I fell in love with onions for the first time when we began growing “Walla-Walla Sweets,” an onion you can eat like an apple. We began with 2,000 at our farmstand in Massachusetts, doubled that the following year, and finally found the “glut” level at 6,000 onions per season. These aren’t available at stores, so once word got around customers would come by just for the the onions (and then pick up a few other things. Heh.)
Onions are easy to grow from seed, or more expensively from sets (the little bulbs with no tops, the size of a dime) or plants (the bunched plants with tall tops). I’ve found that seeds and plants are the most successful. But the first thing to know is which variety to grow, and that depends largely on where you live.
Short day/long day: You wouldn’t think this, but summer days are much longer in the north than in the south – at least an hour or more—and the dividing line is roughly 36˚ latitude, more or less, depending on onion variety. Long-day varieties (such as Walla-Walla) need up to 14 hours of sunlight to mature, whereas short-day onions need equal amounts of dark and light.
The reason is this: Onions don’t begin to form bulbs until their tops are fully mature. The bigger the top, the bigger the bulb will be. The top stops growing when the bulb begins to form, and that change is triggered by day length. A short-day onion (such as Videlia), if grown up north, would bulb up too early and stay small. If a long-day variety were grown in the South, they wouldn’t get enough daylight to trigger the bulbing process. I know. I learned it the hard way in Tennessee, where we ended up selling Walla-Wallas as sweet scallions. Cripes.
Seeding: Sow seeds inside at least 8 weeks before average last frost, and sow them densely (1/4 to ½-inch apart) for two reasons. First, onion roots separate readily for transplanting and don’t mind the close spacing when small. Second, you can grow four onions in a bunch, rather than in a row 3-4 inches apart. More on that in a moment. I grow them in our own potting soil (see “Potting Soil” entry), and trim the tops the tops back to 3- 4” when they get tall and start to fall over. The clippings can be snipped into small pieces and dried. Harden off your seedlings by exposing them to above-freezing night temps for about a week, then plant any time after average last frost date.
In areas where winters are not severe, onions may be seeded outdoors in the fall when there’s little or no weed competition, resulting in a crop of larger, sweeter onions the following summer.
Growing: Onions need full sun and fertile well-drained soil. Sandy loam is ideal. If your soil puddles up in a heavy rain, that’s not a good spot. They’re shallow-rooted, and need an inch of so of water per week. Most gardeners space their onion plants 3-4 inches apart in rows one foot apart (for large onions such as Ailsa Craig give them 5” spacing or more), and this works. Others plant 3-4 inches apart in staggered rows in wide beds, and this also works. Both systems make the onions hard to weed without pulling by hand, however, so I put four transplants together, spacing each group a foot apart in squares. The onions grow as they normally would because, while grouped together, they have plenty of space around them. AND, I can take a scuffle hoe and cultivate easily in both directions.
Remember to feed (if necessary) and water your plants early to encourage large tops as soon as possible. Once bulbing begins, the bulb’s size is determined by the top’s size, and there’s no need for fertilizer or soil amendments after that.
Harvest when the tops are falling over. Pull bulbs gently out of the soil and let them sun-cure, exposed for at least a week with the tops on – or in a warm, dry spot if it rains. Then either cut the tops off for sweet onions which don’t keep long, or leave them on and braid storage onions to hang in the kitchen.
Health. Onions are rich in potassium, vitamin C, fiber, and cancer-fighting antioxidants.
Storage: Sweet onions won’t store well, so whatever we don’t eat or sell, or make fried onion rings out of, we chop up and freeze in labeled freezer bags.