Broom
Carmichaelia petriei
A leafless broom of open, stony river terraces and dry hillsides. Needs full sun, lean soils and excellent drainage; drought hardy once established. See more native shrubs .
Plant Description
Botanical Features
Carmichaelia petriei, known as Desert Broom, is a stout, upright shrub growing up to 2.5 meters tall. It is leafless, with thick, rounded, yellow-green stems (cladodes) that do the work of leaves. The branches are stiff and sparingly branched, giving it a somewhat architectural, skeletal appearance. It bears small clusters of purple and cream pea-flowers in summer, followed by persistent seed pods.
Quick Facts
Content for Carmichaelia petriei ( Carmichaelia petriei ).
| Scientific Name | Carmichaelia petriei |
|---|---|
| Height | 0.3-2 m (compact shrub) |
| Spread | 40-120 cm across |
| Water Needs | Low to moderate; free-draining soils |
| Light | Full sun |
| Frost Tolerance | High - tolerant of severe freezes |
| Salt Tolerance | Low to moderate |
| Growth Rate | Slow to moderate |
| Lifespan | Long-lived perennial |
Climate Suitability
Content for Carmichaelia petriei ( Carmichaelia petriei ).
| City | Climate Suitability |
|---|---|
| Whangārei | Suitable |
| Auckland | Suitable |
| Hamilton | Suitable |
| Tauranga | Suitable |
| Rotorua | Suitable |
| Gisborne | Suitable |
| New Plymouth | Suitable |
| Napier | Suitable |
| Whanganui | Suitable |
| Palmerston North | Suitable |
| Wellington | Suitable |
| Nelson | Suitable |
| Christchurch | Suitable |
| Dunedin | Suitable |
| Invercargill | Suitable |
Natural Habitat
South Island Interior
Endemic to the South Island, ranging from the Waitaki Valley and Mackenzie Basin down to Central Otago and Southland. It is a plant of dry, rocky places: river terraces, gorges, tussock grasslands, and montane scrub. It tolerates extremes of cold and heat, thriving in the semi-arid continental climate of the interior.
Conservation Status
Current Threats and Protection
Carmichaelia petriei is classified as "At Risk (Declining)" under New Zealand's threat classification system. Its populations face significant threats from browsing by introduced mammals (such as hares and rabbits), weed invasion, and habitat modification, particularly in its dryland ecosystems. Conservation efforts require active site protection, managing competing vegetation, and controlling animal browsing to support its long-term survival.
How to Grow
Cultivation Requirements
Carmichaelia petriei requires full sun exposure, sharp drainage, and low fertility soils to thrive. It is essential to avoid winter wetness around the crown, which can lead to root rot. Prune lightly after flowering to maintain a compact outline and encourage healthy growth, but avoid heavy cuts into old wood.
Planting Guide
Cultivation
One of the toughest native plants available. Plant in full sun in well-drained, dry soil. It tolerates poor fertility, rocky ground, and severe frost. It is not suitable for humid, shaded, or waterlogged sites. Excellent for planting in dry river beds, rock gardens, or as a structural element in a tussock garden.
Ecological Role
Dryland Specialist
It plays a role in the nitrogen cycle of dryland ecosystems, enriching the poor soils it inhabits. It provides shelter and perches for lizards and invertebrates in open tussock country. Notably, it is a host plant for the larvae of several native moths and potentially the rare fungus weevil Cerius otagensis.
Uses
Landscape Value
Used in landscape design for its unique, stark texture and "desert" aesthetic. It contrasts beautifully with the flowing foliage of tussock grasses (*Chionochloa* spp.). It is essential for ecological restoration in dry, degraded South Island high country environments.
Landscaping Uses
Garden Design Applications
Excellent for rock gardens, alpine collections, and naturalistic plantings. Best used in open, well-drained positions where its distinctive form can be appreciated. Combines well with other native alpine plants and provides year-round structure. Consider placement carefully due to sharp foliage - avoid high-traffic areas. Creates dramatic focal points in contemporary and native-themed garden designs.
Seasonal Care
Year-Round Maintenance
Spring management focuses on removing winter-damaged foliage and assessing drainage. Summer care emphasizes maintaining adequate moisture without waterlogging. Autumn preparation includes reducing irrigation and ensuring good air circulation. Winter protection may require covering in areas subject to excessive moisture. Year-round monitoring ensures early detection of problems and maintenance of optimal growing conditions.
Pruning
Maintenance
Minimal pruning is needed. You can tip prune young plants to encourage bushiness, but the natural open habit is part of its charm. Remove any broken or dead stems. It can be hard-pruned if necessary to rejuvenate an old plant, as it regenerates well from the base.
How to Grow Broom
From Seed
Carmichaelia petriei is best grown from seed. The seeds have a hard, impermeable coat that requires pre-treatment to ensure successful germination. Scarify the seed coat by gently rubbing it with sandpaper or by making a small nick with a knife, being careful not to damage the embryo. Alternatively, immerse the seeds in hot water (pour just-boiled water over them and let soak overnight as the water cools). Sow the pre-treated seeds in spring onto a free-draining seed-raising mix, covering them lightly with mix or fine grit. Maintain consistent moisture but avoid waterlogging. Germination can still be erratic, taking several weeks to months. Once seedlings are robust enough to handle, prick them out into individual pots and grow them on in a sunny, well-ventilated location until ready for planting out.
From Cuttings
Propagation from cuttings can be more challenging for Carmichaelia petriei due to its leafless nature and hard stems. However, it can be attempted with semi-hardwood material. Take cuttings of healthy, firm stems about 8-12cm long in late summer. Remove any soft growth from the tip and base, and treat the cut end with a rooting hormone. Insert the cuttings into a very free-draining mix of coarse sand and perlite. Place in a sheltered, well-ventilated environment with good humidity, but ensure excellent air circulation around the stems to prevent fungal issues. Rooting may take several months and success rates can be lower compared to seed.
General Cultivation
Petrie's Broom is one of the toughest native plants available, perfectly suited for dry, sunny, and exposed positions. It requires full sun, sharp drainage, and low fertility to thrive, mimicking its natural habitat on stony river terraces and dry hillsides. It tolerates poor fertility, rocky ground, and severe frost, making it an excellent choice for challenging sites. Avoid planting in humid, shaded, or waterlogged areas, as these conditions will quickly lead to root rot and plant demise. This broom is highly drought-hardy once established, requiring minimal supplementary water. Regular pruning is not generally required to maintain its low, compact outline; however, light tip pruning after flowering can encourage bushiness and denser growth. It is perfectly suited for a gravel garden, scree bed, or as a structural element in a tussock garden where its unique leafless form provides year-round interest.
Pests and Diseases
Common Issues
Generally very healthy. It can be attacked by browsing mammals (rabbits, hares, sheep) in the wild. In the garden, watch for lemon tree borer caterpillars which bore into the stems. Scale insects may occasionally be found but are rarely debilitating.
Cultural Significance
Botanical History
Named after Donald Petrie, a prominent early New Zealand botanist and educator who extensively documented the flora of Otago. The plant represents the stark, rugged beauty of the Central Otago landscape.
Bonus Tip
Structural Contrast
Use Carmichaelia petriei as a structural anchor in a dry gravel garden. Its stiff, upright yellow-green stems look fantastic when back-lit by the low winter sun, providing interest when other plants are dormant.
