Botanical Name: Allamanda cathartica
Origin: The Golden Trumpet Vine originates from Brazil.
Height: Not pruned, this house plant can reach heights of up to 2.4 m (8 ft). Dwarf varieties grow up to 38 cm (15 in) in height.
Soil: Allamanda cathartica can be planted in any high quality potting mix.
Light: Golden Trumpets need plenty of bright light, including a minimum of 4 hours worth of direct sunlight per day.
Humidity: This tropical plant requires moderate to high (50 per cent and upwards) levels of relative humidity. Levels can be raised using a humidifier or a wet pebble (humidity) tray.
Temperatures: The frost-tender Allamanda does not like to be cold in any way, although it will tolerate winter temperatures down to 16 degrees C (60 degrees F). Ideal temperatures for this house plant range, however, between 18 and 27 degrees C (65 to 80 degrees F).
Water: Golden Trumpet plants need to be watered thoroughly, allowing the top layer (5 cm/ 2 in) of potting mix to dry out between watering sessions. Drainage trays must be emptied immediately to prevent the soil getting soggy.
Fertiliser: Allamanda cathartica needs to be fed with a high-potassium - diluted (50:50) - liquid fertiliser on a bi-weekly (every two weeks) basis, starting in spring and on into autumn.
Propagation: Early spring is the best time to take and root (in moistened soil) Golden Trumpet stem tip cuttings (8 to 10 cm/ 3 - 4 in long). Using a heat mat will produce the best results.
Description and Care Tips
Like the pink-flowered Mandevilla, the Golden Trumpet belongs to the Apocynaceae family, which is also commonly known as the Dogbane family. Similar to other members of this family, the Golden Trumpet has a milky sap that is considered to be poisonous (likely to cause serious skin irritations). In addition, all of its parts are cathartic, meaning they induce accelerated evacuation of the bowel.
The stunning beauty of this tropical twining vine does, however, make the effort of wearing gloves while handling the plant well worth it.
The whorled, leathery and deeply veined leaves of Allamanda cathartica are bright green - ranging into light green - and, combined with the plant's twining habit, make this a highly attractive plant at the best of times.
The main attraction of Allamanda cathartica, however, are its stunning, 7.5 to 10 cm (3 to 4 in) wide, trumpet-shaped flowers. Typically bright yellow in colour (although there are now some varieties featuring creamy coloured flowers), these magnificent blooms gradually unfold from the scrolled flower buds that emerge from the plant's stem tips in summer. Blooming lasts from summer right through into autumn.
Some Golden Trumpet cultivars have been specifically bred to provide beautiful fragrances. One of these cultivars features darker leaves than the original species and brown, furry buds.
To grow and bloom well, Allamanda cathartica needs to be given plenty of bright light. The plant can be moved outside (into a semi-shaded position) during the summer to increase its blooming power. It must, however, be returned to a sunny spot inside before temperatures are likely to drop below 16 degrees C (60 degrees F), as it does not tolerate being cold.
Golden Trumpets can be trained to grow up and through a supporting trellis, which will really show off its spectacular flowers. If size needs to be controlled, this house plant can be pruned back by as much as half its size in early spring.
In addition to keeping the size under control, this pruning will also encourage more flowers, as will cutting off spent blooms.
Spring is also a good time to repot the plant. As Allamanda cathartica grows well in comparatively large containers, it can be repotted into pots a size larger than the previous year every spring. Naturally, it is important to use containers with drainage holes to prevent soggy soil.
After the plant has flowered, it will produce prickly seed pods, from which - when the pods have dried and break open - winged seeds will emerge and fly about. Although Allamanda cathartica is an evergreen, its growth will slow as winter approaches, and the plant should be given a winter rest.
While it is important to keep this tender plant at room temperatures, watering should be reduced slightly - though not enough to allow the potting mix to completely dry out.
Both aphids and mealy bugs do, by the way, like to make a meal out of this house plant, so it is important to look out for and immediately treat infestations.