Acaena (Acaena inermis 'Purpurea')

Overview

The striking Acaena inermis ‘Purpurea’ offers exceptional textural contrast with its low, dense mat of fern-like, purplish foliage. This low-growing herbaceous perennial, often called Acaena, excels as a durable ground cover where many other plants struggle due to poor soil or intense sun. The cultivar ‘Purpurea’ is specifically sought after for maintaining this rich, bronzy-purple coloration throughout the growing season.

While blooming with small white flowers in summer, the true ornamental value of Acaena inermis ‘Purpurea’ lies in its evergreen structure and its ability to thrive under challenging conditions like drought and shallow soils. It spreads readily by layering, quickly forming an attractive carpet perfect for softening hardscape elements.

Gardeners value this Acaena for its extremely low maintenance requirements once established, making it a workhorse plant in rock gardens or difficult border edges. Always verify local regulations, as some species of Acaena have invasive potential outside their native New Zealand range.

Fast Facts

• Plant Family: Rosaceae
• Plant Type: Herbaceous perennial
• Hardiness Zones: USDA Zones 5-9
• Size at Maturity:
  • Height: 1-2 ft
  • Spread: 1.5-3 ft
• Bloom Time: June to August
• Bloom Description: White
• Sun Exposure: Full sun
• Water Needs: Dry
• Maintenance Level: Low

How to Grow

For best establishment of Acaena inermis ‘Purpurea’, plant in the spring or fall. This species demands full sun for the most vibrant purple leaf color, though it can tolerate some light afternoon shade in very hot climates. When planting, incorporate sharp drainage; while it prefers evenly moist, sandy, well-draining soil, it is remarkably tolerant of poor, shallow, and rocky conditions.

Water sparingly once established, reflecting its ‘Dry’ water needs. This Acaena is highly drought-tolerant once its root system is developed. Fertilization is rarely necessary, aligning with its low maintenance profile. In colder areas near the border of its hardiness range (Zones 5-6), the foliage may die back during persistent freezes, requiring a light cleanup in early spring.

Propagation is straightforward, achieved easily through division of the creeping masses in spring. Be aware that Acaena spreads rather quickly, so plan its placement carefully. If unrestricted, this ground cover can become quite aggressive, necessitating containment or regular trimming to maintain garden paths or borders.

Landscape Uses

The mat-forming habit of Acaena inermis ‘Purpurea’ makes it an ideal ground cover, particularly effective in filling gaps between paving stones where it can handle light foot traffic. Its low stature, rarely exceeding a couple of inches in height but spreading wide, positions it perfectly at the front edge of mixed borders, preventing run-on from taller perennials.

Consider planting this Acaena in alpine settings or rock gardens, allowing it to cascade softly over stone edges. The deep purple foliage creates stunning color contrast against gray slate or lighter colored retaining walls. Pair it with plants that share its preference for sharp drainage, such as Sedums, Thymes, or low-growing ornamental grasses.

Because Acaena spreads effectively, use it to cover large, dry, sunny slopes where mowing is difficult. Gardeners should be mindful that planting this ground cover requires commitment to monitoring its spread, as noted by the invasive warnings associated with some Acaena species.

Standout Features

Flower Qualities

• Insignificant

Fruit Qualities

• Showy

Noteworthy Characteristics

Acaena inermis, commonly called New Zealand burr or sheep’s burr, is a low-growing herbaceous to semi-evergreen perennial native to open, grassy, montane and subalpine areas of New Zealand. This mat-forming ground cover will reach up to 2” tall and spread to fill a 2’ area. The compound leaves reach around 1” long and are almost fern-like in appearance, made up of small, toothed leaflets. The foliage can range in color from green to bronzy-purple. In summer, globular clusters of small, white flowers are held above the foliage and mature into showy, red, burr-like seed heads. The seeds are not armed with barbs at the end and will not stick to clothing or animals as readily as other species.The genus name Acaena comes from Greek and means “thorn”, in reference to the barbed seeds of many Acaena species.The specific epithet inermis means “spineless” or “having fewer spines”, in reference to the spininess of the seeds of this species compared to other closely related of Acaena.The common name refers to the native range of this species.‘Purpurea’ is a purple-leaved selection of Acaena inermis. Besides the leaf color, it has similar characteristics to the species.

Tolerances

• Deer
• Drought
• Dry Soil
• Shallow-Rocky Soil

Potential Problems

This variety is noted for having no major pest or disease problems of note, making its care relatively simple. Overwatering or planting in heavy clay soils where drainage is poor represents the greatest risk. Saturated roots can lead to rot or decline, especially during cool seasons. Ensure good airflow and avoid excessive summer irrigation to maintain the health of your Acaena inermis ‘Purpurea’.

Frequently Asked Questions

What hardiness zones is Acaena suitable for?

This tough cultivar, Acaena inermis ‘Purpurea’, is hardy across USDA Zones 5 through 9, offering reliable perennial performance across a wide climatic range.

How large does Acaena grow?

This ground cover typically maintains a height of 1 to 2 feet, spreading outwards to cover an area between 1.5 to 3 feet wide, forming a dense mat.

What sun exposure does Acaena inermis ‘Purpurea’ need?

For the best purple coloration and growth habit, this Acaena requires full sun exposure in most gardens.

When does Acaena bloom?

Acaena displays blooms of white from early to mid-summer, specifically noted as blooming from June to August.

Conclusion

Acaena inermis ‘Purpurea’ stands out as a resilient, low-maintenance option, delivering rich purple texture and excellent drought tolerance for sunny, dry spots. Integrating this unique Acaena into your landscape—especially rockeries or pathway edging—will provide year-round interest. Confirm local hardiness suitability now and plan for spring planting to maximize establishment this season.

Propagation Tips

Propagating this purple-leaved selection is incredibly easy, making it simple to increase ground cover coverage or share with friends. The primary method involves simple division of the established mats in early spring before new vigorous growth begins. Gently lift sections of the creeping stems, ensuring each division has healthy root stock attached.

Because the stems layer readily, you can also encourage rooting by lightly covering sections of the runners with a thin layer of sandy soil during the growing season. This semi-evergreen perennial establishes quickly when transplanted, provided the disturbed soil is kept barely moist immediately following division, contrasting its usual preference for dry soil.

Companion Planting

Due to its specific cultural needs—full sun and excellent drainage—companion plants for Acaena must share these preferences to thrive alongside it. Group Acaena inermis ‘Purpurea’ with other low-growing, drought-tolerant alpines and succulents. Excellent neighbors include creeping Thymes (Thymus spp.), low-mounding Sedums, and certain silvery Artemisia varieties that enjoy harsh, dry conditions.

Avoid combining this fast-spreading groundcover with delicate, moisture-loving plants in the border front. The aggressive nature of dense Acaena mats can easily smother smaller, slower-growing neighbors. Focus instead on robust plants that can handle occasional encroachment or those planted slightly further back where the Acaena’s spread is contained.