Aloe broomii possesses the most extraordinary inflorescence in the entire genus Aloe. Where every other aloe displays its tubular flowers openly on the raceme, Aloe broomii hides them completely beneath overlapping bracts arranged like the scales on a serpent’s body — the flowers invisible to the eye, only the protruding stamens and stigmas betraying their existence. This unique structure, which gives the species its common name “Snake Aloe” (slangaalwyn), has no parallel in any other South African aloe and remains one of the most striking sights in the Karoo landscape when the tall, sinuous inflorescence rises above the rocky grassland in spring.
Beyond its morphological uniqueness, Aloe broomii holds a second, perhaps even more valuable, distinction for gardeners: it is one of the hardiest aloes on Earth. Brian Kemble’s records from the Ruth Bancroft Garden document a habitat minimum of 17 °F (–8.3 °C) — the second lowest of any aloe in the Kemble dataset, exceeded only by Aristaloe aristata. Growing naturally at altitudes of 1,000 to 2,000 m across the cold, arid interior of the Karoo, the species endures regular winter snow, hard frost, and wide diurnal temperature swings that would destroy almost any other aloe. For growers in cold-winter, dry-climate regions who have longed for an aloe that can survive outdoors year-round, Aloe broomii may be the answer — provided they can keep it dry.
Family: Asphodelaceae Subfamily: Asphodeloideae Genus: Aloe Accepted name (POWO): Aloe broomii Schönland, Records of the Albany Museum 2: 137 (1907) Infraspecific taxa: Aloe broomii var. broomii; Aloe broomii var. tarkaensis Verd. Common names: Snake Aloe, Mountain Aloe; slangaalwyn (Afrikaans)
Taxonomy and Nomenclature
Aloe broomii was described by Selmar Schönland in 1907 from material collected by Dr. Robert Broom in 1905 at Pampoenpoort, between Carnarvon and Victoria West in the Northern Cape. The species honors Broom (1866–1951), a British-born South African physician and paleontologist better known for his discoveries of hominid fossils at Sterkfontein and Kromdraai than for his botanical collecting, though it was his eye for interesting specimens that brought this aloe to scientific attention.
Varieties
Two varieties are recognized:
Var. broomii is the typical, widespread form: a short-stemmed, robust rosette with green leaves and dark reddish-brown marginal teeth, distributed across the central and western Karoo, Free State, and southern Lesotho. This is the plant most commonly available in the nursery trade.
Var. tarkaensis Verd. is a form from the Tarka area in the southeastern Eastern Cape, described as having broader, more glaucous (bluish) leaves and a somewhat more compact growth habit. Dave’s Garden contributors in Arizona have reported that var. tarkaensis performs better than the typical variety in hot, low-desert climates, possibly owing to its greater tolerance of intense solar radiation. Lavranos has suggested a taxonomic relationship between Aloe broomii and Aloe chlorantha, a yellow-flowered species from the southwestern Karoo, though this affinity has not been formalized.
Distribution and Ecology
Native Range
Aloe broomii is widespread across the interior plateau of South Africa, with a distribution centered on the Karoo and extending into adjacent highland regions:
- Northern Cape: from Prieska westward through Carnarvon, Victoria West, Beaufort West, and Murraysburg. This is the core of the species’ range, where the largest and densest populations occur.
- Eastern Cape: from Britstown eastward through Cradock, Graaff-Reinet, and the Tarka area (home of var. tarkaensis) to approximately Tarkastad.
- Free State: the central and southern Free State, including records near Luckhoff and extending into the Ficksburg area.
- Lesotho: southern districts, where the species reaches some of its highest altitudes.
- Limpopo: scattered records in the northernmost part of its range, representing a substantial disjunction from the main Karoo population.
The species grows at altitudes between 1,000 and 2,000 m, placing it firmly in the cold, frost-prone interior of the country. It is not a coastal species: unlike Aloe ferox, Aloe thraskii, or Aloe pluridens, Aloe broomii never approaches the sea.
The species is assessed as Least Concern on the South African Red List and is not threatened. Like all Aloe species except Aloe vera, it is listed on CITES Appendix II. Aloe broomii is depicted in 250-year-old rock paintings in South Africa, attesting to its long presence in the human cultural landscape of the Karoo.
Habitat and Ecology
Aloe broomii grows in Grassland, Nama Karoo scrub, and thornveld, typically on north-facing rocky slopes and ironstone ridges where drainage is sharp and exposure to winter sun is maximized. It favors calcareous (high-lime) soils over ironstone or dolomite substrates — an important cultural clue for growers (see Growing Conditions below).
