The last two days I have been seeding onions. Like most growers, I started out growing onions from sets, which are small, immature onion bulbs. They were easy to grow, but now I want to expand my variety horizons, but with onion sets, choices were limited. So this year I turned to seeds. Growing from seed lets me pick varieties to suit the needs of our customers—such as the desire for an early-season sweet onion or a late-season keeper. Colors range from dashing purple to pure white and numerous shades of yellow. Shapes and sizes vary, too, from the bottle-shaped ‘Italian Torpedo’ to the plump perfection of ‘Ailsa Craig Exhibition’.
Most onion experts agree that, diversity aside, onions grown from seed perform better than those grown from sets. They are less prone to disease, they store better, and they bulb up faster, and there is less double bulb heads.
Onion varieties differ in the length of daylight and the temperature required to make a bulb. Short-day types are ideal for the South, where they grow through cool southern fall and winter months. They’re triggered to bulb by the 12 hours of sunlight that come with the return of warm, early summer weather.
Long-day onions are best grown in the North, where the summer daylight period is longer. These onions require at least 14 hours of light to bulb up. The plant grows foliage in cool spring weather, then forms bulbs during warm summer weather, triggered by the long days. Our farm is located in the north, so long day onions are the type we will be growing.
I sow seeds 1/4 inch deep in flats filled with soil-less potting mix. I place the flats on the seeding rack in our seed room. Onions germinate in just a week at around 70°F. Once they have produced 3-5 leaves I move the flats to to a low rack near the floor in the seed room where it is cooler. They remain under fluorescent lights, one warm white and one cool white bulb per fixture. I keep the lights just above the leaves, adjusting the lights as the plants grow. I feed the seedlings with a water-soluble fertilizer at half strength every other time I water, being careful not to keep them too wet. Once the weather gets a little warmer outside, I move them to the cold frame. They remain there until they are transplanted into the field.