Corrugated Broom

Carmichaelia corrugata

At Risk - Declining

Introduction

Overview

Corrugated Broom ( Carmichaelia corrugata ) is a unique leafless native shrub characterized by its distinctive grooved, photosynthetic stems that create an unusual architectural appearance. This remarkable adaptation allows the plant to photosynthesize through its green stems rather than traditional leaves, making it perfectly suited to dry, rocky environments. Endemic to New Zealand's Canterbury region and classified as At Risk - Declining, this species represents an important conservation priority while offering distinctive ornamental value for specialized native gardens.

Carmichaelia (Carmichaelia corrugata) showing its distinctive features in natural habitat — Image credit: Corrugated Broom (*Carmichaelia corrugata*) - Photo by Wikipedia contributors, via Wikipedia

Corrugated Broom is a distinctive, low-growing leafless shrub native to the dry river terraces and rocky slopes of New Zealand's South Island. It forms a dense, springy mat of grooved, yellow-green branches. In spring and summer, it produces small, pea-like pink flowers with attractive dark purple centres. This hardy plant is perfectly adapted to survive in poor, dry soils and is an excellent choice for rock gardens and other dry, sunny spots among New Zealand's native shrubs .

Quick Facts

Table data
Scientific Name	Carmichaelia corrugata
Common Name	Corrugated Broom, Common Dwarf Broom
Family	Fabaceae
Height	2-8 cm
Spread	Up to 1 m
Water Needs	Low, drought tolerant
Light	Full sun to partial shade
Frost Tolerance	Hardy
Salt Tolerance	Moderate; tolerates coastal conditions
Growth Rate	Moderate
Lifespan	Long

Climate Best Suited to

White maire (Nestegis lanceolata) is primarily found in lowland to hilly forests across the North Island of New Zealand, extending to the Marlborough Sounds in the South Island. It demonstrates good adaptability to various conditions, thriving in areas with well-drained soils and tolerating both full sun and partial shade. Its natural distribution suggests a preference for warmer, more humid environments but with a reasonable tolerance for cooler temperatures found in its southern range.

Regional Suitability

City suitability for White maire
City	Climate Suitability
Whangārei	Ideal
Auckland	Ideal
Hamilton	Ideal
Tauranga	Ideal
Rotorua	Ideal
Gisborne	Ideal
New Plymouth	Ideal
Napier	Ideal
Whanganui	Ideal
Palmerston North	Ideal
Wellington	Ideal
Nelson	Ideal
Christchurch	Ideal
Dunedin	Moderate
Invercargill	Moderate

Natural Habitat

Distribution and Environment

Understand the natural habitat of Corrugated Broom ( Carmichaelia corrugata ), including its geographical distribution, preferred environmental conditions, and the types of ecosystems where it thrives. This knowledge is crucial for replicating its natural growing conditions in cultivation.

Geographical distribution in Canterbury and Central Otago.
Preferred dry river terrace and rocky slope conditions.
Typical associated plant communities in dryland ecosystems.

Plant Conservation

Carmichaelia corrugata, also known as common dwarf broom, is classified as "Threatened - Nationally Vulnerable" under the New Zealand Threat Classification System. This status was assigned in 2018 and reaffirmed in 2023.

Previously, the species was assessed as "Not Threatened" in 2004 and 2008, and then as "At Risk - Declining" in 2012. It is endemic to the South Island of New Zealand.

Growing Requirements

Soil Requirements

White maire (Nestegis lanceolata) is remarkably adaptable to different soil conditions, thriving in well-drained environments. It can tolerate a variety of soil types, from sandy to loamy, and prefers a neutral to slightly acidic pH. Good drainage is crucial to prevent root rot, ensuring healthy growth and development.

Tolerates a wide range of soil types from clay to sandy
Prefers well-draining soils but can handle occasional waterlogging
Thrives in moderately fertile soils but will grow in poor soils too
Can tolerate slightly acidic to slightly alkaline pH
Handles coastal conditions including salt spray

Light Requirements

White maire (Nestegis lanceolata) thrives in a variety of light conditions, from full sun to partial shade. Optimal growth and flowering are typically achieved in locations receiving ample sunlight throughout the day. However, it can also tolerate some shade, especially in hotter climates, where it benefits from protection during the most intense afternoon sun.