The climate across its range is semi-arid continental — one of the most extreme faced by any cultivated aloe:
- Annual rainfall: 300 to 500 mm, concentrated almost entirely in summer (November to March). Winters are bone-dry.
- Summer temperatures: daytime highs of 30 to 38 °C, with warm nights.
- Winter temperatures: cold and severe. The Karoo interior regularly experiences hard frost, with minima of –5 to –10 °C not uncommon. Snow can lie for one to two weeks at the highest altitudes. Diurnal temperature swings of 20 to 30 °C between day and night are characteristic of clear Karoo winter skies.
This climatic profile — bitterly cold and dry in winter, hot and modestly wet in summer — defines the species’ cultural requirements with precision. Aloe broomii is adapted to cold, not wet: the combination that destroys it is not frost alone, but frost combined with wet soil.
Pollination ecology. The distinctive inflorescence, despite concealing its flowers beneath bracts, attracts a wide array of pollinators: bees, wasps, ants, and malachite sunbirds (Nectarinia famosa). The protruding stamens and stigmas ensure that pollinators access pollen and nectar even though the flower tube is hidden. Colonies of Aloe broomii provide a critical summer nectar resource on the Karoo flats, where few other plants flower during the spring and early summer.
Seed predation. The seeds are frequently parasitized by small maize and rice weevils (Sitophilus spp.), which leave characteristic round exit holes in the seed coat. This is a concern for growers collecting seed: inspect seeds before sowing and discard any with weevil damage.
Morphological Description
Aloe broomii is a robust, short-stemmed, acaulescent to very short-caulescent, evergreen succulent, reaching approximately 50 to 100 cm in height (rosette only) and up to 150 cm including the inflorescence. It is usually solitary but occasionally the growing point divides, producing groups of up to three (rarely five) rosettes.
Rosette and leaves. The rosette is dense, symmetrical, and may reach 80 to 100 cm in diameter. Leaves are lanceolate, approximately 30 cm long and 10 cm wide, thick and fleshy, light green to yellowish-green. The upper third of each leaf is often dry and brownish — a natural senescence pattern, not a sign of poor health. Leaf margins are armed with dark reddish-brown teeth that are characteristically curved along the outer edges of each leaf — darker and more prominent than the pale teeth of most other acaulescent aloes. The dark tooth color is a useful identification character. Leaf surfaces are smooth and unspotted.
Inflorescence and flowers — the signature feature. The inflorescence is a single (unbranched), erect, densely flowered raceme reaching 1.0 to 1.5 m in height above the rosette — imposing for a plant of this stature. Its most remarkable character is the complete concealment of the flowers behind oversized bracts. The bracts are broad, densely overlapping, arranged like tiles on a roof (imbricate), and completely enclose the buds and open flowers. The only visible evidence of flowering is the protruding stamens and stigmas that emerge beyond the bract tips. This gives the entire inflorescence a sinuous, scaly, serpentine appearance — hence “Snake Aloe.”
The flowers themselves are pale greenish-yellow, tubular, 20 to 25 mm long, opening in a band approximately 100 mm wide that ascends from the base of the raceme upward. No other South African aloe shares this floral architecture: Aloe broomii is morphologically unique within the genus.
Flowering period in the Southern Hemisphere is spring (September to October). In the Northern Hemisphere, flowering shifts to March to May — though growers in Arizona have reported flowering as late as September, suggesting the species can adjust its phenology substantially under cultivation.
Fruit and seeds. Dehiscent capsules containing winged seeds that are dispersed by wind but frequently parasitized by Sitophilus weevils.
Growth rate. Described as moderately fast under favorable conditions: llifle.com notes that plants can reach full size within 5 to 6 years if given appropriate soil, light, and seasonal moisture patterns.
