New Zealand Bittercress
Cardamine glara
Cardamine glara , also known as the New Zealand Bittercress or Glara's Cress, is a small, delicate herbaceous perennial endemic to New Zealand. This native cress is valued for its fresh, edible leaves and its ability to thrive in damp, shaded environments. It is a charming addition to shaded rock gardens, woodland edges, or as a groundcover in moist areas.
Plant Description
Cardamine glara forms small, spreading rosettes of bright green, deeply lobed leaves. The leaves are typically basal, arising from a short rhizome, and are often glossy. In spring and summer, slender flowering stems emerge, bearing clusters of small, four-petaled white flowers. These delicate flowers are followed by narrow, elongated seed pods (siliques) that, typical of cresses, can explosively dehisce to disperse their seeds. The plant remains relatively low-growing, usually reaching up to 10-20 cm in height.
Quick Facts
| Family | Brassicaceae (Mustard family) |
|---|---|
| Light | Partial to full shade |
| Soil | Moist, rich in organic matter, well-drained |
| Water | Moderate to high |
| Water Needs | High |
| Frost Tolerance | Hardy |
| Salt Tolerance | Low |
| Growth Rate | Moderate |
| Scientific Name | Cardamine glara |
| Height | 10-20 cm |
| Spread | 15-30 cm |
| Lifespan | Perennial |
Climate Best Suited to
Cardamine glara is a specialized alpine cress requiring cool, moist conditions typical of mountain screes and gravelly areas. Endemic to high-altitude regions, it needs excellent drainage combined with consistent moisture from snowmelt and rain. This species thrives in areas with cold winters, cool summers, and protection from hot, dry conditions.
Regional Suitability
| City | Climate Suitability |
|---|---|
| Whangārei | Unsuitable |
| Auckland | Unsuitable |
| Hamilton | Unsuitable |
| Tauranga | Unsuitable |
| Rotorua | Marginal |
| Gisborne | Unsuitable |
| New Plymouth | Marginal |
| Napier | Unsuitable |
| Whanganui | Unsuitable |
| Palmerston North | Marginal |
| Wellington | Suitable |
| Nelson | Suitable |
| Christchurch | Suitable |
| Dunedin | Ideal |
| Invercargill | Suitable |
Habitat
Natural Distribution
Cardamine glara typically grows in damp, shaded environments, such as forest floors, stream banks, and boggy areas. It prefers humus-rich, constantly moist soils and is often found in association with other shade-loving native plants. Its distribution is somewhat restricted, mainly found in parts of the South Island.
Conservation Status
Current Threats and Protection
Cardamine glara is classified as "Not Threatened" under the New Zealand Threat Classification System. However, like many native herbaceous plants, local populations can be vulnerable to habitat loss due to land development, draining of wetlands, and competition from invasive weed species. Conservation efforts focus on protecting and managing its specific damp, shaded habitats.
How to Grow
Cultivation Requirements
Cardamine glara is a relatively easy plant to grow in conditions that mimic its natural habitat. It thrives in partial to full shade and requires consistently moist, humus-rich, and well-drained soil. Incorporate plenty of organic matter, such as compost or leaf mould, into the planting area to improve soil structure and moisture retention. Regular watering is crucial, especially during dry spells. It is frost-hardy but appreciates protection from harsh winter winds and intense summer sun.
Planting Guide
Best Planting Practices
Plant Cardamine glara in spring or autumn in a shaded or semi-shaded location with moist, organic-rich soil. Dig a hole twice the width of the root ball and the same depth. Place the plant in the hole, ensuring the crown is at soil level. Backfill with enriched soil, firm gently, and water thoroughly. Apply a generous layer of leaf mould or fine bark mulch to help retain moisture and suppress weeds. Space plants 15-20 cm apart for groundcover.
Ecological Role
Environmental Benefits
Cardamine glara contributes to the biodiversity of New Zealand's forest floor ecosystems. Its small flowers provide a food source for native insects, and its spreading habit helps to stabilize soil in damp areas. As an edible cress, it also forms a small part of the local food web for foraging animals.
