anything to do with it.. unless not enough water ...

some random leaf damage on other things.. how close are you to drought conditions????

ken

Ok, folks -- I wasn't aware that simply posting a question on GardenWeb can solve a problem by itself. But that's apparently what has happened here. I swear I've been outside viewing that plant in late afternoon and early evening and have not seen flowers on it. I'm sure of it! Well, uh, um, at least I thought so...

In any case, that first photo with no flowers was taken at 6:20 pm. I then posted my note here, and Ken kindly answered. At 7:35 pm I was back outside, and saw to my amazement....

The power of GardenWeb!

Rick, they don't open at four but in the late afternoon through the evening hours.

Have people found that their Four O'Clocks bloom around the same time each day? I'm doing some time-lapse photography right now to see if I can catch it. Yesterday they bloomed somewhere between 6:20 and 7:35. Right now it's 7:20 and I'm not seeing anything yet. I'm curious to see if the time of blooming is fairly steady over a period of a week, or random, or if the bloom time gets earlier, or later, as the season goes on, or if it's dependent on some not-fully-studied environmental factors, or...

[Half hour later: Oh, well, a watched pot never boils. Since it knows I'm recording it, it's refusing to open, or it'll open much later than the time it did yesterday when I wasn't paying attention. Now that it's getting dark and it knows I can't record it, it'll now decide to open...]

They are stimulated to bloom as the sun begins to fade. This effect will be diminished in partial shade, on cloudy days, etc.

dont forget ... in your experiments.... that plants dont put up with daylight savings time.. and all that nonsense ...

and that is basically what rhiz said ... its the declination of the afternoon sun that triggers it ...

also.. i believe this plant is also known as the marvel of peru ... where its native.. so you could probably add elevation as a variable ... if you were going to go all science on an experiment ...

ken

In the future, if an option, try putting 4'o's on the east side of the house (or other larger plant) so they fall into shadow sooner, as long as it's a spot with 6+ hours of direct sun earlier in the day. That would get the blooms opening as soon as possible in the evening.

Conversely, planting morning glories on the west side can help to have blooms that stay open for an hour or 2 longer in the morning.

Thank you for all the suggestions, all. My 4'o's didn't bloom last night at all except for one flower opening up part-way. Maybe some days there are no blooms?

I'm curious to know: do your plants bloom *approximately* the same time each day, factoring in the fact that solar declination is taking place a bit earlier every day as August progresses? In other words, do you sometimes get flowering at 4:30 and then the next day 7:30, or....?

Heat, humidity, clouds or lack of, probably all at play. You can't set your watch by these blooms at all. If the spot they are in currently is in the direct sun until sundown, the blooms will open later than a plant onto which a shadow has fallen well before sunset.

Ah, if only I knew at the beginning of the season what I know now.... :-)))