Tuberose (Agave amica)

Fragrant, showy flowers in late summer lead many to plant tuberose bulbs. Polianthes tuberosa, which is also called the Polyanthus lily, has a strong and enticing fragrance that furthers its popularity. Clusters of large white blooms form on stalks that can reach 4 feet (1 m.) in height and rise from grass-like clumps. Keep reading about the care of tuberose flowers in the garden.

I. Appearance and Characteristics 

Agave amica, formerly Polianthes tuberosa, the tuberose, is a perennial plant in the family Asparagaceae, subfamily Agavoideae, extracts of which are used as a note in perfumery. Now widely grown as an ornamental plant, the species is native to Mexico.

The common name derives from the Latin tuberosa through French tubéreuse, meaning swollen or tuberous in reference to its root system.

The tuberose is herbaceous, growing from underground tubers of tuberous roots. It produces offsets. The leaves are a dull green and about 1–1.5 ft (30–50 cm) long and up to 0.5 in (13 mm) wide at the base. They are slightly succulent. The inflorescence is a spike, reaching up to 3 ft (1 m) high, with pure white waxy flowers. The flowers are tubular, with a tube up to 2.5 in (6 cm) long, separating into six flaring segments (sepals) at the end, and are strongly fragrant. There are six stamens, inserted into the tube of the flower, and a three-part stigma.

The double-flowered cultivar ‘The Pearl’ has broader and darker leaves, and shorter flower spikes, usually reaching only 1.5–2 ft (50–60 cm). Orange-flowered forms of the species have been reported. As well due to crossing with other species there are now yellow, pink, red and greenish forms.

The species was first described for science by Carl Linnaeus in 1753, as Polianthes tuberosa. In 1790, Friedrich Kasimir Medikus moved the species to the genus Tuberosa as Tuberosa amica. Both morphological and molecular phylogenetic studies have shown that Polianthes is embedded within the larger genus Agave, and the genus is now included in a broadly circumscribed Agave. Two incorrect attempts were made to name the species when transferred to Agave. In 1999, Joachim Thiede and Urs Eggli published the name “Agave tuberosa”.

However, Philip Miller had published this name in 1768, for the species now called Furcraea tuberosa, so it cannot be used again, and Thiede and Eggli’s name is illegitimate. In 2001, Thiede and Eggli published a replacement name (nomen novum), “Agave polianthes”. However, since Medikus’s Tuberosa amica is considered to be a synonym of Polianthes tuberosa, its epithet is the second oldest and according to the International Code of Nomenclature for algae, fungi, and plants should be used when the older epithet is unavailable.

Hence Thiede and Eggli’s second name is superfluous, and the correct name for the species within Agave is Agave amica, as was explained by Thiede and Rafaël Govaerts when they published this combination in 2017.

Tuberoses can be overwintered outdoors in hardiness zones 8-10. In colder zones, tuberoses are grown as summer annuals, in pots or mixed-flower borders where they can be enjoyed for their scent. To flower the plants require around 4 months of warm temperatures from the time the rhizome is planted. Gardeners usually start the rhizomes in pots in greenhouses beginning in late-winter or early spring, moving them outdoors in late spring once frost danger has passed. If they are started directly in the ground at this time, they may not bloom until September, greatly reducing the period in which their blooms may be enjoyed. Once the foliage begins to yellow in October, the leaves should be clipped, the rhizomes dug and stored in a cool, dry and dark place for the winter.

II. How to Grow and Care

Sunlight

In order to reach their full flowering potential, tuberose plants need a lot of sunlight. That said, these plants don’t like to dry out quite as much as other succulents or types of agave. For a healthy tuberose, plant yours in a spot that receives sun most of the day.

In hotter climates, consider giving your plants some shade in the afternoon. If they get six to eight hours of exposure early in the day, a bit of shade in the afternoon will help to keep them hydrated. A layer of mulch around the base of the plant can also help to retain some moisture in the soil.

Temperature and Humidity

Tuberose is native to a hot and humid climate. It thrives in environments with tropical conditions and is not highly cold-tolerant. If you mulch heavily in the fall, your tubers should survive temperatures as low as 0° to 10°F (-18° to -12°C) over the winter months. This makes them fine for planting in zone 7, but any colder and your tubers won’t survive the winter.

These plants are fully cold hardy in zone 8 and have no issues tolerating temperatures in the range of 10° to 20°F (-12° to -7°C). The foliage is very heat tolerant, but the flowers are less so. In temperatures higher than 95°F (35°C), expect your flowers to wither and fade fast. Supplemental water can help in very hot weather.

