Gardens: Know your onions

The last of this season's alliums, A. angulosum, is still flowering in the garden. The first, A. paradoxum, started in March. That's a good spread to get from just one family of bulbs, especially as we tend to think of all alliums as late-May to June flowers, blobs on sticks, most of them purple. Over the past year, I've grown about 30 kinds, yellow, blue, white, pink as well as purple and though the monsters may be the most eye-catching, the miniatures have been the most interesting. Alliums are found wild all over the northern hemisphere, in the Alps, the Mediterranean and the Pyrenees as well as the Middle East, western China and North America. Most are tough and completely hardy, though a few such as A. schubertii, with its mad, explosive flower, are best treated as frost hardy. This one doesn't like winter temperatures to dip lower than -5C. Most alliums need open ground, and do best in well-drained soil in full sun, but again there are exceptions: the little mouse garlic, A. angulosum grows in shade. So does A. moly 'Jeannine'.

Planting depth depends on the size of the bulb. The bigger they are, the deeper they should go, but if you plan to grow alliums among herbaceous plants, it is a distinct advantage to plant deeper than the norm, at least 12-15cms down. You will then be less likely to spear the bulbs on your fork during an autumn clean-up, when you may well have forgotten where you put them. Alliums, such as A. senescens that grow from rhizomes rather than bulbs, need shallow planting, just under the surface of the soil. Heavy soil can be improved with coarse sand or grit, mixed in the planting hole. Add a handful of bonemeal as a long-lasting fertiliser. However hideous it looks, do not be tempted to cut back the foliage. Allow it to die down naturally; it feeds goodness back into the bulbs for the next season.

The good news is that neither deer, rabbits nor squirrels seem to fancy alliums. And mice, always demons where bulbs are concerned, will go for crocus and tulips before they turn to anything else. But being members of the onion tribe, alliums may suffer from common onion problems such as white rot, downy mildew and onion fly. Your best defence against disease is to get the growing conditions right. Remind yourself where alliums grow in the wild (often a mountainous area where the ground drains like a sieve) and try to give them the same conditions in the garden. This usually, but not always, includes a dry rest after flowering.

Bulbs should be planted this month or next so if you want to experiment with alliums that you've not grown before, where should you start? That depends on the conditions you can offer, the style of the garden and the season you want to fill. Pure white Allium paradoxum var. normale, the first into bloom, is a quiet beauty, with the added bonus of doing well in shade and on heavy clay soils. The wild species, native to Iran and the Caucasus, rarely produces more than a head of green bulbils, but this form, about 25cm tall, was introduced from northern Iraq in 1966 by the fine plantsman-artist, Paul Furse, and is a different thing altogether. It has nodding heads of gleaming white, bell-shaped flowers at the top of a bright green stem, as clean and crisp as a spring leucojum. Unusually for an allium, the leaves stay fresh while the flower blooms. It's not made for a border, but for a shady, tucked-away corner of a garden, where, having forgotten about it during summer when it disappears underground, you can be surprised by it in spring. Set the bulbs 8-10cm deep and the same distance apart.

This summer, I've been particularly grateful to the alliums that bounced into action in July and August, when the garden needed that kind of boost. One of them, A. tuberosum, or Chinese chives, I grew in our old garden, where it divided up the herb garden into a series of diamonds each filled with a different plant. Like ordinary chives (A. schoenoprasum) it clumps up quickly, producing clusters of starry flowers which come out in turn. Open, they are pure white, though in bud they seem tinged with pink because of the thin but very distinct pink line drawn up the midrib of the three tiny outer petals of each star. The flowerheads are small but they come at a good time of year (July-September) and, 65cm or so tall, are held well above the flat leaves. Home for this allium is eastern Asia, where it is widely cultivated for cooking, but it seems to be as happy in temperate as in tropical climates. It's a decorative addition to a veg garden or you can plant it among dwarf agapanthus for a Chinese willow-pattern effect. The bulbs are best bought damp-packed, as they are still in leaf in autumn when bulb nurseries send them out. Plant the little clumps in full sun, setting them about 5cm deep and 10cm apart.

The foliage of these late alliums, A. tuberosum and A. angulosum is much better behaved than that of the big purple drum-mallet alliums. That dies noisily just as the flowers are coming to their peak whereas the leaves of A. tuberosum stay bright and fresh. A. angulosum is even better because the leaves, narrow and flattened, are a brighter, glossier, more sparkling green, an excellent foil for the flowers. In the wild this mouse garlic, as it's called, likes damp grassland and it would be worth trying to naturalise it, if you've got grass that's not too coarse and bossy. The head is a half-sphere of lilac, no more than 5-6cm wide, similar to chives, though bigger and paler. It's an easy plant, interestingly slow to develop, so you're not going to miss it if you go away on holiday. It's a quiet plant, with a pleasantly wild feel about it. The bulbs are best bought damp-packed as they are still in leaf in autumn. Plant the little clumps 6-8cm deep and about 22cm apart. They increase rapidly.

Of all the smaller alliums I've grown this year, my favourite, I think, is Allium flavum, which started to do its stuff in late July. Southern Europe is its home and dryish hillsides its preferred habitat. That tells you what it needs in a garden: not the dampish heavy ground that suits A. angulosum, but a hot, dry place, perhaps a gravelled area, certainly well-drained. It's a variable species, particularly in terms of height, but the form I grew was about 30cm tall, with glaucous leaves. The flowering stems are thin and wiry, developing at the top into a long, strange, wispy spathe that breaks open to release a crowded mass of flowers. There may be 30 in a head, clear lemony yellow and held on little stalks unequal in length. The outer flowers open first and hang down, while the buds of the inner ones stand up. Meanwhile, the wispy tails of the spathe curve out and down in an elegant parabola. In silhouette, it looks superb. Though a sun-lover, it does not like to dry out completely and so is best bought damp-packed. Plant the bulbs 8-10cm deep and about 10cm apart. Try it on a gravel scree, between low growing mounds of a variegated thyme, with thrift or among grey-foliaged pinks.

'A. angulosum' and 'A. tuberosum' are available from Avon Bulbs, Burnt House Farm, Mid Lambrook, South Petherton, Somerset TA13 5HE. Tel: 01460 242177, website: avonbulbs.co.uk. Send 4 x 2nd class stamps for catalogue. 'A. paradoxum var. normale' and 'A. flavum' (including the form I grew which was the subspecies 'tauricum') are available from Choice Landscapes, Priory Farm, 101 Salts Road, West Walton, Wisbech, Cambs PE14 7EF. Tel: 01945 585051, website: choicelandscapes.org. Send 6 x 1st class stamps for a catalogue

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