Full sun for optimal growth and form
Can tolerate partial shade but may develop a leggier form
At least 6 hours of direct sunlight daily is ideal
Northern or eastern exposures work well in garden settings

Water Requirements

Once established, White maire (Nestegis lanceolata) is remarkably drought-tolerant, requiring minimal supplemental watering. During its establishment phase, consistent moisture is crucial to encourage strong root development. Mature plants can withstand dry periods, but regular watering during prolonged droughts will promote healthier growth and more abundant flowering.

Moderate watering during establishment (first 1-2 years)
Drought-tolerant once established
Can handle periods of soil saturation
Reduce watering in winter when growth slows
Signs of overwatering include yellowing leaves and crown rot

Planting Guide

Best Time to Plant

Plant in spring or autumn to allow the plant to establish its root system during milder weather.
Choosing a Location

Choose a sunny, open site with very well-drained, poor soil. It is perfect for a rock garden, gravel garden, or a dry, sunny bank.
Planting Steps

Dig a hole that is no deeper than the root ball but twice as wide. Gently place the plant in the hole and backfill with the original soil. Water lightly. Do not add rich compost or fertilizer to the planting hole.

Ecological Role

Carmichaelia corrugata plays a vital ecological role in New Zealand's dryland and open shrubland ecosystems. As a nitrogen-fixing legume, it significantly contributes to soil fertility, making it a crucial pioneer species for stabilizing dry slopes and alluvial soils. Its unique branch architecture provides essential habitat and shelter for various native fauna, contributing to biodiversity and supporting complex food webs. The plant's resilience and ability to thrive in harsh conditions make it an important component of ecological restoration projects.

Uses and Significance

Garden Uses

Specimen tree for visual impact
Suitable for native gardens and restoration projects
Enhances native garden aesthetics and biodiversity
Provides architectural accent with its unique structure
Effective for erosion control on slopes and banks

Ecological Value

Ecologically, White maire (Nestegis lanceolata) plays a crucial role in supporting native ecosystems. Its fruits are a food source for birds, especially the kereru, contributing to the local biodiversity and food web.

Provides a vital food source for native birds, especially the kereru
Offers habitat and nesting sites for various fauna
Contributes to soil stabilization and nutrient cycling
Forms natural shelter belts, protecting other species

Landscaping Applications

Design Integration

Discover how Corrugated Broom ( Carmichaelia corrugata ) can be effectively integrated into various landscaping designs. This section offers creative ideas and practical advice for using this unique dryland shrub to enhance the beauty and functionality of your outdoor spaces, from residential gardens to public parks.

Design ideas for rock gardens and xerophytic landscapes.
Best uses in gravel gardens and Mediterranean-style plantings.
Combining with other dryland natives for aesthetic appeal.

Seasonal Care Calendar

Spring

In spring, White maire (Nestegis lanceolata) begins its active growth phase. New foliage emerges, and it's an ideal time for planting new specimens or propagating. Ensure adequate moisture and monitor for early signs of pests.

New growth begins with fresh foliage development
Apply a balanced, slow-release fertilizer if desired
Excellent time for planting new specimens or dividing offsets
Monitor for new pest activity and address promptly

Summer

Summer is the peak growing season for White maire (Nestegis lanceolata), often accompanied by flowering. Consistent watering is important, especially for young plants, to support vigorous growth and prevent stress during dry periods.

Flowering typically occurs in early to mid-summer (November-January)
Water young trees regularly during extended dry periods
Avoid heavy pruning during the active growing season

Autumn

During autumn, White maire (Nestegis lanceolata) prepares for the cooler months. Fruits or berries develop, providing food for native birds. It's also a good time for planting and general garden cleanup.

Fruits or berries develop and ripen (December-February), attracting birds
Natural leaf shedding occurs as part of its growth cycle
Good time for planting new specimens to establish before winter
Clean up fallen leaves if a tidy appearance is desired

Winter

Winter is generally a dormant period for White maire (Nestegis lanceolata). Minimal care is required, though young plants may benefit from protection in colder regions. This is an opportune time for any necessary structural pruning.

