Onions can be grown from seeds, sets (small bulbs) or transplants. Sets and transplants are easiest.
Prepping:
Choose a garden area that gets several hours of direct sunlight. Onions like to be planted in slightly acidic, loose soil. To prepare for planting, work in some compost or soil building conditioner and a general-purpose fertilizer for acid-loving plants like blueberries and rhododendrons.
Planting:
Onion sets and transplants should be placed 4-6″ apart unless you plan to harvest them early and use them as green onions. Plant them no deeper than 1” below the soil. If your onions are already sprouting, do not bury any of the new growth emerging from the bulb.
Growing:
During the growing season, water plants when the soil is dry up to your first knuckle and apply a high nitrogen fertilizer regularly. Stop applying fertilizer when you can tell the plants are starting to bulb.
Harvesting:
When the leaves of the onion start to turn yellow and begin to fade, the time is right to dig up your onions. You can use them immediately or you can let them dry outdoors for a week to cure before storing them. Remove leaves before storing them in a cool, dry, dark place.
Shallots:
Grow them just like onions but plant shallots only 2” apart.
Leeks:
Grow them just like onions, but plant them deeper. Just the tip of the newest leaf needs to be visible. You can begin harvesting leeks as needed after just 30 days.