How to Plant, Grow, and Save Seeds from Onion (Allium cepa)
A culinary staple for many cuisines, onions are an essential vegetable in American gardens. Onions, like other members of the Allium family, are biennials, producing seeds in their second year of growth.
Plant onion seeds indoors 8-10 weeks before transplanting them outside just before the last frost. Sow onion seeds ¼” deep. They will germinate in 4-10 days. Before the last frost, go out to the garden and make a large furrow in the soil, at least 4” deep. Water this furrow before planting your seedlings to make transplanting easier. Set out seedlings 3-6” apart. Plant onion seedlings in the least weedy part of your garden. Onion seedlings are small and do not compete well with weeds.
Several bacterial, fungal, and viral diseases can affect onion growth. Insect pests can also be a problem to various degrees in different parts of the country. Plant your onions in a well drained space. Diseases and fungi such as Fusarium basal rot, white rot, and Botrytis neck rot can affect Allium crops in storage. Crop rotation can help prevent these diseases.
The tops of bulb onion plants fall over naturally once the bulbs have matured. When half of the tops in a planting have fallen over, lift all of the bulbs and place the pulled plants in a warm, dry place, away from direct sunlight, to cure.
Cure onions for two to three weeks after harvesting by storing them in a warm place away from direct sunlight. When the onions feel paper-dry on the outside, clip off the tops and roots, and lightly brush off loose soil before storing the onions in a cool, dry place. Arrange them in a single layer or hang them in mesh bags. Properly cured onions will store for 6-8 months in a root cellar or cool basement.
Eating and Storing
Onions have limitless potential in the kitchen. Most savory dishes can be improved with some simple caramelized onions and sauteed garlic. Onions can be roasted, fried, pickled, sauteed, and combined into dishes in dozens of other ways. Onion jam or compote is a great way to use a flush of red onions that will not store as well as white or yellow onions.
Onion is a biennial crop. Biennial crops typically do not flower in their first growing season. They must first experience cold weather before they flower, set seed, and die in their second growing season.
When saving seeds from onion, separate varieties by at least 800 feet-½ mile in their second year. To ensure viable seeds, save seeds from at least five plants. To maintain a variety over time, save seeds from between 20-50 plants.
To produce seed from onion, select as many perfect onions as you can spare for seed production and store them through winter in a cool, dry, dark place. Replant them in early spring at the same bulb depth and spacing as when they were harvested. After the plants bloom and seed heads begin to dry, gather the heads in a paper bag and shake the seeds free. Allow the seeds to air-dry for a few days before storing the seeds in a cool, dry place. When stored in a cool, dark, dry place, onion seeds will remain viable for two years.