Gardening: A canopy of stars

The seed heads and skeletons of alliums are just as dramatic as their glowing globes of flowers. Sarah Raven suggests which varieties to plant now for a dazzling display next year

ALLIUMS LOOK best at night, when few other things are visible. With their domes in full flower, they seem to glow in the moonlight. They are even more impressive when they've gone to seed, turning from green to pale straw. A collection of several varieties of differing heights, flowering at different times, will form a wonderful canopy of starry globes.

Some varieties are perfectly organised eruptions of ruler-straight stems, rather like chives, which are a variety of allium called A. schoenoprasum. Their flower heads look like sea-urchins thrust up into the air. Others have both pendulous and straight stems, attached to a central globe, and end in purple, mauve, yellow or white chive-like flowers.

The fresh flowers look great in a vase (try not to bruise the leaves or they will smell of onions), or you can harvest the seed heads to display through the winter, changing the water every two or three days. The skeleton plants also look good hanging upside down against a wall, especially against dark paint.

Alliums are good for the lazy gardener. Most are easy to grow, and they will reappear year after year. They thrive in full sun, in a well-drained soil, acid or alkaline, and, unlike many tulip and lily hybrids, they gradually multiply rather than dwindle.

If you garden on clay, or poorly drained soil, integrate shovelfuls of grit to make sure your crop doesn't rot. Plant them in September, so they have at least eight months in the ground to put down their roots before they have to produce a flower. You can pack bulbs in, planting the large ones about 4in deep, 16in to 20in apart to form a clump, the smaller ones need about half that distance.

The leaves appear in spring but most have died back, or are looking ragged, by the time the flowers erupt. Bear this in mind when you plant them, making sure they are planted in a combination that will cover up the foliage. You can cut off the leaves, but if you do this every year you will eventually starve the bulbs and they will disappear.

A. giganteum and hybrids like A. glaucum `Globemaster' have the most impressive flowers, each one the size of a small cantaloupe melon perched on a 3ft-high stem. It grows wild on gentle slopes at low altitudes in Iran, Afghanistan and central Asia. They make the perfect upper-storey plant, grown up through carpeting perennials like hardy geraniums or Viola cornuta to create a double layer of colour.

Allium schubertii make the best seed heads. They are huge, more like a water melon than a cantaloupe, with individual flower stems at least 6in long radiating out from a central point. A. cristophii has flower and seed heads which are slightly smaller, but its individual flowers are the largest of the lot. Each one is a six-pointed star in silvery-mauve, with a bright green centre.

Medium-sized A. hollandicum `Purple Sensation' is another lovely plant. It is one of the earlier varieties, flowering in mid-May, and has the richest, darkest purple flowers. The flowers are followed by green bead- like seeds, although they don't look so good when they are brown. They lack the skeletal fineness of A. schubertii and A. cristophii, but they are lovely when they're still bright and fresh. Use this one like lavender, planted in a broad stripe, three or four deep down the sides of a path, with bulbs scattered about 1ft apart. Through May, June and July the buds, flowers and then seed heads will lean in and over the path, forming a brilliantly-coloured aisle for you to walk through, the alliums a hovering presence on either side.

On a smaller, more compact scale, the smokey-purple A. sphaerocephalon is my favourite. This flowers later than most alliums; in bud in July, flowering through August, with gradually bleaching seed heads in September and October. Look out for A. cernuum `Major' with small, rich purple hanging flowers in chandeliers a couple of inches across. This self-seeds, but doesn't become a bore.

Some of them you do need to be careful with. They're pretty, but within two or three years of planting 10 bulbs, you will have 100 cropping up all through your borders and in every crack in your path. You think this is nice until you realise that the alliums are wiping out many of your more delicate plants. It's not the flowers that are the problem, but the lush green leaves which form a light-excluding carpet for anything trapped underneath.

The worst culprit is A. triquetrum. It has nice white flowers which look a bit like wild garlic, but it is dangerously invasive and you would be mad to introduce it into your garden. I love the weird pinkish-green and bronze bell-shaped flowers of Nectaroscordum siculum subsp. bulgaricum, which used to be classified with the alliums. It's now in a family of its own. It's not as overwhelming as A. triquetrum, but beware as this can be invasive too. It thrives in sun or shade and will gradually creep into every nook and cranny.

For a list of alliums send three second-class stamps to Rupert Bowlby, Gatton, Reigate, Surrey RH2 OTA or contact R V Roger Ltd, The Nurseries, Pickering, North York- shire YO18 7HG, tel 01751 472226, for a free catalogue

This week

Gardeners in the States have been enthusing about the benefits of coffee grounds in their compost. They are said to work particularly well on roses and mushrooms. Starbucks Coffee Company is offering its customers free grounds. For details of your nearest store, ring 0171 731 4599

August and September are the months for planting bearded iris. Ring the iris specialists: Croftway Nursery, Yapton Road, Barnham, Bognor Regis, West Sussex PO22 0BH, tel 01243 552121, or Claire Austin Hardy Plants, Bowling Green Lane, Albrighton, Wolverhapton, West Midlands WV7 3HB, tel 01902 373931. Put in your order to be sent out in the post now. Get them straight in the ground as soon as they arrive

Many penstemons are not reliably hardy in a harsh winter. Collect some cuttings now for over-wintering under cover to make sure you have plants for the garden next spring. This couldn't be easier to do. Collect some non-flowering side shoots, remove the bottom leaves and poke them into pots filled with a gritty mix of compost. Keep them in a light, warm place with moist soil and they will root in a couple of weeks