We start growing onions earlier than any other garden plant. Our first set of onion seeds get planted in early February and grown indoors for about 8 weeks before being set out in the garden in early April. This spring we’ll plant 4 flats of 72 onions each. Like most our garden plants, onions are planted in a steril seed starting mix and bottom watered only. As soon as the seeds germinate the clear cover comes off and the seed start mix is allowed to dry slightly between waterings.
As the onion seedlings grow, but before they are set in the garden, they’ll start to tip over, producing quiet a tangled mess. Its best to use scissors to cut them back and then keep them about 4 inches tall.
We start harvesting the onions as scallions as soon as we can. So quiet a few of the onions will not reach maturity. In fact, the first planting will be harvested as the summer progresses. None will be used for storage.
A second crop will be direct seeded in mid-April with the hope of harvest in late fall – just in time for storage. Instead of the sweet varieties planted in February, the second, direct planting, will be storage types. If stored correctly, these storage varieties should last all through the winter and into the early spring when the walking onions will be available in the perennial garden.
In the midwest we can plant long day and intermediate day onions. Short day onions – which are sold as both seeds and plants (bunches) will not produce usable bulbs.
Onions are cool weather plants so there is no reason to try to warm the seeds for germination. Very bright but cool light can be supplied by florescent shop lights set very close to the onion seedlings.