Comparison with Two Cold-Hardy Aloes
Aloe broomii vs. Aloe polyphylla Schönl. ex Pillans (Spiral Aloe)
Both species are iconic, cold-hardy, high-altitude South African aloes that endure snow and hard frost in the wild. However, they differ dramatically in cultural requirements:
| Character | Aloe broomii | Aloe polyphylla |
|---|---|---|
| Distribution | Karoo interior, Free State, Lesotho | Drakensberg escarpment (Lesotho, Eastern Cape) |
| Altitude | 1,000–2,000 m | 2,300–2,600 m |
| Habitat | Dry rocky Karoo slopes, ironstone ridges | Wet, misty, foggy mountain summits |
| Annual rainfall | 300–500 mm (dry) | 1,500–2,000 mm (wet) |
| Cold hardiness (Kemble) | 20 °F (–6.7 °C) cult. / 17 °F (–8.3 °C) habitat | Mid-20s °F (~–4 °C) cult. / 9 °F (–12.8 °C) habitat |
| Wet tolerance | Poor — requires dry winter rest | High — requires constant moisture |
| Heat tolerance | Good (Karoo summers reach 38 °C) | Poor — suffers above 27 °C |
| Leaf arrangement | Dense, upright rosette | Famous spiral pattern |
| Inflorescence | Unique: flowers hidden by bracts | Branched, short racemes of pink to red flowers |
| Ease of cultivation | Moderate — needs dry winter, full sun | Difficult — needs cool, moist, airy conditions |
The critical point: despite their shared cold hardiness, these two species have opposite moisture requirements. Aloe broomii demands dry cold (Karoo winter); Aloe polyphylla demands wet cold (Drakensberg mist). A grower who succeeds with one will likely fail with the other unless growing conditions are adjusted accordingly.
Aloe broomii vs. Aloe claviflora Burch. (Kraalaalwyn)
Aloe claviflora is another cold-hardy Karoo aloe that shares much of Aloe broomii‘s range and ecological niche. Brian Kemble records it at 20 °F (–6.7 °C) in cultivation and 24 °F (–4.4 °C) in habitat, with the note “rots easily if wet too long, but hardy to 20°.”
| Character | Aloe broomii | Aloe claviflora |
|---|---|---|
| Growth habit | Dense, upright rosette; essentially acaulescent | Low, decumbent; stem grows horizontally |
| Rosette diameter | 80–100 cm | 30–50 cm (more compact) |
| Inflorescence | Erect, single, unbranched, 1–1.5 m; flowers hidden by bracts | Horizontal to angled, branched; flowers visible |
| Flower color | Pale greenish-yellow | Bright red to orange |
| Cold hardiness (Kemble) | 20 °F / habitat 17 °F | 20 °F / habitat 24 °F |
| Wet tolerance | Poor | Very poor (“rots easily if wet too long”) |
| Leaf color | Light green to yellowish | Grey-green to blue-green |
| Distribution | Northern Cape, Eastern Cape, Free State, Lesotho | Northern Cape (narrower range) |
Both species require essentially the same cultural conditions: full sun, alkaline mineral substrate, dry winter rest. The distinction is primarily aesthetic: the massive, upright rosette and hidden-flower inflorescence of Aloe broomii versus the low, sprawling habit and visible bright red flowers of Aloe claviflora.
Cold Hardiness: The Evidence in Detail
The cold tolerance of Aloe broomii is among the most thoroughly documented of any aloe, with data from multiple independent sources converging on a consistent picture.
Brian Kemble’s Data (Ruth Bancroft Garden, Walnut Creek, California, USDA zone 9b)
Cultivation minimum: 20 °F (–6.7 °C). Habitat minimum: 17 °F (–8.3 °C).
The habitat figure of 17 °F is the second lowest in the entire Kemble dataset (out of approximately 100 species tested). Only Aristaloe aristata has a lower habitat minimum (13 °F / –10.6 °C). The fact that the cultivation minimum (20 °F) is warmer than the habitat minimum (17 °F) suggests that Aloe broomii may tolerate even colder temperatures in the ground than it has been exposed to at the Ruth Bancroft Garden, provided conditions are dry — consistent with the species’ native environment, where winter temperatures routinely drop below –8 °C on the Karoo plateau.
Hardy Tropicals UK Forum
A UK grower reported growing Aloe broomii outdoors for three consecutive winters with no damage, using a plastic mini-greenhouse cover for rain protection. However, a second plant planted just a couple of feet away rotted — despite experiencing identical temperatures. The grower’s conclusion: “They are cold hardy but not so much wet hardy.” The plant that survived had been established longer (and therefore “hardened off”), while the one that died was more recently planted and presumably less acclimatized.
This report is highly informative because UK winters combine precisely the conditions that are most challenging for Aloe broomii: temperatures in the –3 to –8 °C range combined with persistent humidity and winter rain. The survival of the covered plant — protected from rain but not from cold — confirms that winter moisture, not cold per se, is the limiting factor for this species.
