Starting Onions from Seeds Indoors
Try growing your own onion transplants from seeds started indoors. You will find a greater selection of varieties than those sold as transplants and sets.
Select short day onion varieties if gardening in the south, long-day varieties for northern areas, and day-neutral for all but South Florida and South Texas.
Purchase fresh seeds each year for the best germination. Start seeds indoors 10 to 15 weeks before you plan on moving them into the garden. Plant onion seeds ¾” deep in a clean container filled with a well-drained potting or seed starting mix. Keep the mix moist and move the plants under artificial light or in a sunny window as soon as green appears.
Keep lights 4 to 6” above the plant, on for 12 hours a day, and growing temperatures between 55 and 65 degrees for stouter growth.
A bit more information: Here are a few onion varieties to consider. Short-day onions like Georgia Sweet and Sweet red form bulbs with 10 to 12 hours of daylight. This makes them a good choice for southern gardeners. Long-day onions like Walla Walla and Yellow Sweet Spanish form bulbs with 14 to 16 hours of daylight – perfect for northern regions. Day-neutral varieties like Candy Onion form bulbs with 12 to 14 hours of sunlight and can be grown in all but south Florida and South Texas.