Onions (Allium cepa) are one of the hardiest and easy-growing plants for the vegetable garden. Planting onion bulbs, or more commonly referred to as onion sets, is the fastest method for growing onions, which decreases the time from planting to harvest. A few popular varieties of yellow onions include Yellow Globe, Copra and Sweet Sandwich. Once harvested, yellow onions can be stored for several months in a cool, dark place.
Select a garden site that receives full sun all day long, preferably up to 12 hours. Clear the area of weeds.
Work the ground after the last frost by digging or raking it to loosen the soil and remove large clods. Yellow onions grow best in a neutral pH soil. Add organic material to the soil and mix in well.
Dig trenches that are about 2 inches deep and spaced 15 inches apart. Place yellow onion bulbs or sets into the trenches with the root ends down and space 4 inches apart. Cover with enough soil just to cover the bulbs; firm over with a hoe.
Water the onion bulbs well after planting and keep watered three to four times weekly for the first two weeks after planting. After that, water once a week. Use a soaker hose for deep watering and to keep the foliage dry as it emerges.
Apply mycorrhizal fungi as a fertilizer for the onions right after planting. This fungi attaches to the roots to help the plant absorb water and nutrients from the soil. After this first initial feeding, apply again a month later in late spring to early summer, then stop.
Add a 1- to 2-inch layer of organic mulch around the plants once the tops of the onions appear, about two weeks after planting. Use shredded bark, chopped leaves or organic compost. This helps to control weeds and maintain moisture in the soil.
Harvest onions in late summer, about three months after planting, when the tops are turning yellow. Break the tops of the plants to help the onions begin ripening by stopping their growth. Harvest onions before they produce flower stalks. Harvest the onions in the early morning and lay them in a shady area for two to three days to air dry.