Whip Broom (Carmichaelia flagelliformis) hero image

Whip Broom

Carmichaelia flagelliformis

Not Threatened

This native plant, known as Whip Broom (scientific name: Carmichaelia flagelliformis ), is a distinct shrub endemic to the North Island of New Zealand. Recognized for its slender, whip-like branches that often appear leafless, it is a fascinating example of New Zealand's unique broom flora. This comprehensive guide provides detailed information on its care, propagation, and importance within the New Zealand ecosystem. Understanding this plant contributes to the appreciation of our rich biodiversity and heritage, and supports conservation efforts for Native Shrubs .

Whip Broom (Carmichaelia flagelliformis) showing slender branches
Image credit: Whip Broom ( Carmichaelia flagelliformis ) - Photo via Wikipedia

Plant Description

Carmichaelia flagelliformis is an erect, stiff shrub typically growing to a height of 1-2 metres. Its name "Whip Broom" aptly describes its numerous slender, green branches which are often leafless or have tiny, inconspicuous leaves, particularly on mature plants. The branchlets are flattened or convex when young, becoming rounder as they age. In late spring to summer, it produces small, fragrant, purplish-lilac pea-like flowers in clusters (racemes) along the stems. These are followed by small, beaked seed pods containing red seeds mottled with black.

Quick Facts

Carmichaelia flagelliformis quick facts
Scientific Name Carmichaelia flagelliformis
Height 1 - 2 m
Spread 1 - 1.5 m
Water Needs Low
Light Full Sun
Frost Tolerance Hardy
Salt Tolerance Moderate
Growth Rate Medium
Lifespan Perennial

Climate Best Suited to

Carmichaelia flagelliformis is well-suited to a wide range of climates across New Zealand but naturally occurs in the North Island from East Cape southwards. It is hardy to frost and tolerant of dry conditions once established. It prefers open, airy environments and thrives in full sun. While it can tolerate some coastal exposure, it performs best in sheltered spots in extremely windy coastal zones.

Regional Suitability

City suitability for Whip Broom
City Climate Suitability
Auckland Suitable
Wellington Very Suitable
Christchurch Very Suitable
Dunedin Suitable
Queenstown Suitable
Invercargill Suitable
Hamilton Suitable

Plant Habitat

Native to the North Island, Carmichaelia flagelliformis is found from the coast to montane areas. Its natural habitats include river terraces, stream banks, rock outcrops, tussock grasslands, and the edges of forests and swamps. It is a pioneer species that often establishes in disturbed ground with shallow, poor, or stony alluvial soils, demonstrating its ability to thrive in challenging conditions.

Growing Requirements

Soil Requirements

Requires free-draining soil; tolerant of poor, stony, or sandy soils.

  • Sandy loam
  • Stony alluvium
  • Intolerant of waterlogging

Light Requirements

Demands full sun for best growth and flowering.

  • Full Sun
  • Light Shade

Water Requirements

Drought tolerant once established; water during dry spells in early years.

  • Low to Moderate
  • Avoid overwatering

Planting and Establishing

Plant Whip Broom in a sunny location with well-drained soil. It is particularly suitable for rockeries, banks, or mixed native borders. When planting, dig a hole slightly larger than the root ball and loosen the soil at the bottom. If the soil is heavy clay, incorporate grit or pumice to improve drainage or plant on a raised mound. Water well after planting and during the first summer. Avoid mulching heavily right up to the stem to prevent collar rot.

Ecological Role

As a member of the legume family (Fabaceae), Carmichaelia flagelliformis plays a beneficial role in the ecosystem by fixing nitrogen in the soil, which helps support surrounding plant growth. Its flowers provide nectar for native bees and butterflies, while the seed pods offer a food source for birds and insects. Its open, branching structure can also provide shelter for small fauna.

Uses & Significance

Garden Uses

Valued for its unique texture and form in native gardens.

  • Architectural specimen
  • Rock gardens
  • Dry, stony banks
  • Mixed borders

Ecological Value

Nitrogen fixer and pollinator support.

  • Soil improvement
  • Biodiversity support

Landscaping Uses

Carmichaelia flagelliformis offers a unique structural element to landscaping with its vertical, broom-like habit. It contrasts beautifully with broad-leaved shrubs like Hebe or Griselinia . It is an excellent choice for dry, difficult sites where other plants might struggle, such as steep banks or exposed, stony areas. Its delicate purple flowers add a subtle splash of colour in summer.

