It seems too early to be vegetable gardening, but experienced gardeners have their onions in the ground by St. Patrick’s Day. Onions and shamrocks are perfect together! In order to get fat onion bulbs, you need to grow big healthy tops before the days get long. That’s when the plants switch from growing foliage to storing food in the bulbs, so planting too late means puny bulbs at harvest time.
The easiest way to grow onions in the home garden is by planting onion “sets”, tiny onions that grow into big onions. These are widely available, usually in bulk by the pound. All you need to do is loosen up a patch or row with a cultivator, mixing in some 10-10-10 fertilizer, and then press the little onions into the loose soil two inches deep and two inches apart. We recommend “wide row” planting; instead of a single line plant six or eight rows a few inches apart. Onions don’t mind being crowded, and later you can thin the weaker plants and have plenty of fresh scallions. Make sure to tamp the soil over your onion sets.
Onion transplants grow the biggest sweet onions. You might be able to find these locally; if not you can get them online from Brown’s Omaha Plant Farm (https://www.bopf.com). Onion plants come in bunches of about 60-70 plants, each the size of a pencil. They’re already growing, so they take off like crazy as soon as you plant them. Starting with onion transplants gives you a “head start”, insuring you’ll get the biggest, fattest sweet slicing onions within the growing season. Two tips for the biggest onions: always trim off the tips when planting, and plant them as shallow as possible (one inch deep).
Onions need fertilizer three or four times before harvest. Use 10-10-10, sprinkling the fertilizer around the base of the plants (fertilizer dust can scorch the foliage). Super-phosphate and bone meal are good for onions too. Fertilize when plants reach 6 inches, and again every two or three weeks. The best way to fertilize onions is by “side dressing.” This means sprinkling fertilizer at the base of the plants, taking care not to get fertilizer dust on the stalks, where it can burn.
Thin every other plant, harvesting the weaker ones. Big, healthy tops mean big fat onions. Pinch off any seedpods, because if the plants set seed they won’t grow big bulbs. Once the days are long enough, healthy vigorous onion plants “shift gears” and energy from the big tops is transported down to make a bulb. Bulbs continue to grow until the tops wither and turn brown. That’s the best time to harvest.
If your garden is too gooey to plant, try making some fluffy dirt just in the onion rows: Sprinkle 10-10-10 fertilizer and a little superphosphate on the row and then spread three inches of peat moss. Till the row six inches deep, trying not to step on the freshly tilled dirt. Rake it smooth. Magic. Now you can tuck in your onion sets easily. Next tamp the soil gently. You’re done, and right on St. Patrick’s Day schedule!
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers.” “Let’s Grow” is published weekly; column archives are on the “Garden Advice” page at www.goodseedfarm.com. For more information is available at www.goodseedfarm.com or call GoodSeed Farm Landscapes at (937) 587-7021.