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One of the best things about working on the show this week is that we will be planting one of my favourite genus of flowering bulbs; the ornamental onion or Allium. What superb group they are, giving us such fantastic colour and form from May through to June. Who could imagine Chelsea week without the striking purple globes of Allium hollandicum 'Purple Sensation' or the fireworks of A. shubertii. Planting alliums in the Prairie border this week at Greenacre, however, required a more modest, almost shy species; Allium cernuum. While it is readily available, it is not as well known as others in its genus, but it is worth growing for its loose nodding umbels of pinky purple flowers. Its native to the North America and grows well in most soils and aspects, and will naturalise when it finds a spot it likes. With its relaxed manner, it will fit nicely into the prairie border, flowering into July. Toby will be planting it alongside Nectaroscordum siculum, which flowers slightly earlier. Closely related to Alliums, Nectaroscordum also have an open head of subtle creamy pink flowers that hang gracefully when open. Toby will be planting them in drifts, following the specific planting theme of the border, for some June interest.

For some spring colour and to provide some early Bee grub, Toby will be planting a succession of Alliums in the Bee Border also;

• A. 'Purple Sensation': appear in summer, showing off rounded heads full of deep violet flowers. These alliums are perfect for a sunny border. It is best to remove the immature seed-heads as the seedlings tend to have paler flowers. (AGM)
• A. schubertii: real stunner with round flower-heads measuring 30cm (1ft) wide, which resemble the starburst of a firework. The stems that pop out of the inner globe are thought to aid propagation by propelling the seed-heads.
• Allium cristophii: blockbuster with large purple heads measuring 20cm (8in) wide. These make superb cut flowers and have an almost metallic sheen on the stout stems, which reach knee height. Best placed in the spaces between border perennials to disguise its dying foliage. (AGM).
• A. sphaerocephalon: small, 2.5cm (1in) wide, pink to reddish-brown drumstick on long wiry stems. The flowers are densely packed and remain in bloom for many weeks.

Tonight's programme will also see Joe bringing back some mad colour combinations inspired by Trentham Gardens. Carol enthuses about the gorgeous Rudbeckias and Asters currently filling her Devon garden with colour. And we have a look at contestant number 3 in our Gardener of the year competition. We even have 2 seasonal culinary suggestions to add a little sweetness to your weekend!

Growing tips

Site and soil preferences

Alliums add impact to early summer borders and can be dried for winter decoration. They come in a wonderful range of colours including purple, buttercup yellow, pinks, white and shades of cornflower blue.

Alliums are extremely easy to grow, invariably needing a place in full sun right at the front of a border.

In the wild, alliums often grow in poor, stony ground and they don't need pampering in the garden. Average soil is fine, but it must be free-draining.

Alliums in pots

Even gardeners with tiny gardens can grow alliums in containers. Always use a reasonably deep container, especially for larger varieties. Plant at three times the depth of the bulb in well-drained compost (this also applies when planting in the open ground).
The container plants will need repotting into fresh compost every year, but you don't need to do any more than this. They shouldn't require extra feeding, either, as long as their foliage is left to die back naturally. This enables them to build up energy for the following year. Like some other bulbs, they're naturally long-lived and survive for years if left undisturbed.

With large drumstick alliums, the dying foliage can be disguised behind a few pots of bushy annuals or a clipped box for a more formal look.