Dave’s Garden Forums
Aloe broomii is mentioned among Highveld species that “have to handle occasional snow (week or two) and frost” in their native habitat. It is listed alongside Aloe polyphylla, Aloe peglerae, Aloe pratensis, and Aloe striatula as a cold-hardy species from central South Africa. The implication is that it belongs to the hardiest tier of aloes, comparable in cold tolerance to the Drakensberg and escarpment species.
Agaveville Forum
An Arizona grower (Tempe, zone 9b, extreme summer heat) lists Aloe broomii among species they are “cautiously optimistic” about for in-ground cultivation, suggesting that while it has survived, its long-term performance in the extreme desert heat of Phoenix is not yet fully proven. Another grower photographed a magnificent flowering specimen at Boyce Thompson Arboretum in September — indicating that the species adjusts its flowering season under hot, arid cultivation conditions. The recommendation from Dave’s Garden that var. tarkaensis performs better than the type in low-desert climates adds a potentially useful provenance distinction.
Llifle.com / Other Sources
“Mature plants are said to handle snow, although younger plants should be protected from hard freezes and overly wet conditions.” This observation aligns with the general principle that aloe cold hardiness improves with age and acclimation. “It should be given a soil with a high lime content and grows best in those areas where there is frost in winter and the rainfall is not too high.” This is one of very few aloe care guides that explicitly recommends frost as a positive cultural factor — reflecting the species’ genuine adaptation to cold continental winters.
Synthesis: Where Aloe broomii Succeeds and Fails
Successes:
- In the ground in dry-winter climates (central and western South Africa, Arizona, inland California) with excellent drainage and full sun.
- In the ground in the UK under rain protection (plastic cloche, mini greenhouse) — confirmed by Hardy Tropicals UK grower for three consecutive winters.
- In containers overwinteried in unheated but dry shelters (cold frame, dry greenhouse) — temperatures can drop to –5 to –8 °C provided soil is bone-dry.
Failures:
- In the ground in wet-winter climates (UK, Pacific Northwest, coastal northern California) without rain protection — root rot, not cold, is the killer.
- Recently planted specimens that have not had time to acclimate — the Hardy Tropicals UK report of two plants in identical conditions, one surviving and one rotting, illustrates this.
- In humid subtropical climates (Florida, southeastern US) — the species is adapted to arid Karoo conditions and may struggle with persistent humidity.
The takeaway: Aloe broomii is one of the hardiest aloes in existence in terms of absolute temperature tolerance. Its Achilles’ heel is not cold but wet cold. In dry-cold climates (USDA zones 7b–8b with arid winters), it may succeed in the ground where virtually no other aloe survives. In wet-cold climates (UK, maritime northern Europe), success requires rain protection over the rosette and exceptionally well-drained, mineral-heavy substrate.
Optimal Growing Conditions
Light
Full sun, all day. Aloe broomii grows on exposed north-facing (sun-facing) rocky slopes in the Karoo and requires maximum solar exposure. In very hot climates (Arizona, inland California), some growers report that the species tolerates — but does not require — light afternoon shade. Insufficient light results in etiolated growth and failure to flower.
Temperature
Optimal growth occurs between 18 and 35 °C. The species is deeply adapted to wide diurnal temperature fluctuations and performs best in climates with warm days and cool nights. Cold tolerance is exceptional (see detailed analysis above):
USDA zones 8a to 11b for year-round outdoor cultivation in dry-winter climates. In zone 7b (–15 to –12 °C), the species may survive in exceptionally well-drained, south-facing, rain-sheltered microclimates — a frontier that deserves testing by adventurous growers.
Substrate
This is a critical factor. Aloe broomii grows naturally in calcareous (high-lime), sharply drained, rocky soils over ironstone or dolomite. In cultivation, provide a substrate consisting of 60 to 70% mineral aggregate (crushed limestone, dolomite chips, pumice, coarse grit) and 30 to 40% compost. The target pH is neutral to mildly alkaline (7.0–8.5) — more alkaline than the substrates preferred by most commonly cultivated aloes. Adding agricultural lime or dolomite flour to acidic potting mixes is recommended.
Avoid heavy, water-retaining soils. The species is far more sensitive to waterlogging than to cold, and root rot in wet substrate is the primary cause of death in cultivation.
Watering
Follow the Karoo rainfall pattern: generous summer watering, strict dry winter rest. During the growing season (spring through early autumn), water deeply every 7 to 14 days, allowing the substrate to dry between irrigations. From late autumn through winter (November to March in the Northern Hemisphere), reduce watering to zero if the plant is outdoors, or to a minimal monthly trickle if it is in a heated indoor environment. Never allow water to sit in the rosette during cool weather.
