How to Grow Onions: A Simple Guide to Planting and Harvesting

Onions are a rewarding and relatively easy vegetable to grow at home. Whether you prefer sweet, sharp, red, or yellow onions, this guide will walk you through the process from planting to harvest. Let's get started!

Choosing Between Seeds and Sets

Onions can be grown from seeds or small bulbs called "sets." For beginners, onion sets are recommended because they are easier to grow, give you a head start on the season, and have a higher success rate. Onion sets look like small bulbs and can be found at gardening stores. In just 14 weeks, they mature into full-size bulbs. Choose sets with bulbs that are 3/4 inch in diameter; larger ones tend to produce stiff necks and go to seed.

Planting Onions

Location and Soil

Onions need full sun and well-draining, loose soil—sandy-loam to silt-loam is ideal. Avoid heavy clay or compact soil. Mix aged manure or compost into the soil in the fall or early spring to improve texture. The soil pH should be between 6.2 and 6.8.

When to Plant

• Sets: Plant directly into the ground in early spring, 2 to 4 weeks before your last expected spring frost date.
• Seeds: Start indoors 8 to 10 weeks before your area’s last spring frost date. Transplant seedlings outdoors when the soil is workable, about 2 to 4 weeks before the last spring frost. Onions require soil at least 50°F (10°C) to germinate.

How to Plant

• Indoors: Use a shallow tray filled with compost. Plant seeds 1/4 to 1/2 inch deep or set bulbs so the pointy end is just above the soil. Water lightly and place in a warm, well-lit spot.
• Outdoors: Bury sets 1 to 2 inches deep and 2 to 6 inches apart. If direct seeding, sow seeds 1/4 to 1/2 inch deep. Thin seedlings to 3 to 4 inches apart. Space rows 12 to 18 inches apart. Mulch with straw to retain moisture and suppress weeds.

Growing Onions

Onions are heavy feeders and require constant nourishment. Fertilize every few weeks with nitrogen to promote large bulbs, stopping when bulbing starts. Water about 1 inch per week, including rainwater. More water will yield sweeter onions. To deter bolting, water frequently during hot spells.

Container Gardening

Onions can also be grown in containers at least 10 inches deep. Use a well-draining potting mix rich in organic matter. Place the container where it will receive maximum sunlight.

Types of Onions

Onion varieties are categorized as "long-day," "short-day," or "day-neutral," depending on the daylight hours needed to trigger bulb formation. Choose the type that best suits your region:

• Short-day onions: Best for southern regions, start bulbing with 10 to 12 hours of daylight.
• Intermediate/day-neutral onions: Suitable for middle U.S. states, start bulbing with 12 to 14 hours of daylight.
• Long-day onions: Ideal for northern states, start bulbing with 14 to 16 hours of daylight.

Harvesting and Storing Onions

Harvesting

Onions are ready for harvest when the tops turn yellow and begin to fall over. Bend the tops down to speed ripening. Harvest in dry weather by late summer. Handle carefully to avoid bruising.

Storing

Cure onions by setting them on dry ground or in a protected place like a garage or barn. Once cured, store in a cool, dry, well-ventilated area. Ideal storage temperature is 40 to 60°F (4 to 15°C). Check periodically for sprouting or rotting and remove affected onions.

FAQs

Q: Can I grow onions from sprouted onions?
A: Yes, you can plant a sprouted onion, but you won’t get more onions from it. You will get green sprouts, which are tasty and can be used in cooking.

Q: How do I prevent onion diseases?
A: Practice crop rotation and avoid planting onions in the same location year after year. Ensure well-draining soil and proper spacing to reduce disease risk.

Q: Can I grow onions in containers?
A: Absolutely! Use a container at least 10 inches deep with a well-draining potting mix. Ensure the container receives maximum sunlight.

Q: How often should I water my onions?
A: Water about 1 inch per week, including rainwater. More water will produce sweeter onions.

Q: What is the best time to plant onion sets?
A: Plant onion sets in early spring, 2 to 4 weeks before your last expected spring frost date.

By following these simple steps, you can enjoy a bountiful harvest of homegrown onions. Happy gardening!