How to Grow Allamanda Indoors

Flower of Golden Trumpet New Caledonia

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Allamanda is not a typical houseplant—it's a decidedly tropical plant that needs significant warmth and moisture to thrive during the summers. It's a loose climber that benefits from support, although it can be grown as a small shrub. It has a rapid growth rate and is typically planted in the spring. While there are varieties that have been treated to remain small, Allamanda plants tend to be fairly large. In their natural environment, they grow into largish shrubs.

There's one excellent reason to grow Allamanda indoors: their flowers. These plants, especially the Allamanda cathartica variety, feature large buttery yellow flowers with a brown throat and an intoxicating fragrance that hide among large, glossy leaves. When the plant is in full bloom, it's likely to be covered with these four-inch flowers and will be the pride of your collection.

Botanical Name Allamanda cathartica
Common Name  Allamanda, golden trumpet, common trumpetvine, yellow allamanda
Plant Type Evergreen 
Mature Size  10-20 ft. tall, 3-6 ft. wide
Sun Exposure Full, partial
Soil Type  Well-drained 
Soil pH  Acidic 
Bloom Time  Summer, fall
Flower Color  Yellow
Hardiness Zones  10-11 (USDA)
Native Area  South America
Toxicity Toxic to people and pets 

Allamanda Care

Allamanda is not a very forgiving plant in the home environment. Plants that are exposed to cold drafts or denied adequate water tend to drop leaves with impunity. Also, they will not bloom unless there's adequate warmth. For these reasons, many people in colder latitudes reserve Allamanda for the greenhouse or conservatory.

The most dangerous period for Allamanda cultivation is winter when even warm houses tend to become exceedingly dry. In these cases, it's essential to mist your plant frequently to help it keep its leaves—dropping leaves is not a good sign or a sign of natural growth cycles.

Light

Allamanda prefers strong light, including some direct sun. They can be adapted to full sun, or they can be grown successfully in an east-facing window with only a few hours of the morning sun. Adequate sunlight is essential for blooming.

Soil

A rich, peat-based potting soil with excellent drainage is beneficial.

Water

Water liberally throughout the summer, making sure your growing pot has good drainage. It's also helpful to mist every other day or so to provide adequate humidity. In the winter months, reduce watering, but don't let the plant dry out and make an effort to keep the root ball warm.

Fertilizer

Feed with a weak liquid fertilizer throughout the growing season. Cut fertilizer back to once a month or so in the winter.

Is Allamanda Toxic?

All parts of the Allamanda plant are toxic to humans, pets, and livestock, although the poisoning is not typically very severe. Coming into contact with Allamanda can cause skin and eye irritation that goes away after a few minutes. Ingesting the plant can lead to diarrhea, vomiting, thirst, and fever.

Allamanda Varieties

There are more than a dozen species of allamanda, but the most common one in cultivation is the Allamanda cathartica. This plant is sometimes called the golden trumpet and is a common landscape plant in subtropical and tropical regions. These are a few popular varieties within this species:

  • 'Grandiflora' is certainly grand, with stunning large yellow flowers.
  • 'Hendersonii' features redbuds and golden-colored flowers.
  • 'Flore Pleno' is a lovely showy plant with double white flowers.
  • 'Williamsii' boasts eye-catching trumpet-like double yellow flowers that bloom year-round but has a poisonous milky sap.

Propagating Allamanda

Allamanda roots readily from stem tip cuttings. To have the best chance of success, take the cutting early in the growing season from a fresh green shoot. Use a rooting hormone for the best chances of success and pot the cutting into a fresh pot of seed-starting soil. Place the cutting in a warm, humid environment with bottom heating and wait for new growth to emerge before potting out into a larger container.

Repotting

Repot Allamanda in the spring when new growth emerges—this is also a good time to take cuttings. When you repot, place it into a larger pot and provide some support if necessary. Allamanda can be grown as a low shrub, but it does best if allowed to grow up a simple support and trail slightly. This seems to show off its blooms to maximum effect.

Common Pests/Diseases

Allamanda is somewhat vulnerable to pests, especially aphids and mealybugs. Keep your eyes peeled for signs of infestation, such as damaged leaves, and treat at the first indication. Treat with insecticidal soap every week or so until the insects are no longer there.