Biennial grown as annual for swollen bulbs. Value: small amounts of most vitamins and minerals.
A vegetable of antiquity, onions were cultivated by the Egyptians not only as food, but also to place in the thorax, pelvis or near the eyes during mummification. Pliny recorded six varieties in Ancient Rome. The onion was highly regarded for its antiseptic properties, but many other legends became attached to it. In parts of Ireland it was said to cure baldness: ‘Rub the sap mixed with honey into a bald patch, keep on rubbing until the spot gets red. This concoction if properly applied would grow hair on a duck’s egg.’ Bulb onions are classified as early, mid-season and late-season types and it’s very important to choose the right variety for the location and time of year.
Varieties of fall into different groups according to colour, shape and use. The bulb or common onion has brown, yellow or red skin and is round, elongated or spindle-shaped, or flattened. Green or bunching onions are harvested small, as are pickling varieties (also known as ‘silverskin’, ‘mini’ or ‘button’ onions).
Bulb or Common Onions
Bulb varieties are classified by their colour, shape and strength of flavour as well as their seasonal classification. Early, mid- and late season correspond with short, intermediate and long day varieties and are classified by the period of daylight needed for bulb production.
The old English variety, ‘Alisa Craig’, is grown in cool areas for exhibition purposes. ‘Albion’ is a round white bulb and ideal in salads or stir-fries. ‘Barletta’ is the earliest onion, with flat, white bulbs that mature when day lengths reach 12–13 hours. It can be lifted at pickling size (70 days) or left to mature. Late-maturing ‘Brown Spanish’ is a medium-sized, globe-shaped onion with good keeping quality. ‘Creamgold’, also known as ‘Pukekhoe’, is large, light brown, globe-shaped with creamy-white, spicy-flavoured flesh. It is suitable for cool climates and is the best keeping onion. ‘Early Flat White’ is best used in early spring while still green. ‘Gladalan Brown’ is mild and early maturing and a heavy yielder, suited to warmer climates. ‘Hunter River Brown’ and ‘Hunter River White’ are globe-shaped early onions. ‘Lockyer Early White’ is suited to warm climates. ‘Long Red Florence’ is spindle-shaped, sweet and mild-flavoured. Mid-season ‘Odourless’ is a large flat brown onion with mild cream flesh. ‘White Globe’ is commonly available as seedlings. Variously named Spanish red onions are available including ‘Early Californian Red’, ‘Sweet Red’ for mid-season and ‘Red Brunswick’, a late-maturing, good keeper. ‘Red Italian Torpedo’ is a mild-flavoured intermediate day length variety with red skin and distinctive elongated bulbs. It is good for salads but does not store well.
Green, Spring or Salad Onions
Confusion reigns because of inconsistency in naming between seed packs, greengrocers, food and gardening writers who variously call these plants scallions (their American name), bunching, spring, salad and green onions, and, erroneously, shallots. A spring onion is really an immature onion that has not yet made a bulb and is harvested for its green shoots. Japanese or Welsh bunching onions, , form a thickened leaf base and are perennial in most climates. They can be grown in warmer climates than bulb onions. Potato onions and Egyptian or tree onions, that produce small bulblets atop seed stalks, can be purchased from specialist suppliers. ‘Ishikura’, a cross between a leek and coarse chives, can be left in the ground to thicken and still retain its taste. Japanese-bred ‘Straightleaf’ stands clear of the soil with an upright stature. ‘White Lisbon’ is tasty and reliable, with a small white bulbous end. It is fast growing and very hardy. Mail-order catalogues offer some interesting red-stalked varieties.
Pickling onions tolerate poorer soil than other types. ‘Borettana Yellow’ is a sweet pickling onion that is also suited to salads. ‘Paris Silverskin’ is a rapid grower. ‘Pearl Pickler’ is a white early.
Onions require an open, sunny site, fertile soil and free drainage. Onions are mostly grown as a winter crop in home gardens and are best in cool climates. Bulb types are difficult to grow in subtropical climates and unsuitable for tropical zones. Choosing a variety with the correct day length requirement and sowing the seed at the right time of the year is vital for successful onion growing. Incorrect choice may mean onions will not form bulbs or bolt prematurely. Gardeners in southern zones with over 15 hours of daylight in summer can grow any variety. In warm temperate latitudes, grow short and intermediate day-length varieties. Late varieties form bulbs when day lengths reach 15 hours so are not suitable for northern latitudes.
Southern gardeners can extend their harvest season by growing one variety of each day length but should sow early, mid- and late varieties in that order from April through to early spring. In warm temperate zones, sow early onions from March–May and mid-season varieties from June–July. Subtropical gardeners are limited to planting early cultivars from mid-autumn to winter.
For a constant supply, 2–3 plantings are needed, one in spring and another in summer when Japanese varieties are planted, or autumn when old hardy types are used. Bulb onions can be planted from seed, seedlings or sets. Seed provides a greater choice of varieties. Seed can be sown into trays, punnets or beds and transplanted, but direct sowing is easiest.
Sow seed 1–2 cm deep into compost-enriched, damp soil in rows 25–30 cm apart. Seed will take 10–14 days to germinate, or longer in colder weather (below 10°C). Thin seedlings to 2—3 cm apart and later to 7–10 cm apart, depending on variety size, leaving sufficient room for the bulb to develop. Second thinnings can be used as green or salad onions.