Fertilization
Minimal. The species grows naturally in nutrient-poor Karoo soils. An annual application of bone meal or slow-release balanced fertilizer in spring is sufficient. Excessive nitrogen promotes soft growth susceptible to rot.
Rain Protection
In winter-rainfall or year-round-rainfall climates (Mediterranean, UK, maritime northern Europe), overhead rain protection during the cool months is essential. Options include a transparent plastic cloche, a glass or polycarbonate lean-to shelter, or positioning the plant beneath deep eaves. The goal is to keep the rosette and root zone dry while allowing full light penetration and air circulation.
Propagation
Aloe broomii is propagated almost exclusively by seed, as the species rarely produces offsets (only when the growing point is damaged and the rosette divides).
Sow fresh seed in summer on a moist, well-drained, sandy medium. Treat seed with a systemic fungicide (metalaxyl-based, such as Apron C, as recommended by PlantZAfrica) to prevent damping-off, to which seedlings are particularly vulnerable. Cover lightly with 2 mm of sand. Maintain warmth (22 to 28 °C) and moisture; germination occurs within 2 to 3 weeks. Seedling growth is slow and vulnerable to overwatering and fungal attack. Prick out at 20 to 30 mm tall into a 2:1:1 mix of sand, loam, and compost.
Inspect seed before sowing for Sitophilus weevil damage (round exit holes in the seed coat). Discard damaged seed, as it will not germinate.
Ethnobotanical Uses
Aloe broomii has a documented history of veterinary use in the Karoo. In the Steynburg District (Eastern Cape), farmers employ the brownish fluid obtained from boiling the leaves as a tick repellent: a dessertspoonful of the boiled juice given orally to a horse temporarily renders the blood so bitter that any ticks on the animal fall off. The same preparation is used as a disinfectant, an ear remedy for sheep, and as a cattle dip. This ethnoveterinary application is unusual among aloes and has not, to date, been the subject of formal pharmacological study.
The species is not listed as toxic to people or pets.
Pests and Diseases
Aloe broomii is susceptible to aloe snout weevil (Rhadinomerus) and scale infestations, and to fungal root and crown rot — the latter being the primary cause of death in cultivation. Preventive measures include sharply drained substrate, dry winter rest, and tilting pots slightly so that water cannot accumulate in the rosette. In regions with high humidity, ensure good air circulation around the plant.
Bibliography
Carter, S., Lavranos, J.J., Newton, L.E. & Walker, C.C. (2011). Aloes. The Definitive Guide. Kew Publishing, Royal Botanic Gardens, Kew. 720 pp.
Kemble, B. (undated). “Brian Kemble’s List of Hardy Aloes.” Ruth Bancroft Garden / San Marcos Growers. Published online: smgrowers.com/info/brian_aloe.pdf
Pole Evans, I.B. (1936). “Aloe broomii (Liliaceae).” The Flowering Plants of South Africa 16: t. 605.
Reynolds, G.W. (1950). The Aloes of South Africa. Aloes of South Africa Book Fund, Johannesburg. 520 pp.
Schönland, S. (1907). “Aloe broomii.” Records of the Albany Museum 2: 137.
Van Jaarsveld, E.J. (2000). Wonderful Water-wise Gardening. Tafelberg, Cape Town.
Van Wyk, B.-E. & Smith, G.F. (2014). Guide to the Aloes of South Africa. 3rd ed. Briza Publications, Pretoria. 376 pp.
Authoritative Online Resources
- POWO — Plants of the World Online (Kew): Aloe broomii
- PlantZAfrica (SANBI): Aloe broomii species profile
- Red List of South African Plants (SANBI): Aloe broomii
- GBIF — Global Biodiversity Information Facility: Aloe broomii distribution data
- World of Succulents: Aloe broomii profile
- Gardenia.net — Aloe broomii: Snake Aloe
- Gardenia.net — Cold-Hardy Aloes: Landscaping guide
- Brian Kemble’s Hardy Aloe List (San Marcos Growers / Ruth Bancroft Garden): PDF
- Agaveville — Aloe broomii identification thread: Forum
- Hardy Tropicals UK — Hardy Aloes: Forum
- Llifle Encyclopedia of Succulents: Aloe broomii
- Cambridge University Botanic Garden: Aloe broomii