Acanthus Frequently asked questions

1. Why do the leaves on my Acanthus get white powder on them every year?

Answer
This is due to a mildew that is specific to Acanthus and is caused by lack of air movement around the plant and also by the density of foliage, impairing air movement. Either thin the foliage, move the plant to a more open situation, e.g. away from walls w here the air cannot circulate, or spray with a fungicide. Spraying is best done before the mildew is seen as; in this case, prevention is better than cure. Remove badly mildewed leaves and dispose of them to stop the spores spreading. Control with pesticides will become harder as the number of materials available is reduced. There is one commodity substance that can be used to control mildew; potassium bicarbonate (baking powder) at up to 10 grams per litre of water.

2. What is the best place to plant an Acanthus?

Answer
Acanthus like poor soils that are well drained. Too rich a soil will result in masses of foliage and few flower spikes. Full sun will produce plants that flower well but, if planted in the shade, Acanthus will grow perfectly well and will produce larger leaves and fewer flower spikes. This adaptability makes Acanthus a very useful plant for most gardens. A word of warning: once planted, Acanthus is very difficult to eradicate so do think carefully where you place them.

3. Why doesn’t my Acanthus flower?

Answer
This is probably due to there being snails in the crown of the plant. The flowers spikes are lovely and soft and extremely attractive to molluscs. Snails are often seen “sliming” along the leaves after it has rained. Another reason can be that the plant has been caught by a very sharp frost and the flower buds have been spoilt. The last cause could be exacerbated by the soil being too rich or if the plant is fed with too much nitrogen. In this instance, the plant is too well fed to need to flower or set seed.

4. I have only got a small garden but would like to grow Acanthus. Any suggestions?

Answer
There are many varieties of Acanthus and some of them are very suitable for small gardens; A.dioscorides being the most dwarf. There are many that can be kept contained by being grown in pots and, if fed and watered, they are very successful.

5. Can you grow Acanthus in pots?

Answer
Most definitely. (See answer above)

6. Are the tropical Acanthus hardy?

Answer
Acanthus sennii is completely hardy, dying right down in cold winters and often not starting back into growth until June. A.eminens will only tolerate a few degrees of frost. A. pubescens will tolerate short periods of up to 10 ?C. A.montanus will not tolerate any frost.

7. Are any Acanthus scented and are they attractive to wildlife?

Answer
Acanthus hungaricus is very sweetly scented and is a good plant for insects. A. spinosus and A. mollis are slightly scented, as is A. dioscorides. They are also attractive to insects.

8. How do you get rid of Acanthus?

Answer
A systemic weedkiller is the only sure way as digging out the plant will result in some broken roots and new plants will sprout from these, like dandelions.

9. How do you propagate Acanthus?

Answer
Root cuttings will reproduce an Acanthus plant exactly, as will division. Seed is easy to germinate but there is always a chance of seedling variation as the plants may cross-pollinate.

10.What do you do with Acanthus in winter?

Answer
Just leave the plants to get on with the winter weather. If leaves are frosted and look a mess, just cut them down and they will resprout as the weather warms up.

11. Are Acanthus harmful to pets?

Answer
Only if they get tiny thorns from th plants in their paws. Acanthus have been used as medicinal plants over the centuries and so are completely safe if eaten.

12.Are Acanthus good for flower arranging?

Answer
When dried, the flower spikes are useful for winter decoration. Just beware: when the seed pods dry out, the seeds are often shot out with some force! Unfortunately, it seems that the fresh stems and leaves do not take up water easily.

13. Are Acanthus evergreen?

Answer
There are some of the mollis varieties that will keep their foliage in the winter but, if the weather is really cold, then the foliage may die away completely.

Acanthaceae

Once we got hooked on Acanthus, it seemed obvious to look at the whole family of ACANTHACEAE. It is one of the largest and most widely distributed in the world: enter the word into Google and you will find sites with floras from Madagascar, Australia, Zimbabwe, Hawaii and Brazil to name but a few. Genera about 250.
Species about 2400.

Some of the plants are woody, scandent shrubs whilst others thrive in mangrove swamps. Many are perennials and most of those grown in the UK are herbaceous. There are also many climbers in this family, mostly from frost-free climates. They all have certain characteristics in common.

  • The leaves are opposite and are often naturally patterned.
  • The flowers are often clustered in pyramidal spikes and the petals are
    fused to form floral tubes, with the floral bracts often outshining and
    outlasting the flowers.
  • There is usually a swelling of the stem beneath the leaves.
  • Cuttings root internodally.
  • Seeds are often explosive on ripening.

When I have the time to write one, there will be a new section listing many of the Acanthaceae we have at the nursery.