Acanthus mollis: For foliage and flowers, sun and shade

Acanthus mollis foliage

Acanthus mollis is also known as the Oyster Plant or Bear’s Breeches. It is a plant I very often incorporate into my gardens.

It is easy to grow, creates a good shape in the border and provides interest through both its foliage and its flowers.

Acanthus mollis plant notes

Family

Acanthaceae

Plant Type

Herbaceous perennial

Soil Type

Prefers moist, well drained soil

read more on soil type here →

Aspect

Can be planted in sun, shade or partial shade

Eventual Size

Will grow up to 1.8m high and spread to 1.5m wide.

Hardiness

Hardy down to at least -20 celsius (-4 degrees F), so hardy in most areas.

read more on plant hardiness here

Uses and growing conditions

Acanthus mollis is a clump forming, evergreen soft-wooded perennial with an architectural habit. It grows up to 1.8m (6 feet) high x and can spread to as much as 1.5m (4 feet) wide.

It has multiple large (up to 1m in length) glossy, dark green lobed leaves and it its height comes from tall spike of purple, green and white flowers with spiny bracts. These make great cut flowers.

Use it as a robust, lush ground cover in shade or as a feature plant in mixed borders. with perennials like Thalictrums or Dahlias. Its dark and glossy foliage provides a foil for many flowering plants. Given its size and height it can work towards the middle or back of the border, but if planted at the front of the border, the beautiful leaves will be more visible and will nicely offset the plants growing in front of it.

Interestingly, the striking leaves of this plant are the ones used as on the friezes and columns of classical Greek architecture.

If you plant Acanthus in full sun, it will encourage flowering but where heat is intense, it is likely to produce leaf scorch.

Acanthus mollis flower
Acanthus mollis flower

Therefore, it is better to grow Acanthus mollis in full to partial shade in hot climates.

In more temperate climates it can be grown in full sun or partial shade.

It will grow in any fertile, well drained soil but prefers a deep loam. It is frost hardy to -15to -20 degrees C and is moderately drought tolerant when established.

Maintenance

Pruning is only necessary to remove spent flowers and old leaves.

Water well to establish and mulch well to maintain moisture in the soil. Apply a general purpose fertiliser twice a year.

Be aware that it can be a bit ‘weedy’ because, once established, Acanthus mollis is very hard to remove.

It roots deeply and if you dig it up, you will almost certainly find that it re-grows from scraps of roots that are left behind.

Pests and diseases

Can suffer the attentions of slugs and snails and also be troubled by powdery mildew.

Propagation

You can propagate by seed (warmth is need for germination), by division of clumps in spring or autumn or by taking root cuttings in winter.

FAQs

Does Acanthus mollis like shade?

This is a question that is often asked, probably because Acanthus mollis is one of those rare plants that can do well in shade or full sun.

In sun it will flower more and its leaves will not be as large. In shade, the opposite happens – there are less flowers and the leaves tend to be larger. This is because in shade more leaf surface area is required to enable the plant to photosynthesise enough light to let in grow well.

Does acanthus grow in full sun?

Yes, Acanthus will grow well in full sun in most climates. In very hot climates, Acanthus will survive in full sun, mainly because it roots deeply, but there is every chance that its leaves will scorch.

Is Acanthus mollis invasive?

As indicated above, Acanthus mollis is a hard plant to remove once it is established. If you dig it up, it will regenerate from any pieces root left behind – in fact it is this capacity that means you can easily propagate the plant form root cuttings. However, it doesn’t usually seed around much in temperate or cooler climates.

Is Acanthus an evergreen?

Yes, the leaves remain all year round.

Do you cut back Acanthus?

Cut back the finished flowers spikes, although you can leave them over winter as they provide a point of interest. The leaves are evergreen, but it is a good idea to cut back older scruffier foliage for a neater look.

Does Acanthus flower every year?

A healthy Acanthus plant will flower every year, although it will produce less flowers in shade or if it becomes very congested.

What is the difference between Acanthus mollis and Acanthus spinosus?

Acanthus mollis and Acanthus spinosus are similar looking plants, with similar looking flower spires. The main difference is that the leaves of Spinisosus are smaller, with more finely cut lobes. They also end in a sharp spike.

References

  • Brickell, C. (2016). Royal Horticultural Society AZ encyclopedia of garden plants. Dorling Kindersley. London.
  • Rice G (ed), 2006, the Royal Horticultural Society Encyclopedia of Perennials, Dorling Kindersley, London.
  • Rowell R, 1991, Ornamental Flowering Plants in Australia, University of New South Wales Press, NSW.
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