Seasonal Care Calendar

Spring

Inspect and feed.

  • Check for pests
  • Light prune if needed

Summer

Enjoy flowers.

  • Water young plants
  • Monitor for seed pods

Autumn

Planting season.

  • Plant new specimens
  • Collect seed

Winter

Dormancy.

  • Protect from waterlogging
  • Frost hardy

When to Prune and How Much

Carmichaelia flagelliformis requires minimal pruning. If the plant becomes straggly or too large, it can be lightly pruned after flowering to encourage bushier growth.

  • Prune after flowering
  • Avoid cutting into old wood

Removing dead or damaged branches improves the plant's appearance. Regular tip pruning of young plants can help establish a more compact habit.

How to Grow Whip Broom

Growing Carmichaelia flagelliformis is a rewarding experience for gardeners looking to add a unique, structural element to their native planting. This species is relatively easy to propagate and grow, provided its basic requirements for sun and drainage are met. It is a resilient plant that, once established, requires little maintenance. Propagation is most commonly achieved through seed, which is produced in abundance, or via semi-hardwood cuttings. Its ability to fix nitrogen makes it a self-sufficient feeder, often thriving in soils where other shrubs would fail.

From Seed

Seed propagation is the most natural and effective method. Seeds are housed in small pods that ripen in late summer to autumn.

Sowing fresh or scarified seed improves germination.

  1. Collect the seed pods when they turn brown and dry. Open them to remove the small, mottled seeds.
  2. To speed up germination, lightly scarify the seeds by rubbing them with sandpaper or soaking them in warm water overnight. This helps moisture penetrate the hard seed coat.
  3. Sow the treated seeds in a tray of free-draining seed-raising mix. Cover lightly with mix or grit.
  4. Keep the tray moist and in a warm, bright spot. Germination usually occurs within a few weeks.
  5. Prick out seedlings into individual pots once they have developed their first true leaves (which may be small leaflets) and are large enough to handle.

Grow the seedlings on in a sheltered nursery spot for their first winter before planting out in spring.

From Cuttings

Semi-hardwood cuttings can be taken in late summer or autumn. This method ensures the new plant is a clone of the parent, useful if propagating a particular form.

Cuttings require care to strike.

  1. Select healthy, semi-ripe stems about 10-15cm long.
  2. Remove any lower leaves (if present) and dip the cut end in rooting hormone powder or gel.
  3. Insert the cuttings into a pot containing a mix of sand and peat or perlite.
  4. Place in a warm, humid environment, such as a propagator or under a plastic cover, out of direct sunlight.
  5. Mist regularly to maintain humidity until roots develop, which can take several months.

Additional Methods

While seed and cuttings are the primary methods, ensuring the right planting site is the best "method" for long-term success.

Site selection tips:

  1. Choose a spot with maximum sun exposure.
  2. Verify drainage; dig a test hole and fill with water to see how fast it drains. If it sits, improve the soil or mound up.
  3. Allow space for the plant's upright, spreading habit.

Pests & Diseases

Carmichaelia flagelliformis is generally robust but can be susceptible to the lemon tree borer (*Oemona hirta*), the larvae of which tunnel into stems causing dieback. Pruning off affected branches is the best control. Scale insects and aphids may occasionally infest new growth; these can be treated with neem oil or simply blasted off with a hose. Root rot can occur in heavy, waterlogged soils, emphasizing the need for good drainage.

Cultural Significance

The genus Carmichaelia is named after Dugald Carmichael, a Scottish botanist who collected plants in New Zealand. While specific traditional Māori uses for this exact species are not widely documented compared to other plants like Harakeke, the brooms as a group are a characteristic component of the New Zealand landscape, particularly in open, dry areas.

  • Characteristic NZ flora
  • Ecological pioneer

Bonus Tip

Plant Whip Broom near a pathway where you can brush past it; the stiff stems make a pleasing rustling sound, and the small flowers release a sweet scent on warm days.

Plant Conservation

Carmichaelia flagelliformis is currently classified as "Not Threatened" under the New Zealand Threat Classification System. However, like many native plants, it faces pressures from habitat modification and introduced pests. Protecting its natural habitat from clearance and maintaining healthy populations in the wild ensures its continued survival.