Foundation of a great dish Onions are an essential, tasty part of our cuisine. They're members of the large Allium genus, which also includes garlic, leeks and chives, as well as the many ornamental alliums in perennial gardens.There are three edible groups. The familiar bulb onion (A. cepa) is in the Cepa Group. Picked young, when it has a small, white bulb and green tops, it's known as a scallion, or a green or spring onion. Left to mature, it's used in cooking or salads. Shallots produce multiple bulbs from a single planted bulb and belong to the Aggregatum Group. Welsh, or bunching, onions belong to a different species altogether—A. fistulosum.Bulb onions can be grown from seed or sets, which are small bulbs harvested the previous summer and stored over the winter. Although sets are easy to plant and give a quick start, the resulting onions are more prone to disease and bolting, and don't store as well as those grown from seed. Also, there's a wider selection of varieties available from seed.In Canada, Spanish-type onions should be started indoors in February; any later and the bulbs will be small and too strong-tasting. Onions you plan to store over the winter can be seeded directly outside at the same time as peas, but in most parts of Canada, a better crop will result from starting seeds indoors at the beginning of April.Plant them in either flats or cell packs filled with seed-starting mixture. In flats, sow five millimetres deep, five millimetres apart in rows five centimetres apart. For cell packs, plant three seeds per cell. Maintain a temperature of 18 to 21°C. Once they germinate (seven to 10 days), place seedlings under a grow light or in a sunny, south-facing window and keep at a cool temperature (around 15°C). Keep plants well watered (water-stressed plants produce small, strong-tasting bulbs) and feed with a half-strength organic fertilizer every two weeks. When the seedlings are 2.5 centimetres high, thin to one centimetre apart in flats or one seedling per cell. Trim tops to 10 centimetres. When danger of heavy frost has passed, harden them off by gradually exposing them to cooler temperatures and direct sunlight.Plant seedlings in fertile, well-drained soil in full sun. Prepare the area by removing weeds and digging in lots of compost or composted manure, adding extra compost and coarse sand to heavy clay soil. If the area has poor drainage, grow the onions in raised beds.Dig individual holes or a long trench about five centimetres deep. For seedlings grown in flats, use a knife to remove them, then gently separate individual plants. Spread out the roots and firm the soil around its base. For seedlings grown in cell packs, keep the soil ball intact. Plant 10 to 15 centimetres apart, depending on the mature size of the variety.Buy firm, disease-free sets that have no sprouts. Avoid larger bulbs, as they'll go to seed. Plant with the tips just below the surface, with the flat ends down. Once a month, side-dress with compost or organic fertilizer. Harvesting ideas and pests to watch for Onions form bulbs in response to the number of daylight hours. In Canada, grow the long-day varieties because short-day onions produce smaller bulbs.Unfortunately, Canadians can't grow very mild, sweet Spanish onions, such as the popular ‘Vidalia', but ‘Walla Walla', ‘Super Star', ‘Ailsa Craig', ‘Riverside Sweet Spanish' and ‘Candy' are mild, sweet varieties that grow well here. Red-skinned ‘Red Burgermaster' has red-and-white flesh. None of the Spanish onions are suitable for long-term storage. (They'll keep for about one month; cooking onions will keep for four to seven months under ideal conditions.)Not all regular cooking onions store well over the winter either. ‘Copra', with its firm flesh, stores longer than any other variety. ‘Frontier' is an earlier onion that stores nearly as long. ‘Redwing' is the longest storing of the reds.