Climate: All climate zones are suitable, but plant the different types at the right time of year for best results.
Planting: Sow seed or plant seedlings 8cm apart. Water seeds in and mulch with compost to conserve soil moisture and to prevent surface crusting. Plant a 6-9m long row of the long-keeping types, about half that for the others. You can plant the short-keeping types in batches. In tropical, humid and dry subtropical and semi-arid areas, plant long-keeping onions in autumn, elsewhere from autumn to midwinter. Start spring onions and those not meant for storage any time except where frosts are sharp. In those areas, avoid planting in coldest months. Don't plant in soil with a lot of recently added organic matter.
Growing: Keep the soil moist and feed plants every few months with low-nitrogen complete plant food. Stop watering long-keeping onions as they approach maturity. Onion fly, which destroys the bulbs, is encouraged by excessive organic matter. Thrips may damage growth and downy mildew is a common disease. Don't allow weeds to establish around onions; pull them out when first seen.
To harvest, pull spring onions and non-keeping onions as needed. Long-keeping onions are matured in the ground and pulled when the tops die back. Dry them thoroughly in the sun before storing them.
Garlic is propagated from store-bought bulbs.
Climate: Not critical. Treat as an annual.
Planting: The plant must be propagated from the cloves. Plant in autumn or spring, 8cm deep and 15cm apart.
Growing: Keep the soil moist and feed plants every few months with low-nitrogen complete plant food. The bulbs are ready to harvest about six to eight months after planting when the top growth becomes dry and falls over. Stop watering as plants approach maturity. Pull out mature bulbs and leave to dry in a cool, airy place. When dry, braid the tops together and hang to dry out further. In warm climates, autumn plantings should be mature by the following summer. Cool-climate spring plantings may take two growing seasons to produce good cloves.
Mound soil around leeks to keep their stems white.
Climate: Suitable for all zones.
Planting: Leeks have a long growing season and are usually grown from seedlings. Drop each seedling into a 15cm-deep hole so the tops just protrude. Don't fill in the holes but water well. This method helps develop the long, white stem. Make holes every 15-20cm along a 2-4m row (stagger the plantings for a longer season). Soil must be enriched with compost and well-rotted manure. In tropical and dry subtropical areas, plant in autumn. In temperate and cool temperate climates, plant from late spring until early autumn and in all other areas plant from midsummer to late autumn.
Growing: Keep evenly moist and feed every two months with a ration of complete plant food. As the stems grow, mound soil around them to keep them white. They may be troubled by onion thrips (hose them off) but are usually pest-free.
To harvest, pull when the stems are of a suitable size. Don't let them get too fat or they become tough.
Shallot (French or golden)
Climate: Grows in all zones.
Planting: Push individual cloves just beneath the surface, pointy end up, and about 20cm apart. Do this in late autumn or winter except in the colder parts of cool temperate areas where early spring planting is better. The bulbs form clumps like garlic and about a dozen plants is enough for starters. Plant into any well-drained, reasonably fertile soil.
Growing: Keep the soil moist while the plants are growing but stop watering when the plant is fully mature and the leaves are beginning to yellow.
Harvest when the tops of the plants die back. Lift the whole knob and dry it in the sun before storing.
Source: Gardening: A Commonsense Guide (Murdoch Books)