Planting onions from onion sets directly in the garden in early spring produces large onion bulbs ready to harvest in the fall. For the ambitious gardener, starting onions from seed inside and transplanting them to the garden is a cost-effective method of starting onions. Onions started inside from seed produce an abundance of tender young onions for use as green onions. If left to grow, these tiny onions mature into large bulbs for harvest and storage in the fall.
Start onions inside eight to 12 weeks before the last expected frost in your area.
Fill trays or cells with moist, sterilized seed starter. Moisten the starter by pouring into a large bowl and adding water. Stir to mix well.
Plant onion seeds to a depth of ¼ to 1/2 inch and press the soil down firmly with your hands. Plant three seeds to a cell or peat pot.
Water to thoroughly moisten the soil and set in a warm location. Bottom heat speeds germination. The top of a water heater provides gentle bottom heat.
Check daily for germination. Onion seeds germinate in five to 14 days, depending on the cultivar and the soil temperature.
Move to a sunny location and keep the tops trimmed to a height of 4 inches. Keep soil moist.
Transplant to the garden when the danger of frost has passed in your area.