With their big shaggy globes of trumpet-like flowers on sturdy stems often reaching well over 1m in height, Agapanthus makes a great impulse buy in high summer.

But customers can be assured that, although they look exotic, hardier deciduous varieties of these herbaceous perennials will survive overwintering well away from the south coast.

Although sometimes named lily of the Nile, these tuberous monocots are all endemic to South Africa, where their colours range from white to violet-blue.

With their tall, round umbels, they have been classed as a member in the Allium family, but they are also listed in their own monogeneric family.

They hybridise readily, and hundreds of varieties are now available, with breeding extending the range of colours and heights. They have been grown in Europe since the 17th century, and can even be seen growing wild in the Scilly Isles.

The so-called Headbourne Hybrids, bred in Hampshire in the 1940s and 1950s, and the many varieties derived from them, are deciduous and among the most hardy.

Agapanthus is naturally clump-forming, and ranges in height from 30cm dwarf forms such as 'Lilliput' to 2m giants such as 'Loch Hope', providing many different uses within the border.

Left uncut, the flower heads of the taller forms provide architectural interest into the winter, while the wreath of strap-like glossy basal leaves give colour and texture.

Being accustomed to the sandy slopes of the Cape, the genus thrives in full sun and dislikes heavy waterlogged soil, preferring slightly acidic conditions.

The plant will also benefit from monthly feeding, starting at spring time until flowering. Unusually, it grows as well, if not better, with its roots constrained in pots and containers.

This makes even the frost-tender varieties a viable option, as they can readily be brought into the glasshouse, conservatory or porch to over-winter. However, at this time they need to be monitored for red spider mites and mealy bugs; otherwise they are largely pest- and disease-free.

When left outdoors, crowns can be protected with a deep mulch of straw or bracken in frost-prone areas.

Roots can be divided in spring, which is the best way of ensuring consistency of cultivars. Species can be propagated from seed, flowering in their second or third year.

Selling this genus while in flower means customers have added confidence, given the variable nature of the plants.

What the specialists say

Sarah Wilks, owner, ProperPlants, Cornwall "The deciduous types are generally hardier and will grow virtually anywhere in the UK. They like well-drained soil and a sunny site and, once established, are very-drought tolerant plants. And the blues are really true blues, which is a rare colour in the plant world, and they always sell well.

"We concentrate on two- and three-litre pot sizes although larger options sell out quickly, showing the demand for an instant look in the garden. They look great in pots and actually perform better when roots are constricted.

"A good stock selection should be based on cultivar hardiness while providing a range of heights and colours, making sure there are one or two that are particularly suited to container growing. If you are being a purist about it, make sure plants are produced by division from known varieties, rather than from seed.

"Our customers' favourites include 'Navy Blue' - it just sells on sight. 'Buckingham Palace' is another blue cultivar popular for its towering height."

Richard Burt, sales manager, Wyevale East, Kent "Agapanthus is likely to remain a firm favourite for many years to come. There has been some great breeding work to advance the genus and its cultivars. "We sell such a large volume that it is almost becoming a speciality for us. The tall stems and sturdy flower heads require little staking, and add height and form to planting designs.

"There are new varieties arriving all the time, and we try to promote as many of them as we can. Right now the blue Headbourne hybrid is one most designers seem to go for.

"A new one for us is 'Dokter Brouwer', which, again, offers the popular blue flowers but with the added detail of a dark vein running through the petals. We offer them in pots from two to 10 litres. The larger sizes sell very well, and are better suited to surviving their first winter in the ground."

IN PRACTICE

Claire Smith, plant area manager, Sanders Garden World, Somerset "Agapanthus are great for summer sales. They put on a fantastic display of flowers all season long and make for a striking border plant.

"Blue and purple varieties have been really popular in recent years and that trend looks set to continue. Early in the season we retail these in two-litre pots, but as they come into flower we will have larger three- and five-litre specimens on show.

"Their show of flowers on tall stems is great for generating impulse sales and they fly out."

SPECIES AND CULTIVARS

A. africanus Award of Garden Merit (AGM) is a hardy, deciduous species that will grow to 80cm, with deep blue umbels in late summer.

A. 'Argenteus Vittatus' AGM is a variegated form, its 40-50 cm long grey-green leaves displaying white margins, with pale violet flowers on 60-90cm stems.

A. Back in Black, or 'B in B', has dark, almost black, stems combined with dark seed heads that add architectural effect after the deep-blue flowers have passed.

A. 'Black Pantha' is New Zealand-bred, and is one of the hardier evergreen forms, with deep-purple-blue flower heads in July and August.

A. 'Blue Giant' has large individual mid-blue flowers that give the head a fuller appearance, although it is one of the less hardy deciduous forms. It grows to 1m.

A. 'Bressingham Blue' is one of the hardiest varieties, and is successfully grown as far north as Aberdeen. Reaches 90cm.

A. campanulatus is a vigorous, deciduous species with light-blue bell-shaped flowers on stems up to 1m.

A. campanulatus var. albidus is a white form of the above.

A. caulescens AGM is a hardy deciduous species, with mid-blue flowers up to 1m.

A. 'Dokter Brouwer' has unusual dark-veined blue petals. Grows to 75cm.

A. 'Enigma' has pure white flowers with a blue base. This species is not hardy.

A. 'Flore Pleno' is a medium-sized form with powder-blue flowers. It grows to 50cm.

A. 'Gayle's Lilac' is compact and grows to 50cm with subtle lilac colouring.

A. Headbourne hybrids are available in a range of colours from deep blue to white, reaching a hight of 75cm.

A. inapertus, unlike other forms, features dark-blue to violet flowers that hang down.

A. 'Jack's Blue' is a very tall (1.2m) recent New Zealand-bred form, with large, dark-purple-blue flowers.

A. 'Lilliput', as the name suggests, is a dwarf form, to 40cm, with deep-blue flowers.

A. 'Loch Hope' AGM, at nearly 2m is one of the largest varieties and also among the latest to flower, in September.

A. 'Midnight Star' is a vigorous form with long flowers, which results in the plant having a larger flower head.

A. 'Peter Pan' is a dwarf species, its blue flower heads reaching only 30cm.

A. praecox, despite its name, which means "early", this 80cm-tall evergreen variety flowers dark-blue in late summer.

A. 'Purple Cloud' is another New Zealand-bred form, with rich-purple flowers.

A. 'Sky' is one of the most vivid blue varieties, its flowers have an unusual drooping habit. It is tall and grows to 1.4m.

A. 'Streamline' has loose, mid-blue flower heads on shortish stems that grow to 45cm.

A. 'Timaru' is a semi-evergreen form with deep-violet-blue flowers on stems reaching 80cm.

A. 'Tinkerbell' is a small variety which, unusually for the genus, has variegated foliage. Flowers only sparsely.

A. 'White Heaven' has up to 80 pure white flowers on 1m-high stems from August.

A. 'Windsor Grey' is a hardy form with grey-white flowers that fade to slightly pink.