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black-spined agave (Agave macroacantha)

Agave macroacantha is an evergreen, succulent, clumping rosette plant that may have a very short stem and forms colonies through basal shoots. It is perennial; an individual rosette dies after flowering, while new rosettes usually continue growth from offsets.

LightAgave macroacantha takes full sun; in hot low-elevation areas, light shade or an east-facing position can be provided.
WaterSources differ on watering guidance: during summer growth it may be watered regularly or thoroughly after the growing medium dries, with water reduced in autumn and kept dry or nearly dry in winter; established blue-gray
TemperatureSources differ on the lower temperature limit, with about -6 °C reported, while Agave macroacantha is described as frost hardy. It is reported to rest in winter, and a specialist source reports a cold minimum of about -6
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black-spined agave illustration

Overview

Agave macroacantha is an evergreen, succulent, clumping rosette plant that may have a very short stem and forms colonies through basal shoots. It is perennial; an individual rosette dies after flowering, while new rosettes usually continue growth from offsets.

Origin and habitat

Agave macroacantha is native to Puebla and Oaxaca in Mexico, particularly northern Oaxaca and the area near Tehuacán in Puebla. It occurs naturally on dry, rocky or sediment-rich slopes and wasteland, as well as in grassland, woodland, tropical deciduous forest, and xeric scrub, and can grow in calcareous, saline-alkaline, or gypsum-rich soils. Its native environments are predominantly dry to very arid, and it is adapted to strong sunlight and drought.

Characteristics

Sources differ on mature size, placing height at about 40–60 cm and spread at about 50–150 cm. Growth is relatively slow and reaching flowering size takes years; the stiff, succulent leaves are generally linear to narrowly sword-shaped and blue-gray to gray-green, with potentially wavy margins bearing small brown teeth and a sharp terminal spine ranging from dark brown or gray to black. Sources differ in their descriptions of the flowers, which are borne on a tall, branched inflorescence and may be described as purplish green, glaucous green, or gray with red; flowering occurs from spring into summer. The fruit is a dark-brown, elongate, three-chambered capsule containing black seeds, and Agave macroacantha stores water in its leaves.

Light

Agave macroacantha takes full sun; in hot low-elevation areas, light shade or an east-facing position can be provided.

Watering

Sources differ on watering guidance: during summer growth it may be watered regularly or thoroughly after the growing medium dries, with water reduced in autumn and kept dry or nearly dry in winter; established blue-gray-leaved forms grown in the ground are best kept on the dry side to reduce rot risk. In winter, watering is indicated at intervals of 30–60 days.

Temperature and dormancy

Sources differ on the lower temperature limit, with about -6 °C reported, while Agave macroacantha is described as frost hardy. It is reported to rest in winter, and a specialist source reports a cold minimum of about -6 °C. It has strong heat tolerance, although bright shade or east-facing exposure is suitable in hot lowland desert areas.

Growing medium and mounting

Agave macroacantha needs a very fast-draining mix; for containers, cactus mix or a sandy, loose, gravelly medium can be used, along with a relatively wide container.

Feeding

It is reported that a low-nitrogen fertilizer can be applied during summer.

Propagation

Agave macroacantha can be propagated by seed or by separating basal shoots.

Common problems

Scale insects are reported as a possible pest, while disease is generally reported to be uncommon. Excess moisture is reported to increase the risk of rot, especially for blue to blue-gray-leaved forms after establishment. The plant tolerates drought and heat, but its cold tolerance depends on moisture conditions; it withstands colder conditions when dry than when wet, and severe frost should be avoided.

Identification

The most conspicuous identifying features are orderly rosettes of narrow, elongated blue-gray to gray-green leaves with strongly contrasting black terminal spines; mature plants can form dense clumps.

Photos

Agave macroacantha
📷 Stan Shebs · CC BY-SA 3.0 · source

Sources