They give height to flower borders and are blooming marvellous at this time of year. KATIE EDWARDS looks at the allure of alliums.

ALLIUMS, originally only grown in the vegetable garden, are now very popular in garden beds and borders for their striking colours and architectural impact.

Bright purple bulbous flowers sit at the top of green stems that can range from 3 to 6ft tall. Summer is prime flowering time for alliums and the current warm spell is working in their favour.

Alliums are practical, decorative and spread colour throughout the garden. The ornamental flower heads come from a variety of plants belonging to the onion family; for example, shallots, leeks, garlic, and onions and essential herbs such as chives. There are over700 different types of alliums in the world but the most popular ones are known as Purple Sensation, Globemaster and Gladiator, Corkscrew and Ozawa Allium.

The Royal Horticultural Society (RHS) advise that alliums must be planted in early autumn and sheltered in well-drained sunny areas. Fertile soil is preferred but grit should be added to improve the drainage system.

Freshly manure is unsuitable soil for these plants. Be sure to plant allium’s behind the foliage of other plants, in borders or deep pots, so that the bulbs are not completely sheltered from sunlight. Cold and waterlogged areas are poor conditions for planting alliums.

Ben Mayo, 24, Chepstow Garden Centre’s shop floor manager, advised: “Be careful not to saturate the soil and just keep it moist. Alliums like some shade and not too much sunshine.”

The best way to propagate alliums is to plant the bulbs at a depth four times the diameter of the bulb. (RHS) suggest that small bulbs should be 3-4 inches apart but taller ones up to 8 inches apart. Sometimes alliums create offsets – small clusters of offspring from the bulbs in the ground.

This is noticeable above the ground when leaves wilt and flowers pass their peak and die. If this occurs, make sure that the flowering stage has come to an end and carefully lift and detach the bulbs from the earth.

]To restore the allium’s offsets, re-plant the bulbs in gritty compost and allow them to grow further. (RHS) recommend an alternative propagation method to store seeds in ‘a fridge and sow in spring at about 13°c and most will germinate within 12 weeks’.

As with all plants, alliums are susceptible to ‘the same pest and diseases as culinary onions ’: onion white rot, downy mildew and onion fly. Problems are easily avoided if they are planted along the edge of the border. Alliums are generally pest free and there is little need for pruning.