Allamanda cathartica aka Golden Trumpet

Allamanda cathartica, or golden trumpet, is a tropical evergreen climber. It belongs to the dogbane family, Apocynaceae. Its native range spans Central and South America. In the wild, it grows beside rivers in rain forests. Gardeners grow it in warm regions and under glass elsewhere. It grows fast, forming a sprawling shrub or woody vine. Without support, it can stand about 6.6 feet (2 metres) tall. Climbing stems can reach 20 feet (6 metres) or more. RHS gives a mature climbing height of 26–39 feet (8–12 metres). Its listed spread is 8–13 feet (2.5–4 metres).

The green, round stems hold a milky sap. They twine around supports but may still need tying. Older plants can form several stems from the base. Their long shoots may have few side branches. The simple leaves feel thick and leathery, with a glossy surface. They grow in opposite pairs or whorls, often of four. Their narrow, pointed blades give the plant a dense green backdrop.

Bright yellow trumpets bloom from summer into autumn. White marks may show inside their throats. Flower clusters form at shoot tips and beside the leaves. RHS records blooms about 0.4 feet (0.12 metres) long. The flowers draw butterflies to the garden. Prickly seed pods follow the blooms and hold winged seeds. Growers can raise new plants from seeds or greenwood cuttings.

Give this plant full sun and shelter from frost. It needs moist, fertile soil that drains well. Loam or sand suits it, with acid to neutral pH. Very alkaline soil can cause leaves to turn yellow. It does not tolerate salty soil. Water needs are moderate, but the roots need steady moisture. Its USDA range is 10–11, and RHS rates it H1B. In colder regions, bring container plants indoors before frost. Choose a bright spot for winter growth.

Use it on fences, trellises, porches, or walls. Containers also suit patios, screens, and single accent plants. In tropical gardens, it can form hedges or ground cover. It may spread fast into abandoned fields and waste ground. Most plants stay free of disease, though leaf spot can occur. Watch for mites, whitefly, scale, and mealybugs.

No edible uses are known, and all parts contain toxic material. Eating it can cause nausea, diarrhea, and other signs of poisoning. The sap can irritate skin and eyes. It can harm people, dogs, and cats. Traditional medicine uses leaves and roots to purge the bowels or cause vomiting. These uses do not make the plant safe to eat.