Leeks are at their best now, onions are looking good in store, vegetable growers are planting overwintered onion sets and there is still time to plant ornamental onions. It’s a fine time indeed for members of the allium genus, whose grouping can best be described by the familiar pungency they release when crushed or cut.

Leeks have tested gardeners this summer by their need for frequent watering, but now, with the return of the rain, will grow slowly all winter. Even quite skinny ones will bulk up as April approaches.

After April, any unused ones will start to flower – this makes them useless for the kitchen, but their flowers are relished by pollinating insects. In fact, allium flowers are some of the best flowers for insects: each globular flower head contains numerous little florets rich in pollen and nectar.

Overwintered onion sets come close, in the South anyway, to being the perfect onions. They grow all winter and mature in early summer before drought strikes, leaving the ground free, if sufficient water is available, for another crop to mature from autumn, making good use of space in small gardens.
French beans or sprouting broccoli are good follow-on crops. Their downside is that they do not keep well, so only grow what you need from July to October.

Spring-planted onion sets produce sound bulbs from August that store for many months. Order now to plant from late February, bearing in mind that some – red onions and heat-treated ones – will flower prematurely if planted before April. The flat, pink “Pink Panther”, planted in March, makes an especially attractive and tasty onion that is seldom available in shops.

Garlic and shallots, also alliums, can also be planted now and are easy to grow. Shallot bulbs, small, sweet and mild, are surprisingly expensive in shops but simple to grow. Allow 45cm between rows and 30cm between plants.

Bulbous ornamental alliums are hugely popular, particularly those flowering in the in-between period after spring flowers and before summer flowers. Their dry seed heads remain attractive, and both flowers and seed heads look good in a vase, if you can bear to cut any.

It is getting late to plant allium bulbs, but plenty are still available to buy. They should do well enough in well-drained or sheltered gardens. Elsewhere, they can be pot-raised in a protected spot. Good ones include “Gladiator” (growing to 1-1.5m), with huge 20cm heads, bearing starry light purple flowers; “Purple Sensation” (1m), with 8cm deep purple heads; and Allium cristophii (60cm), violet, 20cm across and somewhat resembling a small explosion.

Edgier “Red Mohican” (above), 90cm, with a red mohican hairstyle flower, and “Forelock”, 80cm, maroon flowers with a tuft on top, bring a different floral drama to the border.

Herbaceous perennial alliums include the Egyptian, or walking, onion, which spreads by its bulblets, formed in place of flowers, rooting where the 1m stems fall. Usually consigned to the herb patch, it is becoming popular as a rather eccentric border plant and “edimental”.

Edimentals, as edible ornamental flowers are styled, are increasingly popular. The chive “Curly Mauve” is an ornamental curly leafed version of another herb garden favourite.

Allium “Bubble Bath” and the more compact “Lavender Bubbles” are perennials forming clumps, from which sprout spectacular massed, spherical, small flowers in lavender. If dead-headed, flowers form over long periods.

Allium “Millennium” stood up well to drought this year, bearing pink starry flowers from mid to late summer, which remain attractive even when mature and dry, and are valuable in sunny borders.

Guy Barter is the Royal Horticultural Society’s chief horticulturist. @GuyBarter

The RHS is a charity inspiring everyone to grow via its research, advisory, outreach, shows and gardens. For more information, visit: rhs.org.uk