Uses
Traditional and Modern Applications
The fresh leaves of Cardamine glara are edible, offering a peppery, cress-like flavor. It can be used in salads, sandwiches, or as a garnish. In the garden, it is valued as an attractive groundcover in shaded, moist areas.
Landscaping Uses
Garden Design Applications
This delicate cress is ideal for shaded rock gardens, woodland gardens, or as an underplanting beneath trees and shrubs. It can be mass-planted to create a lush, green carpet in moist, shaded areas. Its low-growing habit and attractive foliage make it a charming addition to naturalistic native plantings.
Seasonal Care
Year-Round Maintenance
Cardamine glara requires consistent moisture, especially in spring and summer. Ensure it is protected from direct, hot afternoon sun. After flowering, the plant may go somewhat dormant or produce fewer leaves, but it typically revives with cooler temperatures and increased moisture. Remove any yellowing or spent foliage to maintain tidiness.
Pruning
Pruning Techniques
Pruning is minimal, primarily involving the removal of spent flower stalks after the flowers have faded to prevent excessive self-seeding, if desired. Trim any untidy or damaged foliage to maintain a neat appearance.
How to Grow New Zealand Bittercress
From Seed
Cardamine glara can be readily propagated from seed. Collect seeds in late summer after the slender seed pods (siliques) have ripened. Sow the fresh seeds onto a moist, well-draining seed-raising mix. Cover the seeds barely with a fine layer of compost or sand. Maintain consistent moisture and warmth (around 15-20°C / 60-68°F) in a protected, shaded environment. Germination typically occurs within a few weeks, and the plant can also self-seed readily in favorable conditions. Once seedlings are large enough to handle, prick them out into individual pots and grow them on in a sheltered, shaded location until robust enough for planting out.
From Division
Propagation by division of established clumps is an effective and common method for Cardamine glara. This is best done in autumn or early spring, just before new growth commences. Gently lift an established clump from the ground, taking care not to damage the delicate rhizomes. Carefully separate the clump into smaller sections, ensuring each division has healthy roots and foliage. Replant divisions immediately into their desired permanent positions or into pots filled with fresh, humus-rich, well-drained soil. Water thoroughly after replanting to help settle the soil around the roots and keep them consistently moist until established.
General Cultivation
New Zealand Bittercress is a relatively easy plant to grow in conditions that mimic its natural habitat. It thrives in partial to full shade and requires consistently moist, humus-rich, and well-drained soil. Incorporate plenty of organic matter, such as compost or leaf mould, into the planting area to improve soil structure and moisture retention. Regular watering is crucial, especially during dry spells and its active growth periods. It is frost-hardy but appreciates protection from harsh winter winds and intense summer sun. Plant in spring or autumn in a shaded or semi-shaded location. Dig a hole twice the width of the root ball and the same depth. Place the plant in the hole, ensuring the crown is at soil level. Backfill with enriched soil, firm gently, and water thoroughly. Apply a generous layer of leaf mould or fine bark mulch to help retain moisture and suppress weeds. Space plants 15-20 cm apart for groundcover.
Pests and Diseases
Common Problems and Solutions
Cardamine glara is generally robust and free from serious pests and diseases. The main issue is ensuring adequate moisture without waterlogging, as it can be susceptible to root rot in poorly drained soils. Slugs and snails may occasionally feed on its tender leaves.
Cultural Significance
Traditional Uses and Values
As a small but distinctive endemic plant, Cardamine glara contributes to New Zealand's unique botanical heritage. Its presence in damp, shaded forest environments reflects the rich biodiversity of these ecosystems. While specific traditional Māori uses may not be widely documented, it is part of the broader group of native plants that sustain the natural landscape.
Bonus Tip
Expert Growing Advice
Cardamine glara makes a delightful edible groundcover. Its peppery leaves can be harvested fresh for salads, adding a zesty native flavor to your culinary creations.
