Firespike (Odontonema tubaeforme)

Firespike has clusters of small and tube-like flowers with nectar that bees and birds feed on. This plant can be easily maintained since it can grow both in partially shady and partially sunny areas, but it may look like it’s dying on the ground in extreme weather conditions in winter. However, it grows back in the spring.

I. Appearance and Characteristics 

Odontonema tubaeforme is a plant in the family Acanthaceae. The genus name “Odontonema” refers to the toothed filaments of the stamen, nema meaning “thread” and odonto “toothed”. In English this species is known as cardinal flower, cardinal’s guard, or fire spike.

It is native to Central America, but has naturalised in several countries as an ornamental garden plant, including New Zealand and Australia. Since 2005 it has been recorded in the wild in the far north of New Zealand, at Auckland, Kaitaia, and Doubtless Bay. In New Zealand it usually spreads through the dumping of garden waste, although in one locality (Cooper’s Beach) seedlings have been found. In the Pacific it is considered an invasive species, and has recently naturalized in Rarotonga and Mangaia in the Cook Islands.

O. tubaeforme is an upright shrub up to 2 m or 3 m tall. Its elliptical, glossy leaves are 10 cm by 20 cm with a 2 cm petiole and arranged opposite each other on the stem. It has terminal spikes of waxy red to burgundy flowers, 30 mm long with 5 mm petals, and blooms in summer and autumn. It is grown as an annual frost-tender ornamental garden plant.

II. Types of Firespike Plants

The genus Odontonema is native to the New World, including 20 to 30 species distributed in Mexico, Central America, South America, and the Caribbean. Firespikes are listed as “benign” when referring to their toxicity.2 Closely related species include:

• Odontonema callistachyum: Also called purple firespike, it’s native to Mexico and Central America, growing 6 to 8 feet tall with spikes of lavender-purple flowers appearing summer through late winter or year-round, depending on the climate.
• Odontonema brevipes: Shrub from Trinidad and Tobago, growing primarily in the wet tropics.
• Odontonema laxum: Found in Ecuador in subtropical or tropical moist lowland forests.
• Odontonema nitidum: Also called shrubby tooththread, it’s native to Cuba, Haiti, Leeward Is., Myanmar, Trinidad and Tobago, and the Windward Islands.

III. How to Grow and Care

Sunlight

Firespikes love sunshine. Naturally found in tropical environments, these plants thrive in bright light.

Unlike most plants, firespikes will still bloom in the shade. However, more sunshine is best for more blooms and a healthier plant.

Temperature and Humidity

Native to Mexico and Central America, these plants love hot weather and moderate to high humidity. Firespikes are very hardy when it comes to hot temperatures but not so much with cold temperatures.

It can survive in areas with a light frost, but heavy frost will kill it. In areas with a light frost, you will see blooms in late summer until the frost comes. For areas without frost, your firespike could bloom all year long.

Watering

Keeping your firespike well-watered is essential because these plants depend on plenty of moisture. Keep it consistent and water daily if you live in a dry area. If you forgot for a day or so and see the plant wilting, don’t panic. Firespikes are moderately drought tolerant. Firespikes are hardy, and most bounce back after watering.

Keeping a layer of mulch on the soil around your plant will help retain moisture and keep the soil from drying out too quickly.

Soil

This plant isn’t fussy when it comes to soil pH levels. For optimum growth, however, firespikes like rich, well-draining soils. Sandy soils will also be tolerated. Compost-based soil is an excellent option for extra nutrients to keep your firespike healthy and blooming.

Fertilizing

This plant is easy-going and doesn’t need any specific fertilizers. Although, you can give it a general, well-balanced, slow-release fertilizer. Fertilize once in the spring to encourage fresh, healthy growth and blooms. Fertilize up to three times yearly or monthly during the growing season with a weakened liquid fertilizer.

Pruning

If your firespike blooms all year round, only occasionally prune side branches along the edges that can get long, unruly, or gangly looking. Prune it with size and shape in mind.

For firespike plants that produce seasonal flowers, perform a hard cutback on mature plants down to 12 to 18 inches tall with hand pruners in the spring. Do not use shears. Another hard cutback can be done in October, but do not prune after October, or it might affect the winter bloom.

Propagation

This easy-to-care-for plant is also straightforward to propagate from cuttings, best done in the spring. Here’s how:

• You’ll need pruners, a potting medium, and optionally, a clean pot, and rooting hormone.
• Trim a 4- to 5-inch clipping off of a healthy, softwood branch ending with a few leaves.
• Trim leaves off of the bottom half of the cutting.
• Dip the cut end into the rooting hormone.
• Plant with the cut side down in a container or in the ground where you want your new plant to grow.
• Plant firespike 2 1/2 to 3 feet apart and 3 feet from the house, walkway, or driveway.

How to Grow From Seed

Firespike plants produce few viable seeds. This species is mainly propagated by vegetative reproduction.

Potting and Repotting 

These shrubs can be grown in outdoor containers but get easily stressed during transplantation, so when finding a container, ensure it’s suitable for the plant’s lifespan.

When growing firespike in outdoor containers, it will require more frequent watering. Smaller firespike varieties can be grown indoors in 10- to 14-inch pots. A larger, deeper 24-inch container should suffice for bigger plants grown outdoors.

Overwintering

This shrub does best in USDA zone 10 and 11. In cooler zones, it will die. Bring it indoors during colder weather to overwinter the plant in cooler zones.

If inground in a zone where frost is rare but predicted, cover the firespike bushes to protect them. If the plant gets frostbite, the aboveground growth will die but will grow back in the spring when the soil warms.

Pests and Diseases

Common Pests & Plant Diseases

This plant is resistant to most common pests or diseases, including nematodes. However, firespike is irresistible to deer.

Occasionally, firespike can get mealybug infestations. To rid the plant of mealybugs, dab 70% isopropyl alcohol using cotton swabs along the surfaces of the plant. Test a small section of the plant first to ensure it doesn’t harm the leaves.

Common Problems

Once established, firespike is an easy-to-care-for plant. It can tolerate a light frost but will die in a wintery weather zone.

Drooping

Firespike needs regular water, or else it will start drooping. Give it good watering to help bring it back to vibrancy.

Floppy, Scraggly Overgrowth

Although this plant can grow in the shade, it will get leggy and scraggly with lanky overgrowth. Put this plant in a full or partial sun location. When this shrub gets “floppy” around the edges, cut off side branches to keep it looking trim.

Breaking, Damaged Branches

Firespike is susceptible to wind damage since its branches are delicate. Put this plant in a location with wind protection to prevent limb breakage.