‘Crystal Wax' and ‘Barletta' have silvery white skin, small, round bulbs and mild, crisp flesh that make them ideal for pickling. ‘Pacific' is a scallion that can be left in the ground to form small bulbs that are also suitable for pickling.Harvesting and StorageToward the end of summer, when about half the tops have fallen over and bulbs are forming a papery skin, gently knock over the tops by hand or with a hoe, bending but not breaking them. Pull out any that have flower stalks and eat them first, as they won't store well. Leave the rest in the ground, without watering, until the tops begin to wither. Then dig them up, gently brushing off the soil (don't wash). For successful storage, it's essential to cure the onions: Spread them out to dry for a couple of weeks in a warm, airy place, out of rain and sun. Once they're cured, braid the tops or cut them off, leaving a 2.5-centimetre stub. Store at 60 to 70 per cent humidity, as close to 0°C as possible without letting them freeze, in mesh bags or on wire mesh shelves to allow for good air circulation. Check regularly and remove any that are sprouting or rotting.Diseases and PestsOnion root maggots Adult flies lay eggs at the base of young plants. The white maggots burrow into the underground stem, causing plants to wilt and turn yellow. Later generations burrow into the bulbs of larger onions and may cause them to rot. Mulch immediately after planting or, in damp areas, sprinkle the soil with diatomaceous earth. Destroy infested plants and do a thorough fall cleanup.Onion thrips Thrips suck out plant juices, causing silver streaks that develop into silver patches. Serious infestations cause stunted, bleached leaves and plants that ripen prematurely, produce small bulbs and may die. Spray with insecticidal soap. Don't plant onions near fields of alfalfa or grain (alternative hosts for the thrips).Fungal diseases Onions are susceptible to a number of fungal diseases that can damage leaves and bulbs. To minimize problems, plant in well-drained soil, practise a four-year crop rotation and don't water late in the day. Scallions and shallots, where to get them Scallions and shallotsWhile you can get scallions by harvesting nearly any bulb onion early, certain varieties are specially grown for their delicate stems and juicy green tops. ‘White Lisbon', ‘Long White Summer Bunching' and ‘Tokyo Long White' form mild, white scallions. ‘Red Baron' has a white bulb and a red stalk when grown in cool weather (more pink in warm weather), and ‘Deep Purple' is highly coloured at any temperature. Sow seeds outside as early as the ground can be worked, one centimetre apart. Don't thin, as scallions can be harvested when one centimetre or so in diameter. For long, white stems, hill plants up with loose soil as they grow. For an ongoing harvest, make successive sowings.Shallots are gourmet onions with a delicious mild flavour. In spring, plant bulbs 10 to 15 centimetres apart, with the tips just below the soil's surface and the flat ends down. If planted in fall, mulch with 30 to 60 centimetres of hay, straw or leaves in cold areas (pull back mulch in spring). By the time the tops have withered and they're ready to harvest, each bulb will have produced a cluster of six to10 more bulbs. Harvest and store as regular onions. Try ‘Ambition' or ‘Matador'.Winter flavourTo enjoy fresh onion flavour throughout the winter, dig up your chives in fall, plant up in a small pot and bring them indoors. They'll need a cool period of about six weeks in a refrigerator (or an unheated garage). Then place the pot on a sunny window where it will get four to six hours of direct light each day.SOURCES - KEY: ‘Ailsa Craig': 1, ‘Ambition': 2, ‘Barletta': 3, ‘Candy': 4, ‘Copra': 5, ‘Crystal Wax': 6, ‘Deep Purple': 7, ‘Evergreen Bunching': 8, ‘Frontier': 9, ‘Long White Summer Bunching': 10, ‘Matador': 11, ‘Pacific': 12, ‘Red Baron': 13, ‘Red Burgermaster': 14, ‘Redwing': 15, ‘Riverside Sweet Spanish': 16, ‘Super Star': 17, ‘Tokyo Long White': 18, ‘Walla Walla': 19, ‘White Lisbon': 20, Egyptian onions: 21, multipliers: 22.Halifax Seed Co. Inc.: 4, 18. Johnny's Selected Seeds: 1, 5, 7-9, 14, 15, 17, 19. McKenzie Seeds: 3, 8, 13. Richters Herbs: 8, 9, 21, 22. Stokes Seeds Ltd.: 1, 3, 4, 9, 10, 16-20. Thompson & Morgan Inc.: 13, 19, 20. Veseys Seeds Ltd.: 4, 8, 10, 11, 13, 17-19. West Coast Seeds Ltd.: 1, 2, 5, 12, 14, 15, 17, 19. William Dam Seeds: 3-5, 8, 11, 13, 15, 17, 20.