Onions are obviously edible, but they also produce highly decorative flowers and, if you’ve ever let a leek or an onion go to seed, you’ll know all about this family’s sculptural charms. Some varieties are specifically grown for their flowers. But they are a diverse bunch and they vary between the foot-high, yellow firework Allium flavum to the beefy, almost a metre high ‘Gladiator’.

Like all bulbous plants they prefer good drainage, rather than wet soil, and as a general rule the silver-purple varieties like hotter and warmer conditions than the deeper-toned purples.

The star performer for me is the May-flowering ‘Purple Sensation’, a hardy, easily grown and long-lived allium that’s widely available. ‘Purple Sensation’ follows straight after the latest tulips, producing a domed head of tactile, deep-purple flowers. But you do need other plants as well, because the foliage tends to wither badly as the flowers appear. Let it pop up through the silver-leaved, lemon anthemis ‘Susanna Mitchell’ or use filigree artemisias like ‘Powis Castle’.

‘Purple Rain’ (pictured above) is a newish variety displayed at this year’s Malvern Show by the Dutch bulb firm Warmenhoven. It may be difficult to find, but Jacques Amand are selling it (tel 020 8420 7110).

Other May and June flowering varieties for ordinary garden conditions include ‘Gladiator’. This produces large rose-purple balls on stems that can reach over 150 cm. ‘Globemaster’ is only half the height. But the starry, pale-lilac flower heads can measure 20 cm in width, hence the name, and the substantial leaves are green and glossy. Individual bulbs of both varieties are expensive and may cost £5 each.

Allium giganteum is the tallest of all, reputedly reaching 170 cm (over 5ft ), and the round flowers are pinker in tone. But I haven’t grown this one – yet.

The silver-lilac, June-flowering alliums are shorter in stature, but their flowers are even more sculptural so they need space to shine. They also need a warm position if they are to shimmer and shine – and overwinter A. cristophii produces a spherical head of well-spaced radiating stems, each topped by slender-tined lilac stars. But A schubertii is even more fascinating: it puts out stems of different lengths and, once the head has dried, it looks very sputnik-like. Both are adored by flower arrangers, but all alliums cut well.

July-flowering varieties include the drumstick allium (A sphaerocephalon) and the ragged-topped ‘Hair’. The drumstick allium is variable in form, but good examples have two-toned green and maroon flowers. These blend amazingly well with the pony tail grass Stipa tenuissima.

‘Hair’, an Afro-style allium, is rather like a ragged crow garlic and it scatters little bulbils in August. Both need to be planted in swathes to create an effect.

Athough alliums need planting between September and November, they do most of their growing before and during their flowering season. The taller ones add strong vertical lines – something every garden needs.