Gadenin日本語Get the appThe toxicity is the hazard that matters most
Every part of the plant is toxic if eaten, and the seeds and the tuber are the most concentrated. The seeds are the practical risk: hard, round, black, about the size of a peppercorn, produced in the hundreds, and sitting at eye level for a small child. They look exactly like something to collect and put in a pot, and swallowing them causes stomach pain, vomiting and diarrhoea.
The tuber is the other risk. It is large, pale and fleshy, and a lifted one left in a shed or a bag can be mistaken for a root vegetable. Label anything you store. Dogs that dig will chew tubers, and the effect is the same as for people.
The sap causes contact dermatitis in some people. It is not dramatic, but if you are cutting back a large plant or dividing tubers you are handling a lot of cut tissue, so wear gloves and wash afterward. None of this is a reason not to grow the plant; it is a reason to strip the seeds before they drop and to be straightforward with children about it.
If someone has eaten seeds or root, contact a poison information service or a doctor and say the plant was Mirabilis jalapa. Take a piece of the plant with you. Do the same for a pet, with a vet.
What actually attacks the plant
Very little does serious damage. The foliage is unpalatable enough that deer and rabbits generally leave it alone, which alone makes it useful in gardens where nothing else survives. The problems that do occur are mostly cosmetic and mostly weather-driven.
Chewing beetles are the exception worth understanding. Some species, notably Japanese beetle where it occurs, will feed heavily on the foliage and shred the leaves into lace. The interesting part is that the foliage is toxic to them, so a four o'clock planted near roses or grapes can work as a trap plant, drawing beetles away from things you care about and killing a proportion of the ones that feed. If you use it that way, expect the four o'clock itself to look chewed by late summer and accept that as the cost.
Aphids build up on soft new growth in spring, especially on plants that have been fed. A hard jet of water every few days breaks the colonies up and predators finish the job; on a plant this vigorous, spraying is rarely justified. Slugs and snails go for seedlings and volunteers, and can clear a whole flush of them overnight, but they ignore anything more than a few inches tall.
| Problem | Early sign | What to do |
|---|---|---|
| Chewing beetles | Leaves skeletonised between the veins, adults visible in daylight | Hand pick into soapy water in the morning; accept damage if using it as a trap plant |
| Aphids | Sticky, distorted new shoot tips in spring | Jet of water every few days; stop feeding the plant |
| Spider mites | Fine stippling and dull bronze cast on leaves in hot dry spells | Water deeply, hose the undersides of leaves, raise humidity around containers |
| Leaf spot and rust | Brown or rusty spots on lower leaves after a wet spell | Remove the worst leaves, water at the base, thin the plant to move air through it |
| Slugs on seedlings | Volunteers vanishing overnight, slime trails on the soil | Only worth acting on for seedlings you want; larger plants are immune |
| Root knot nematodes | Stunted plant that wilts daily despite wet soil; lumpy roots | Do not replant four o'clocks in that spot; rotate the position |
Wet weather, dry weather and rot
In a humid summer the lower leaves pick up fungal leaf spots and sometimes rust. On a plant this dense it is nearly always an air movement problem rather than an infection you need to spray. Strip the worst of the lower leaves, shorten a few interior branches to open the middle up, and switch to watering at the base rather than over the top. New growth comes clean.
In hot dry weather the risk flips to spider mites, which show as a fine pale stippling and a dull, slightly bronze look to the leaf, with webbing in the leaf axils once it is advanced. Mites thrive on plants that are dry at the root and standing in still hot air, so a deep soak and a hard spray of water on the undersides of the leaves is both the treatment and the prevention.
The one genuinely fatal problem is tuber rot, and it happens in wet, heavy, poorly drained soil over winter and in storage. A tuber sitting in cold saturated ground turns soft and foul-smelling and the plant simply never comes up. If your soil stays wet in winter, lift the tubers rather than gambling on them, and check stored tubers monthly, throwing out any that have gone soft before the rot spreads through the box.
- Strip seed weekly through the season This handles the toxicity risk and the self-seeding at the same time. Run a gloved hand along the branch tips once a week from mid summer and pull off the hard black seeds behind the faded flowers.
- Open the plant up in humid weather Remove the lowest leaves and a few crowded interior branches so air moves through the middle. Water at the base only. This prevents most leaf spot without any spraying.
- Soak deeply in dry heat A weekly deep watering plus a hard hose on the leaf undersides keeps spider mites from establishing. Dry, stressed plants in still air are the ones that get infested.
- Check stored tubers monthly Look for softness, dark patches or any smell. Remove and discard affected tubers immediately; one rotting tuber will take the rest of the box with it over a couple of months.
What to write down
Note the date you first saw beetle damage and how long it lasted, because the feeding period is fairly consistent year to year and knowing it lets you plan hand picking rather than reacting. Note the same for the first leaf spot after a wet spell.
Also record which positions produced healthy plants and which produced stunted ones that wilted despite wet soil, since that pattern repeating in the same spot two years running points at nematodes or drainage rather than at anything you did. And record any tubers that rotted in storage, along with where they had been growing and how long you cured them, so you can adjust the drying time next season.