How to Grow Onions
Add some spice to your garden by planting onions. The trickiest part is choosing which varieties to grow. Learning how to grow onions takes little effort, as they're one of the easier vegetables to raise.
Here are our top tips for growing onions.
When planting onions, choose a spot in full sun. For growing onions in pots, select a container based on the type of onion. For onions you plan to harvest as scallions or spring green onions, an 8-inch (or larger) pot works fine. To raise bulb onions, you'll need a container wide enough so that each onion has about 3 inches of space around it. Many gardeners choose to grow onions in plastic tubs or half whiskey barrels.
Select soil that provides a well-drained, nutrient-rich base. Fill containers with light, fluffy Miracle-Gro® Potting Mix to allow moisture and air to move freely. For in-ground planting beds, mix 3 inches of Miracle-Gro® Garden Soil for Vegetables and Herbs into the top 6 to 8 inches of soil to improve the growing environment. If you're planting onions in raised beds, fill beds with equal parts garden soil and potting mix for just the right soil weight.
The right time for planting onions depends on what type you're growing. Onions form bulbs based on how many hours of daylight they receive. "Long day" onions need 10 to 14 hours of daylight to trigger bulb formation. "Short day" types need 10 hours for bulbs, and "day-neutral" types form bulbs regardless of day length. Long day onions grow best in zones 6 and colder, with planting occurring in late winter to early spring. Choose short day onions for zones 7 and warmer, planting in the late fall or early winter for a late spring harvest. Day-neutral onions grow in any zone, but perform best in zones 5 and 6. Plant these in fall in mild winter regions, or in spring in northern areas. (Not sure what your zone is? Learn more about growing zones.)
When growing onions, it's easiest to start with seedlings, which are usually sold in bare-root bundles and referred to as "sets" or "bulbs." Separate the onions by size. Pencil-size seedlings yield the biggest bulbs, while larger and smaller seedlings are better suited for growing scallions. Space individual bulbs 6 inches apart. If you plan to harvest scallions, space bulbs 2 to 3 inches apart, and pull "extra" onions as scallions to achieve a final 6-inch spacing. Plant onions 1 inch deep with the bulb end facing down. To grow onions from seed, start seeds indoors 2 to 3 months before your area's average last spring frost date. Use Miracle-Gro® Seed Starting Potting Mix for best results.
Water thoroughly after planting onions.
Consistent soil moisture is the key to growing onions successfully, thanks to their shallow roots that aren't very efficient at absorbing water. Check soil every few days; when it feels dry down to 1 inch deep, it's time to water.
Mulch helps protect onions' shallow roots from drying out, but just add a thin layer. Keep mulch pulled back from developing bulbs, which grow best when they're exposed to sunlight. Use a fine mulch material, like untreated grass clippings, pine straw, or wheat straw.
A month after planting, begin feeding growing onions with Miracle-Gro® Water Soluble All Purpose Plant Food this is especially important when bulbs are beginning to form and plants need extra nutrition. Follow label instructions to know how much and how often to apply.
Pull green onions or scallions as soon as stems are big enough to eat. With large seedlings, this could be as early as 2 to 3 weeks after planting. For full-size bulbs, wait to harvest until plant tops have begun to turn yellow and fall over. At this point, the tops of the bulbs should be above the soil. Gently bend remaining stems over, let bulbs remain in soil for a few days, and then harvest. Pull bulbs free, shake off excess soil, and let bulbs cure by setting them in a warm, dry spot with good air circulation. (The bulbs need time for their necks to seal for storage and their roots to dry up.) After 7 to 10 days, clip roots and tops, and lightly brush dirt off bulbs. Be gentle, you don't want to loosen papery skin layers. The onions should not have an oniony odor.
Store cured onions in a cool, dry place. Sweet onions keep best in the refrigerator and should be used within a few weeks of harvest. Other bulb onions can store for up to 10 to 12 months.
In the kitchen, grab the right onion for the job: sweet reds for raw uses and yellow or white for cooking. Green onions or scallions can be used either way. Onions go with just about everything and provide the starting point for many dishes.
Ready to start planting and growing your own onions? Click on any of the product links above for more information, to purchase the product online, or to find a retailer near you.