For transplants, trim tops of seedlings to about 2.5 cm and trim roots. Avoid planting them too deeply. Ensure that the roots fall down into the planting hole and that the base of the bulb is just below the soil surface.
Onion sets are immature bulbs that mature 4–5 months quicker than seed. They are good for cooler areas with shorter growing seasons and grow well in poorer soils. Plant onion sets in mid to late October (timing is important). Plant in shallow drills or push them gently into the soil until only the tips are above the surface. Space them 10–15 cm apart in the rows.
Sow spring or bunching onions thinly in rows 10cm apart. Thin if necessary when the seedlings are large enough to handle. Water the drills before sowing in dry weather. Grow as a winter crop in subtropical and tropical zones. In temperate zones, sow at 2–3 week intervals throughout the year for a regular supply. Sow in spring in cold zones. Japanese and Welsh bunching onions can be divided and replanted in spring or autumn.
Sow pickling onions at the time of year indicated on the pack, either broadcast or about 1 cm apart. Thin according to the size of onions required and harvest them when the leaves have died back.
Dig bed, incorporating a general fertiliser or well-rotted manure or compost well before planting time. Do not add fresh manure or blood and bone close to sowing time. Avoid excess nitrogen, which will result in top growth at the expense of the bulbs. Lime acid soils. Before planting, rake the surface level, and walk over the plot to create a firm seedbed.
Bulb onions have a long growing period, so may need a light side dressing of complete fertiliser or a liquid feed when bulbs start to form. Keep beds weed-free, particularly in the early stages of growth, as onions have a shallow root system and suffer from competition with weeds. Hand weed around plants, shallow cultivate between rows and mulch to reduce water loss and weeds. Maintain moisture but avoid over watering. Plants will push themselves up in the surface of the soil as they grow. Bulb onions should sit on the surface of the soil, not below it.
Harvesting and Storing
Bulb onions take 6–8 months to mature from seed. They are mature when the foliage topples over naturally and the leaves begin to dry out. Do not bend the leaves over. Lift when the dried foliage rustles. Cure bulbs in the sun for a few days. In bad weather, spread out the bulbs in trays indoors, and turn them regularly. Handle carefully to avoid damage and disease. Remove damaged, soft, spotted or thick-necked onions before storing. Store in a cool, dry place in trays, net bags or tights, or as onion ropes. Onions are hard to store in warm and humid climates, where they are prone to rotting, rooting and sprouting. Long day length varieties store better than early, short-day onions, and brown onions store better than white onions.
Harvest salad or bunching onions before the bases swell. During dry weather, water before harvesting to make pulling easier.
Making an Onion Rope
Storing onions on a rope enables the air to circulate, reducing the possibility of diseases. You can plait the stems to form a rope, as with garlic, but they are usually too short and are better tied to raffia or strong string. Firmly tie in 2 onions at the base, then wind the leaves of each onion firmly round the string, with each bulb just resting on the onions below. When you reach the top of the string, tie a firm knot around the bulbs at the top, then hang them up to dry.
Pests and Diseases
Onion thrips congregate at the base of the central leaves especially in dry weather causing white flecks on foliage. Small plants may be killed. Well-watered larger plants will survive unless infestation is very severe. Keep plants well watered. Inspect throats regularly. Spray with a suitable pesticide if necessary.
Onion maggot causes problems most commonly in sandy soil and when animal manure or blood and bone is added near planting time. Use inorganic fertilisers where this has been a problem. Spray with a suitable insecticide just after seedlings emerge and repeat 10 days later. Fungal diseases are the main problem with onions. Control by crop rotation and adding lime to the soil prior to planting.
Downy mildew is common especially in damp conditions and severe infestations can kill plants. Improve soil drainage and air circulation. Control with copper-based sprays, applied regularly during rainy weather. White rot appears round the base of plants as white mould like cotton wool, dotted with tiny, black spots. Leaves turn yellow and die. It is almost impossible to eradicate. Remove affected onions with as much of the soil round them as possible, dispose of plants and any debris – do not put on the compost heap. Avoid spreading contaminated soil on tools or boots. Don’t plant members of the onion family on the existing site indefinitely. Neck rot occurs in storage. Let onion tops mature and dry thoroughly before harvesting. Don’t cut them off too close to the bulb. Only store undamaged bulbs. Store them in a cool, dry well-ventilated situation.
Tip: Blanch bunching onions by hilling around the stem.
Bulb onions can be grown in containers, but yields will be small and not really worth the trouble.
Used as an antiseptic and diuretic, the juice is good for coughs and colds. The bulbs and stems were formerly applied as poultices to carbuncles.
So indispensable are onions for flavouring sauces, stocks, stews and casseroles that there is hardly a recipe that does not start with some variant of ‘fry (or sauté or sweat) the onion in the oil or fat until soft…’ They also make a delicious vegetable or garnish in their own right: roasted or boiled whole, cut into rings, battered and deep-fried, or sliced and slowly softened into a meltingly sweet ‘marmalade’. Finely chopped raw onion adds zing to dishes like rice salad; you can also use the thinnings to flavour salads.
Bunching onions are perfect for salads, pastas, soups and flans. In France they are chopped, sautéed in butter and added to chicken consommé with vermicelli.
Pickled onions are an excellent accompaniment to bread, strong cheese and pickled beetroot — the traditional Ploughman’s Lunch. Besides being pickled, pickling varieties can be used fresh in salads and stir-fries, added to stews or else threaded on to kebab skewers for barbecuing.