Generally dormant with minimal growth activity
No special winter protection needed in most mild climates
Suitable time for structural pruning if required
Fallen leaves can be left as mulch or removed for tidiness

When to Prune and How Much

White maire (Nestegis lanceolata) generally requires minimal pruning to maintain its natural form and health. Pruning should focus on removing dead or damaged growth and shaping the plant as needed.

Remove dead, damaged, or diseased branches at any time of year
Light formative pruning when young helps establish good structure
To create a multi-trunked specimen, cut the main stem to encourage branching
Fallen leaves can be removed for a tidier appearance, or left as natural mulch
If necessary, lower branches can be removed to create clearance underneath
Major pruning is best done in late winter to early spring before new growth

Always use clean, sharp tools for pruning to minimize the risk of disease and ensure clean cuts. The plant often responds well to pruning with vigorous new growth, contributing to a fuller, healthier appearance.

How to Grow Corrugated Broom

From Seed

Difficulty: Moderate

Corrugated Broom ( Carmichaelia corrugata ) is most reliably raised from seed. Collect ripe pods in late summer to autumn; the small, hard seeds are typical of New Zealand brooms (Fabaceae) and benefit from scarification to improve water uptake. Either nick the seed coat gently with a file, or pour hot (not boiling) water (~80°C) over the seeds and leave to soak for 12-24 hours until swollen. Sow into a very free-draining seed-raising mix and cover lightly (2-3 mm). Maintain bright light, excellent airflow and temperatures of 15-22°C; keep the medium evenly moist but never wet. Germination generally begins within 2-6 weeks but can be staggered. Prick out seedlings promptly into individual tubes to protect the developing taproot. Because Carmichaelia species form nitrogen-fixing symbioses, using a native-friendly mix or incorporating a small amount of local soil can help early rhizobia nodulation and vigorous growth. Harden off gradually and plant out in full sun with very sharp drainage: conditions that mirror the speciesâ natural dry river terraces and stony ground in eastern South Island regions.

From Semi-Hardwood Cuttings

Difficulty: Challenging

Cutting propagation is feasible but slower and with lower strike rates than seed. Take firm semi-hardwood cuttings 6-8 cm long from healthy current-season shoots in late spring to late summer. Reduce any small side shoots at the base, retain a minimal tuft at the tip, and make a clean basal cut just below a node. Dip bases in a rooting hormone (IBA 0.3-0.8%) and insert into a very free-draining medium such as 1:1 perlite and coarse sand. Provide bottom heat around 18-22°C and high humidity without prolonged leaf wetness; good ventilation is important for this leafless, cladode-bearing genus to limit fungal issues. Keep the medium just moist. Rooting can take 8-12+ weeks; pot on carefully into a gritty, well-drained mix and harden off in bright light. Establish outdoors only into full-sun, free-draining sites: overwatering or poorly drained soils are the most common causes of losses.

Pests and Diseases

Corrugated Broom ( Carmichaelia corrugata ) is generally a very hardy plant with excellent natural resistance to most pests and diseases, adapted to survive in challenging conditions.

Common Pests

Browsing animals: Rabbits and hares can damage plants in the wild
Generally pest-free: Most garden pests avoid this tough, low-growing plant

Common Diseases

Root rot: The main threat, caused by excessive moisture and poor drainage
Fungal issues: Rare, but can occur in humid conditions with poor air circulation

Environmental Stressors

Overwatering: Can be fatal, especially in winter
Poor drainage: The most common cause of plant failure

The key to success with Corrugated Broom is providing excellent drainage and avoiding overwatering. Once established in suitable conditions, it is extremely resilient.

Cultural Significance

Corrugated Broom (Carmichaelia corrugata) was used by Māori for various purposes. The tough, flexible stems were used for weaving and construction, and the plant also had medicinal uses in rongoā (traditional Māori medicine).

Bonus Tip

Nitrogen Fixation and Ecological Benefits

Like many legumes, Corrugated Broom is a nitrogen-fixing plant. This means it has a symbiotic relationship with bacteria in its root nodules that convert atmospheric nitrogen into a form usable by plants. This natural process enriches the soil, making it a valuable pioneer species for improving soil fertility in degraded or poor soils, and an excellent choice for ecological restoration projects.