Gadenin日本語Get the appThe daily timetable, and why you may be missing it
Each flower opens in the late afternoon, usually within an hour or two of the temperature starting to drop, stays fully open through the evening and all night, and by mid morning has closed into a limp twist of color that falls off. Every bloom is a single night's work. A plant carrying two hundred flowers on Tuesday evening looks bare on Wednesday at noon, and the two hundred it opens on Wednesday evening are entirely new ones.
This is why people report a four o'clock that never flowers. If you only walk past the bed in the middle of the day, on your way out in the morning and back after dark, you will genuinely never see the plant in bloom. Go out at dusk on a warm evening and the same plant will be covered. Before troubleshooting anything else, look at the plant an hour before sunset.
The timing is a response to falling light and falling temperature rather than a clock. On an overcast, cool day the flowers open in the early afternoon and can still be open at midday the following day. In a heat wave they open later and close earlier. Plants in shade open noticeably earlier than plants in full sun a few feet away, which is worth knowing if you want the display to start before you sit down for the evening.
The scent follows the same schedule, and it is the main reason to grow the plant. It is strong, sweet and carries a surprising distance on still evening air. It is aimed at the long-tongued night-flying moths that pollinate the flowers, and on a warm evening you will see them working the plant at dusk.
| Time of day | What the plant is doing | What you see |
|---|---|---|
| Morning | Yesterday's flowers collapsing and dropping | Limp twists of color; plant looks green and flowerless |
| Midday | Nothing open | A plain leafy bush; this is when people conclude it does not bloom |
| Late afternoon | Buds swelling and unfurling as light and heat drop | Trumpets opening over roughly half an hour, earlier if overcast |
| Dusk to midnight | Full bloom and peak fragrance; moths working the flowers | The whole point of the plant |
| Overnight | Flowers stay open; pollination happens | Scent still detectable near the plant |
Plant it where you sit in the evening: beside a porch, a bench, a doorway you use after dark, or under a window you open at night. A four o'clock in a front bed you only see at midday on your way to work is the wrong plant in the wrong place, however well it grows.
When it really is not flowering
If you have checked at dusk and there is genuinely nothing, work through three causes in order. The commonest by far is nitrogen. A plant in rich soil or on a regular feeding program puts everything into leaf: large, dark, soft foliage and few or no buds. Stop feeding and it will usually start budding within three weeks.
The second is shade. Four o'clocks tolerate part shade and will grow perfectly well in it, but a plant getting less than about five hours of direct sun makes a tall, loose, leaning bush with sparse flowering. Moving it is not practical mid season; note the position and plant something else there next year.
The third is simply age. From seed, a plant needs to reach a fair size before it starts, and flowering usually begins about eight to ten weeks after germination, which in a cool summer can mean quite late. An overwintered tuber flowers considerably earlier than a spring-sown seedling because it starts the season with reserves already banked, and that difference is one of the strongest arguments for lifting and storing the tubers.
Mixed colors on one plant
A single four o'clock will often carry flowers of more than one color at the same time, and individual blooms can be split down the middle, flecked, or striped, with the pattern changing from one evening to the next. This is normal and is not a sign of stress, disease or a mixed-up seed packet. It is a genuine instability in the pigment genes of this species, and it is why the plant is a standard teaching example in genetics.
It also means seed saved from a particular plant will not reliably give the same color, and self-sown seedlings drift over the years toward the deeper, more dominant shades. If a particular color matters to you, propagate that plant by dividing its tuber rather than by saving its seed.
Flowering continues without a break from mid summer until the first frost, and no deadheading is needed to keep it going. The plant will not take a rest in high summer heat the way many bedding annuals do, which makes it one of the most reliable things in the garden through the hottest weeks.
What to write down
Note the date the first flower opened and the number of weeks since sowing or since the tuber was replanted. That single figure tells you next spring whether to start seed earlier indoors, and it makes the case for saving tubers concrete rather than theoretical.
Record roughly what time the flowers opened on a hot clear evening and on a cool overcast one, and note the colors each plant produced, including any that changed through the season. Together with the position of each plant, that gives you a real basis for deciding what to keep, what to divide, and where to put it next year.