Century plant

Identification and origin

Agave americana belongs to the family Asparagaceae. It is native to Mexico, from the north of the country to the Gulf coast, and to Arizona and Texas. It has naturalized in many warm regions, especially around the Mediterranean and in the Canary Islands.

It is a stemless perennial succulent that forms a tight rosette of thick, fleshy, smooth leaves, gray-green to blue-green. The long, spoon-shaped leaves reach 6 ft in length and 3–6 in in width; their edges carry spiny teeth, and each ends in a hard terminal spine at least 1 in long. In the ground the rosette reaches 6–10 ft tall and as wide; grown in a container, it usually stays around 3.5–5 ft. Growth is slow.

Despite an old belief, it does not take a hundred years to bloom: flowering comes after roughly ten to twenty-five years. A single stalk then rises from the center of the rosette, like a telephone pole branching near the top, reaching 15–29.5 ft and carrying tubular, greenish-yellow flowers 3–4 in long in summer. Oval brown capsules follow. The rosette that bloomed then dies, but offsets, or pups, form at its base and carry on.

Among the cultivated forms, ‘Marginata’ has leaves edged with broad bright yellow bands, var. mediopicta ‘Alba’ has a white central stripe, and ‘Yellow Ribbons’ has yellow stripes. The variegated forms are less cold hardy than the species.

Light

Century plant wants full sun, at least six hours of direct light a day, ideally from the south or east. Strong light is what keeps the rosette compact and gives it its blue color: in shade it stretches and loses its shape.

Indoors, give it the sunniest window in the house. If winter light falls short, fluorescent tubes hung 6–12 in above the plant and run fourteen to sixteen hours a day make up the difference well. When you move it outside in spring, get it used to direct sun gradually.

Watering

Century plant stores water in its leaves and tolerates drought for long periods; too much water is its main enemy. During active growth, water moderately but thoroughly, until water runs out of the drainage holes, then empty the saucer after a few minutes. Wait until the mix has dried well below the surface before watering again: push a finger into the mix to check.

Avoid small, frequent sprinklings, which distort growth. In winter, as days shorten and the plant goes dormant, keep it nearly dry, giving only enough water to keep the leaves from shriveling. That cool, damp season is exactly when rot sets in. Increase watering in spring as light returns.

Potting mix

Use a cactus and succulent mix, or make a very free-draining blend of one part potting mix, one part coarse sand, and one part fine gravel or pumice. Equal parts potting soil and coarse sand also work; the blend is right if a moistened handful crumbles after you squeeze and release it. The pH can be acidic to neutral.

The pot must have drainage holes, because standing water rots the roots quickly. During active growth, feed with a balanced liquid fertilizer diluted to half strength, no more than every two to three weeks. Avoid overfeeding, especially in winter, when short days, low light, and cool temperatures put the plant at rest.

Temperature

For good growth, century plant likes days around 64–70 °F and nights above 55 °F; it handles summer heat up to 100 °F without trouble. Heat combined with high humidity encourages disease, however, so keep the air moving.

In a container, bring it in before frost to a bright, cool room, a sunroom, or a cold greenhouse, and don’t let it drop below 41 °F: it cannot survive being frozen. Planted out in dry, well-drained ground, it is grown in USDA zones 8a to 11b, where it tolerates heat, wind, and salty seaside conditions.

Repotting

Century plant grows slowly and does best slightly underpotted: a container that is too large holds too much moisture around the roots. Repotting is therefore infrequent; do it in spring or fall and take the chance to remove offsets.

Protect yourself first: heavy gloves and long sleeves prevent puncture wounds and contact with the irritating sap. Use a clean pot with drainage holes and fresh, fast-draining mix, then water sparingly. Plan for the weight, too: a large potted plant is heavy to move.

Pruning

No pruning is needed. Simply remove dried lower leaves when they become unsightly. If children or pets move around the plant, you can clip off the hard spine at the tip of each leaf; in the garden, plant it at least 6 ft from walkways. After flowering, the mother rosette dies, and the pups at its base take over.

Propagation

The easiest method is to remove the offsets that form at the base of the plant, in spring or fall. Choose a pup that already has its own roots, detach it from the mother plant, and pot it in the usual mix in full light.

If a pup comes away without roots, let the cut surface air-dry, then set it on barely moist, sterile sand and water sparingly; pot it up once roots have formed. The flower stalk sometimes produces small plantlets that can be detached and potted. Growing from seed is possible but slow: it often takes more than a year to get a decent-sized plant.

Common problems

• Crown or root rot: overwatering, a mix that won’t drain, a pot without holes, or a winter that is too wet.
• Stretched rosette with long leaves: too little light, often made worse by frequent watering.
• Disease in hot, humid weather: stagnant air; improve air circulation and let the mix dry.
• Scale and mealybugs: small shells or cottony clusters; dab them off with a cotton swab dipped in rubbing alcohol.
• Agave snout weevil: the main pest of agaves in the garden.
• Slugs and snails: damaged leaves on plants grown outdoors.
• Rosette declining after a flower stalk: the species’ natural life cycle; keep the pups.

Any one symptom can have several causes: always check light, watering, temperature, and the condition of the roots together.

Toxicity

The plant has low toxicity. Its leaves and sap contain calcium oxalate crystals; if eaten, it is harmful to dogs and cats. On skin, the sap can cause painful, long-lasting contact dermatitis, so wear gloves and long sleeves when handling it. The terminal spines can also cause injuries. Keep it out of reach of children and pets, and if any is swallowed, contact a veterinarian or a poison control center.