Want big onions? Try starting them from seed
Though it's far too early to start the seeds of warm-season crops, such as tomatoes, basil and eggplants, early February is the perfect time to get started growing onions from seed.
While most of the gardeners I know are used to going to the garden center and purchasing small onion bulbs (called sets) for planting into the garden, research shows that onions grown from seed grow larger than those started from sets.
If you're interested in experimenting in your own garden this year, start some onion seeds in the next week or two and see how they compare to those grown from sets.
To grow onions from seed, start by choosing the right variety. Onions are categorized by how the day length relates to when their bulbs begin to form. Here in Pennsylvania, the best onion varieties for us are known as long-day onions. These varieties form big bulbs here in the north, but won't do well in the south, where they should be planting varieties known as short-day onions. With long-day onions, bulb set occurs when the days reach about 14 hours in length.
Alternatively, we can also grow what are known as day-neutral onions. These varieties aren't as dependent on day length for bulb set and perform well across much of the middle of the U.S.
Once you've selected the variety of onion you want to grow from seed, it's time to get started planting the seeds. Most onion varieties take about three months to mature from seed to harvest. They also enjoy the cool weather of spring, so starting seeds early is essential. Typically they should be started indoors under grow lights about 8-10 weeks before they get transplanted out into the garden in late March or early April.
If you don't have a grow light, a fluorescent shop light fixture hung from the ceiling on chains will do just fine for starting seeds of all sorts. Put the lights about two inches above the tops of the plants and raise the lights up as the seedlings grow. It's also possible to start onion seeds on a sunny windowsill, but this often results in leggy, pale seedlings.
When starting seeds of other garden crops indoors under lights, the lights should be left on for 18-24 hours per day, but having them on that long for onion seedlings can affect the bulb set. Instead, leave them on for only about 12 hours per day.
Plant onion seeds in clean nursery flats using sterile, seed-starting potting mix. Seeds should be buried 1⁄4 inch deep and spaced about a half inch apart. They are very slow to germinate, but having a seedling heat mat underneath the flat will both speed the germination and improve the germination rate (the number of seeds that germinate). Remove the heat mat as soon as most of the seeds have germinated.
Make sure your onion seeds and seedlings stay evenly moist. When the seedlings are between 1 and 2 inches tall, you can transplant them into nursery cell packs or small pots, but this isn't a necessary step, like it is with tomatoes, peppers and many other crops.
Soon after your garden's soil can be worked in the spring and it's no longer wet and sticky, it's time to move your onion seedlings outdoors. Harden the seedlings off by taking them outdoors to a shady spot for a few hours every day for 3-5 days. Then, gradually increase the amount of time the seedlings spend outdoors and the amount of sunlight they receive over the course of a full week. Once they're outdoors full time, it's time to transplant them out into the garden.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.
