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Best uses

A stunning addition to garden beds and borders. Often used as a bold accent or specimen plant. If mature seed heads are left on the plant, it provides winter food for birds. Can also be used for dried flowers.

Physical characteristics

Large, deciduous perennial with upright growth of up to 1.5m when in flower.

Flowers and foliage

A large, clump-forming perennial with silvery-grey leaves up to 50cm in length. Thistle-like purple flowers are produced through summer and into autumn.

Preferred site

Grow in fertile, well-drained soil in full sun. Shelter from strong winds.

Preparation for planting

Generally, these plants require dry, sunny situations with very good drainage in winter. In the shade, silver foliage plants stay a dirty green colour. Avoid heavy, excessively wet soils and overcrowded positions. Ensure good air movement to keep foliage dry; overhead irrigation. Before planting, improve drainage by incorporating coarse gravel (e.g. GAP 40) into the planting hole. Always choose healthy, well-grown plants and plant after autumn rains. Before planting, ensure the root ball is saturated and remove the planter pot with minimal root disturbance. Trim any broken roots and plant at the same level as in the container. Dig a hole twice the diameter of the root ball, press in and water once planted. Make sure plants are watered well until established if planting in a drier period. Plant with some general slow-release fertiliser, and then every spring apply organic fertiliser (e.g. blood and bone) at a handful per square metre.

Cardoon can be grown from seed starting in mid-winter to late spring. Sow seed in individual 7cm pots and place under glass or in a cold frame (without heat) six to eight weeks before planting in the garden. Plants grow slowly at first and should be transplanted into a larger container for sizing up before transplanting into the garden. Cardoon requires well-drained, fertile soil and full sun to prosper. They grow fast in the garden once the warmth of summer begins.

Plants will establish slowly and seem to not grow for the first few weeks after transplanting. Water abundantly to keep the leaf ribs tender. The plants may require copious amounts of water during the summer. The thistle heads can be cut and used for displays, or can be removed when colour fades.

Maintenance tips

In very cold winters apply a dry mulch plants with silver foliage appreciate a mulch of gravel to keep their stems and leaves off the wet ground in winter. These perennials require very little in the way of grooming other than the tidying of old and damaged leaves throughout the growing season. The ideal time to cut back this group of plants is in early spring. Unless the soil is very poor no fertiliser is required. An annual application of lime to acidic soils would be beneficial as cardoon are found naturally on limestone formations. Make sure there is plenty of room for growth so as not be crowded by neighbouring plants.

Ecological and biodiversity benefits

Large blue-violet or purple blooms which are highly attractive to bees and other pollinating insects. If the seed heads are allowed to mature, small seed-feeding birds such as finches will feed over winter.

Pests and diseases

Can be damaged by slugs, snails and blackfly.

Location at Auckland Botanic Gardens

Edible Garden

Interesting facts and tips

A close relative of the globe artichoke, gardeners often grow cardoons for their appearance and culinary uses. It is difficult, if not impossible, to find them at a supermarkets. In France, Italy, Spain and other European countries where the cardoon still thrives, you are likely to find many different dishes.