Your tuberose will appreciate a normal to high level of humidity. These do not make very good houseplants as they prefer hot, humid weather. They can survive indoors, but they are unlikely to bloom.

Watering

These plants are drought tolerant, but not to the extent that some others like it are. Your tuberose plant will tolerate dry weather, but if you want it to bloom well, water it occasionally. Don’t allow your plant to bake in hot, dry soil, or your flowers will fade very quickly.

If you experience drought during the growing season, you’ll need to water your plant. Give this plant about one to two inches of water per week. It’s important to not over-water this plant. The tuberous roots are vulnerable to fungal rot. Sitting in soggy soil will rot the roots and ultimately kill the plant.

Soil

First and foremost, tuberose plants need well-draining soil. Their tuberous roots will rot if they remain wet for a long time. These are not the right plants for swampy soil. They need a lot of nutrients, so their soil should be rich in organic matter.

Sandy soil is good for these plants. However, it will need some amending with organic compost or manure to provide the nutrients this plant requires. Loose, loamy soil is ideal, and a slightly acidic pH will keep this plant happy. A pH in the range of 6.0-6.5 is great. It’s better to err on the side of being too acidic rather than alkaline. 

Fertilizing

This is a moderate to heavy-feeding species. If you want it to look its best, you’ll need to fertilize. At the beginning of the season, apply a slow-release, granular fertilizer.

For flowering, give your plant a fertilizer that is higher in phosphorus. A 5-10-5 formula is a good place to start.

During the growing season, fertilize your tuberose every four to six weeks. You can also mix some well-rotted compost or manure with your soil at planting time. This will break down slowly, providing your plant with a low level of nutrients for an extended period.

Propagation

Tuberose plants are easy to propagate because of the way their roots grow. Like most tuberous plants, you can simply dig up the bulbs and divide them. Separate your bulbs every three to four years to keep them from crowing each other and to promote better flowering. You should do this even if you’re not looking to propagate.

Gently use a garden fork to loosen the soil and lift your tubers out of the ground. Split the bulbs apart and choose the largest bulbs to replant. These are great plants to share with other plant lovers.

Pests and Diseases

• Common Pests 

While pests will typically choose other garden plants to feed on, tuberose isn’t completely pest-proof. You may experience issues with bud borers and grasshoppers. Diatomaceous earth is a good defense against bud borers. Sprinkle it on the ground immediately surrounding your plant.

Deter grasshoppers by using a grasshopper bait or plant a trap crop of tall grass-like plants. Once grasshopper populations have taken off, the best way to deter them is to give them something else to eat. Then, handpick them or destroy the trap crop.

• Common Diseases 

While pathogen issues are not limited to fungal diseases, these are the most common issues with this plant. Fungal diseases, including root and crown rot, are common in tuberose plants. The issue stems from poor drainage or overwatering. These plants are very sensitive to overwatering.

Poor air circulation is another culprit of fungal disease, especially on leaves. This is a problem in humid climates more than in drier ones. Make sure that there is proper air circulation around your plant, and only water when the surface of the soil is dry. Planting in a location with proper drainage is vital for this reason.

Maintenance

Maintenance pruning is an ongoing task during the growing season. If you notice yellowing or brown leaves, feel free to trim them off. Do the same for any leaves damaged by disease or pest infestation.

Deadheading your tuberose is important if abundant flowers are your goal. The more you cut the flowers from the plant, the more it will produce. Whether you cut them for a bouquet or leave them on the plant until they wither, remove them. You will be glad you did!

In terms of fall pruning, wait until the first frost kills off the foliage before pruning. In warm climates that don’t experience frost, wait until the weather is cool. Then, cut the foliage down to about six inches tall. Make sure to apply a heavy layer of mulch in climates that experience freezing weather.

III. Uses and Benefits 

• In perfumery

The overwhelming fragrance of the tuberose has been distilled for use in perfumery since the 17th century, when the flower was first transported to Europe. French Queen Marie Antoinette used a perfume called Sillage de la Reine, also called Parfum de Trianon, containing tuberose, orange blossom, sandalwood, jasmine, iris and cedar. It remains a popular floral note for perfumes, either in stand-alone Tuberose fragrances or mixed floral scents, but it generally must be used in moderation because the essence is overpowering and can become sickly to the wearer.

• Other uses

In India and Bangladesh they are widely used in making flower garlands which are offered to the gods or used as wedding ornaments.

While once associated with funerals, it is now used in floral arrangements for other occasions.

In Indonesia, tuberose flowers are also used in cooking.

In Hawaii, they are one of the main flowers used in the construction of leis. Some others are plumerias, ginger, orchids, and pikake (jasmine).