How to Grow Onions

Here are the top tips for growing onions. For more detailed information, keep reading below.

• Sunlight: Plant onions in a spot that gets 6-8 hours of direct sun every day.
• Soil: Use Miracle-Gro Organic™ Raised Bed & Garden Soil for in-ground or raised beds, and Miracle-Gro Organic™ Outdoor Potting Mix for outdoor containers.
• Planting: Space bulbs 6 inches apart for full-sized onions, or 3 inches apart if you plan to harvest some as scallions.
• Watering: Water your onions whenever the top inch of soil feels dry.
• Feeding: A month after planting, begin feeding plants with Miracle-Gro Organic™ All Purpose Plant Food.
• Harvesting: Harvest scallions when their green stems are big enough to eat. For full-sized onions, wait until the tops turn yellow and fall over.

Add some flavor to your garden by planting onions! They're one of the easiest vegetables to grow; the hardest part is choosing which variety you want. Most types, including yellow, white, red, and sweet onions, have the same basic needs. Plus, you can harvest them at different stages: as spring, green onions, small, immature scallions, or as full-sized bulbs. Here’s how to grow onions.



Choosing the Right Onion for Your Area

The trick to successfully growing onions is choosing a variety that suits your region, because onions form bulbs based on how many hours of daylight they receive.

• Long-Day Onions need 14 to 16 hours of daylight to form bulbs. They grow best in northern regions (zones 6 and colder) and should be planted in late winter or early spring.
• Short-Day Onions need about 10 to 12 hours of daylight to form bulbs. They are ideal for southern regions (zones 7 and warmer) and are typically planted in the fall for a late spring harvest.
• Intermediate-Day Onions are also referred to as day-neutral onions. They require between 12 to 14 hours of daylight to form bulbs and can be grown in most zones but perform best in zones 5 and 6. Plant them in fall in mild winter regions, or in spring in northern areas.

Not sure what your zone is? Learn more about growing zones.

Where to Plant Onions

When planting onions, choose a spot with 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 full-sized onion bulbs, 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 outdoor containers with Miracle-Gro Organic™ Outdoor Potting Mix to allow moisture and air to move freely. For in-ground planting beds, mix 3 inches of Miracle-Gro Organic™ Raised Bed & Garden Soil into the top 6 inches of existing soil to improve the growing environment. This organic soil is also perfect for filling raised beds.

How to Plant Onions

Onions are easiest to grow from "sets" or "bulbs," which are essentially tiny onion seedlings. Separate the onions by size. Pencil-size seedlings yield the biggest bulbs, while other size seedlings are better suited for growing scallions.

Plant the bulbs 1 inch deep with the bulb end facing down. Space them 6 inches apart to grow large bulbs. If you want to harvest some as green onions or scallions, you can plant them 2 to 3 inches apart and pull every other one as they grow, leaving the rest to mature into full-sized onions. Water thoroughly after planting.

To grow onions from seed, start seeds indoors 2 to 3 months before your area's average last frost date. Check out seed starting indoors for more information. Once your seeds have grown into young, strong plants, you can follow the planting directions above.

How to Care for Onion Plants 

Once they're in the ground, onion plants are pretty easy to grow and care for. 

• Watering: Onions have shallow roots, so consistent moisture is key to success. Check the soil every few days and water whenever the top inch feels dry.
• Feeding: A month after planting, start feeding your onions with Miracle-Gro Organic™ All Purpose Plant Food, following the label directions. This is especially important when the bulbs start to form and the plants need extra nutrition.
• Mulching: A thin layer of fine mulch (like straw or untreated grass clippings) helps keep the soil moist. Just be sure to keep the mulch pulled back from the tops of the developing bulbs, as they need sunlight to grow properly.

When to Harvest Onions

• For Green Onions or Scallions: You can pull these as soon as the stems are thick enough to eat, which could be as early as 2 to 3 weeks after planting depending on the size of the seedling.
• For Full-Sized Bulbs: Wait until the tops have begun to turn yellow and fall over. At this point, gently bend any remaining stems over and leave the bulbs in the ground for a few more days. To harvest, pull the bulbs free and shake off the excess soil. Let them "cure" in a warm, dry spot with good air circulation for 7 to 10 days. This allows their roots to dry and necks to seal for storage. Once cured, clip the roots and tops, and gently brush any remaining dirt off the bulbs (be careful not to loosen the papery skin).

How to Use Onions in the Kitchen

Homegrown onions add a flavor boost to almost any dish. They are perfect for creating fresh toppings and condiments, like a zesty Fire-Roasted Peach Salsa or a tangy Pickled Summer Relish to enjoy later. Onions are also a key ingredient in many main courses. Try them in Foil Dinners with Chicken, Vegetables & Lager or as part of a flavorful salsa verde to top a Grilled Ribeye.

In the kitchen, a good rule of thumb is to use sweet red onions for raw dishes like salads and sandwiches, and yellow or white onions for cooking. Green onions or scallions are versatile and can be used either way.

Ready to start planting and growing your own onions? With these tips, you’re ready to enjoy a delicious and rewarding harvest.