Hibiscus trionum aka Flower Of An Hour

Hibiscus trionum belongs to the mallow family, Malvaceae. Common names include bladder hibiscus and flower of an hour. Kew places its native range from east-central and eastern Europe to the Mediterranean and western Himalaya. Useful Tropical Plants notes that its original range is unclear. It now grows beyond cultivation across Europe, Asia and Africa. It occurs on worked ground and waste land.

This upright plant grows fast and forms many branches. Garden plants reach about 1.6–3.3 feet [0.5–1 metre] tall. RHS also describes plants reaching just 2 feet [0.6 metre]. Its spread can reach 1.6 feet [0.5 metre]. A strong taproot has thin side roots near the surface. The oval leaves have toothed edges. Gardeners grow it as an annual, though its lifespan can vary. Kew lists annual or biennial growth. In tropical climates, it may live as a short-lived perennial.

The flowers range from cream-white to pale yellow. Their dark centres have purple and brown tones. Each flower opens for a few hours, then wilts. This brief display explains the name flower of an hour. Missouri Botanical Garden lists flowering from June until frost. RHS gives late summer through early autumn for UK gardens. Insects pollinate the flowers. Swollen, bladder-like seed capsules follow the blooms. The flowers suit beds, borders, cottage gardens and containers.

Grow it in full sun in a sheltered spot. It prefers fertile soil with humus and good drainage. RHS lists sandy or loamy soil with acid or neutral pH. Medium watering meets its garden needs. Plant outdoors once the risk of frost has passed. RHS rates it H2, so it does not survive freezing. The USDA listing spans zones 2–11 for annual garden use. Raise new plants from seed; no pruning is needed. It can spread strongly by seed on bare, disturbed ground. Consider this weed risk before adding it to a garden.

Missouri Botanical Garden reports no major pest or disease problems. RHS lists possible powdery mildew and rare honey fungus. Under glass, aphids, scale, mealybugs and whitefly may attack it. Young leaves and shoots can be eaten raw or cooked. The root is edible but fibrous, bland and mucilaginous. Sources also record local food and medicinal use. These uses do not establish that every part is safe. Useful Tropical Plants warns that seed oil contains gossypol. It links ingestion with reduced sperm levels and male infertility.