Four O'Clock Care: Space, Water and Keeping a Shrub-Sized Plant in Bounds

Treat it as a shrub that dies back, not as a bedding annual

The seed is the size of a peppercorn and the seedling looks like nothing much, so it gets planted at bedding spacing. By late summer that plant is three to four feet (90 to 120 cm) tall and just as wide, with woody-based branches and a canopy dense enough to shade out everything under it. Nothing else grown from seed in a single season gets that big that fast, and the plants either side of it will have been smothered long before you notice it happening.

Plan on one plant filling a circle three feet (90 cm) across. In a bed that means 24 to 36 inches (60 to 90 cm) between plants and the same clearance from anything you care about. If you already have them crowded at 12 inches (30 cm), pull every other one out now rather than later; the survivors will fill the gap within a month and you will get better flowering from both halves of the row than from a solid hedge of half-starved stems.

Where the plant is perennial the tuber gets larger every year and the top growth gets correspondingly bigger, so a three-year-old clump can push past four feet (120 cm) in all directions. Give an established position more room than a first-year one, and expect to lift and divide eventually rather than letting one tuber take over the corner.

Water and feeding: less than you think on both counts

The tuber is a water store, and it makes the plant far more drought-tolerant than its soft, lush foliage suggests. An established four o'clock in open ground will go through two weeks of dry weather with nothing more than a slight dulling of the leaves and will not lose flowers over it. Water deeply once a week in a dry spell rather than lightly every day; a soaking that reaches the tuber six inches (15 cm) down is worth five sprinklings that wet only the surface.

Containers are the exception. A plant in a pot builds a tuber that quickly fills the container, and from mid summer onward a large plant in a 12 inch (30 cm) pot will need water every day in hot weather and sometimes twice. If a potted plant wilts before noon, it is rootbound rather than thirsty, and no watering schedule will fix that until it is moved into something larger.

Feeding is where most people go wrong. Four o'clocks flower well in poor, ordinary soil and respond to rich feeding by making an enormous mound of dark leaves with the flowers buried inside it. If yours is all foliage, stop feeding altogether for the rest of the season. One application of a balanced fertilizer in late spring is the most an in-ground plant needs, and in a bed that gets compost each year it needs nothing at all.

The whole plant, and especially the seeds and the tuber, is toxic if eaten. The sap also irritates some people's skin. Wear gloves when you cut it back or lift tubers, and if children collect the seeds, which they will because the black beads are appealing, make sure they know these are not to be eaten.

Keeping the shape without losing the flowers

Left alone, a four o'clock builds a rounded dome and then starts to splay, with the outer branches leaning outward from the weight of foliage until the middle opens up. You can head that off with one cut in mid summer: shorten the longest branches by about a quarter, cutting just above a pair of leaves. The plant breaks into new growth within a fortnight and flowers on that new wood, so you lose perhaps ten days of bloom and gain a plant that stands up for the rest of the season.

Do not shear the whole thing over like a hedge. The flowers come from the branch tips, and cutting every tip at once means a plant with no flowers at all for two weeks. Work through it selectively, taking the branches that are out of place and leaving the rest to carry on.

Deadheading for the sake of more flowers is unnecessary. The plant blooms continuously from mid summer to frost whether you pick the old flowers off or not. What is worth doing is removing the developing seeds, because a mature plant sets hundreds of them and every one that hits the ground will germinate the following spring. Run your hand along the branch tips once a week and strip the hard black beads before they drop.

1. Give each plant a three foot circle Mark out 36 inches (90 cm) around the crown and keep anything you want to keep outside that line. Thin crowded rows early, while the plants are still under a foot (30 cm) tall and easy to pull without disturbing their neighbors.
2. Soak weekly, not daily Put a hose at the base and let it run slowly until the soil is wet four to six inches (10 to 15 cm) down. Repeat once a week in dry weather. Containers are the exception and need checking every day once the plant is large.
3. Shorten the sprawl once, in mid summer Cut the longest third of the branches back by roughly a quarter, always just above a leaf pair. New shoots and new flowers follow in about two weeks. Wear gloves; the sap bothers some skin.
4. Strip the seed before it drops Once a week from mid summer, pull off the hard black seeds forming behind the faded flowers. This is the only reliable way to stop a carpet of volunteers appearing next spring under and around the plant.

What to write down

Record the final width of each plant and how far the nearest neighbor was, because next season's spacing decision depends entirely on that number and nobody remembers it accurately. Note also the date you shortened the branches and how long it took to come back into flower, so you can time that cut earlier or later next year.

Two other notes pay for themselves. Write down where each plant stood, since a self-seeded colony will come up in that exact spot next spring and you want to know whether that is welcome. And note the date of the first hard frost that blackened the foliage, which is the signal to lift tubers in a cold garden and is easy to miss by a week if you are not watching for it.