Growing Onions in Autumn: A Comprehensive Guide for Planting, Care, and Harvesting

Growing onions in autumn is a rewarding experience, allowing you to enjoy fresh, homegrown onions by the following summer. With their hardiness, onions are perfect for autumn planting, especially if you live in a region with mild winters. Here, you’ll find all the essentials on choosing onion varieties, planting techniques, and ongoing care for a robust harvest.

Why Plant Onions in Autumn?

Planting onions in autumn gives them a head start before winter, allowing them to establish roots while temperatures are cool. As spring arrives, the onions resume growing quickly, resulting in larger bulbs by the end of the season. If you have mild winters, autumn-planted onions can also overwinter successfully, offering a head start in growth compared to spring planting.

Types of Onions to Grow in Autumn

Onions come in three main types that can be suited to different growing conditions:

1. Short-Day Onions: Best for regions with mild winters, these onions start forming bulbs when days are 10–12 hours long. Varieties include ‘Texas Early Grano’ and ‘Yellow Granex’.
2. Intermediate-Day Onions: Good for regions with slightly colder winters, these onions need 12–14 hours of daylight to begin bulb formation. Popular varieties are ‘Candy’ and ‘Red Burgundy’.
3. Long-Day Onions: Suitable for northern climates, these onions require 14–16 hours of daylight to bulb, making them ideal for planting in cooler areas. Examples include ‘Walla Walla’ and ‘Yellow Sweet Spanish’.

Steps for Planting Onions in Autumn

1. Select a Sunny, Well-Drained Location
   Onions need full sun, at least 6–8 hours of direct sunlight daily. They prefer loose, fertile soil with a slightly acidic to neutral pH (6.0–7.0). Good drainage is essential to prevent rot.
2. Prepare the Soil
   Loosen the soil to about 8–10 inches deep and incorporate compost or a balanced organic fertilizer to enhance soil fertility. Remove weeds or debris that could compete with onions for nutrients.
3. Plant Onion Sets or Seeds
   Onion sets (small bulbs) are easier and faster to grow than seeds, but both can be used. Plant each set or seed about 1 inch deep, spacing them 4–6 inches apart in rows that are 12 inches apart.
4. Water After Planting
   Water the onion sets or seeds thoroughly after planting. Onions prefer consistent moisture, especially in the initial stages of growth, so water them regularly, avoiding overly wet conditions.

Caring for Onions Over Winter and Spring

• Mulching: Mulching with straw or leaves helps retain moisture and insulates the soil, which is beneficial in colder regions. It also suppresses weeds.
• Fertilize in Early Spring: Onions benefit from a nitrogen-rich fertilizer applied in early spring as new growth begins.
• Monitor for Weeds: Onions are shallow-rooted, so they can easily compete with weeds. Regular weeding is essential to ensure they have ample access to nutrients.

Harvesting and Storing Onions

Onions are usually ready for harvest in late spring or early summer when the tops begin to yellow and fall over. Stop watering at this stage to help the bulbs dry out for harvesting.

1. Harvesting
   Gently pull the onions from the soil, being careful not to bruise them. Lay them out to dry on the soil for a day or two if weather permits or move them to a dry, ventilated area indoors.
2. Curing
   Cure the harvested onions by laying them in a single layer in a warm, dry area out of direct sunlight for about two weeks. This process ensures the onions store longer by drying the outer layers and necks.
3. Storage
   After curing, trim the tops and roots. Store onions in a cool, dark, and dry place. Long-day onions tend to store well, with proper storage extending their shelf life for several months.

Top 10 Questions and Answers on Growing Onions in Autumn

1. When is the best time to plant onions in autumn?
Plant onions 4–6 weeks before the first frost date to give them enough time to establish roots.

2. Can I plant onions in containers?
Yes, onions can be grown in containers at least 10–12 inches deep with good drainage.

3. How deep should I plant onion sets?
Onion sets should be planted about 1 inch deep, with the tip slightly exposed.

4. How do I know which onion variety to choose?
Choose based on your region’s daylight length. Short-day onions are ideal for the south, intermediate for central regions, and long-day onions for the north.

5. Should I fertilize onions after planting?
Yes, onions benefit from a nitrogen-rich fertilizer in early spring, as they need high nutrients for good growth.

6. How much water do onions need?
Keep the soil consistently moist but not soggy, especially during early growth and dry spells.

7. Can I use grocery store onions for planting?
It’s best to use certified seed onions or sets to avoid potential growth inhibitors on grocery store onions.

8. Why are my onion bulbs small?
Small bulbs may result from poor soil nutrition, insufficient sunlight, or crowded planting.

9. How do I prevent onion pests and diseases?
Rotate crops yearly and avoid planting onions in beds previously used for other alliums to reduce disease risks.

10. How do I store harvested onions?
Store cured onions in a cool, dark, and dry place. Avoid refrigeration as it can cause sprouting.

This guide equips you with the knowledge needed for a successful onion-growing season, from planting in autumn to enjoying your homegrown onions all year long!