Onions are a versatile vegetable that can be grown in spring or fall gardens. Planting onion sets in the fall allows the bulbs to develop their roots through the winter and be ready for rapid growth and bulbing when spring arrives. Determining the optimal planting time for fall onions ensures the best chance of overwintering success and a bountiful harvest.
Why Plant Onions in the Fall?
Fall planting of onion sets has several advantages over spring planting:
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Onions establish roots and leaf growth during cooler fall temperatures, leading to bigger bulbs when they mature in summer. Spring-planted onions often bolt in hot weather before fully bulbing
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Fall-planted onions get a head start on spring weeds The onion roots become established when fewer weeds are germinating
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Garden beds are often less crowded in fall compared to spring when many warm season crops are planted. This makes fall planting easier.
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The onion bulbs mature when temperatures are ideal in early summer rather than during mid-summer heat.
When to Plant Fall Onion Sets
The ideal planting window for onion sets is 4-6 weeks before the average first frost in your area. Onions need time to establish roots before winter but want to avoid too much top growth that can be damaged by hard freezes.
Using this guideline, here are some general planting timeframes for various regions:
- Northern states and Canada: Late August to mid September
- Mid-Atlantic and Mountains: Mid September to early October
- Southern States: Late October to mid November
- Pacific Northwest: Late September to mid October
- Southwest: Late October to mid November
Check local frost dates and back calculate 6 weeks to determine your ideal planting window. Choose a short-day onion variety suited to your latitude.
How to Plant Onion Sets in Fall
Follow these simple steps for proper planting of onion sets:
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Prepare beds and loosen soil at least 6 inches deep, removing any debris. Mix in 1-2 inches of mature compost.
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Create trenches 1-2 inches deep and space them 6-12 inches apart.
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Place onion sets 1-2 inches deep and 4-6 inches apart in the trench. Cover with soil.
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Water the planted onions well and begin regular watering. Proper moisture is key for good establishment.
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Add a 2-4 inch layer of straw mulch over the soil after sprouting to retain moisture and regulate soil temperature. Replenish as needed.
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In very cold climates, increase mulch to 6 inches in late fall once ground has frozen.
Caring for Onions Over Winter
Onions are quite hardy but need a little care to make it through winter:
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Use row cover or cloches if temperatures will be below 10°F for extended periods.
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Avoid excessive nitrogen fertilization in fall and winter, as it leads to lush foliage vulnerable to frost damage.
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Monitor soil moisture and water during dry spells. Most winter damage occurs from desiccation.
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In spring, remove any winter mulch when new growth resumes. Weed and water as needed.
Choosing the Best Onion Varieties
Look for short or intermediate day onions suited for your latitude:
- Short day – ‘Texas Grano’, ‘Yello Granex’, ‘Candy’
- Intermediate – ‘Red Bull’, ‘Red Zeppelin’, ‘Sterling’
- Long day – ‘Copra’, ‘Trophy’, ‘Red Wing’
Within each daylength range, choose disease-resistant, pungent varieties proven in your climate. Sets labeled simply “onion” are often long-day types.
Troubleshooting Common Onion Problems
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Small bulbs: Overcrowding, insufficient watering, or planting too late are likely causes. Thin carefully next time and follow regional planting guidelines.
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Bolting: Onions prematurely send up a flower stalk when stressed by extreme cold, heat, drought, or overcrowding. Keep them healthy and content!
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Rot during storage: Insufficient curing or storing at too high humidity causes decay. Cure bulbs fully.
Enjoying the Onion Harvest
With proper fall planting and care, you can enjoy harvest up to 4 weeks earlier than spring-planted onions! Use fresh onions soon after harvest in salsa, salads, and other warm weather dishes. Store dried bulbs in a cool, dry area in mesh bags. The autumn tending pays off with sweet onions through the next summer.
Best Onions for Fall Planting
Onion sets are widely available in spring, sold as yellow, white, or red, and often not identified by variety. Try searching online or in garden catalogs to find sets or slips for autumn planting.
Look for varieties most successful in your growing zone. Onions are categorized as short-day, intermediate, or long-day. Keep in mind that sets need 80 days and slips need up to 110 days to mature from the time theyre planted.
Here are a few onion varieties to consider for autumn planting.
- Electric: Winter hardy with shiny red skin and pink-tinged flesh. Mild, sweet flavor.
- Radar: Yellow, globe-shaped Japanese variety. Mild flavor and good bolt resistance.
- Snowball: A short-day variety with medium-sized, slightly flattened bulbs. A mild but tangy onion best for eating fresh.
- Granex: Large, globe-shaped bulbs are mild and sweet. A short-day variety and a popular choice for southern gardens.
- Walla Walla: Extra large bulbs mature in 90 days. This long day type is comparable to Vidalia onion in flavor.
How to Plant Onions in Fall
Both sets and slips (young plants) need four to six weeks to establish tops and roots before frost sets in. Find the first frost date in your zone and back time to find out the best day/s for planting.
- Start by digging a trench 2 to 3 inches deep and 2 inches wide.
- Fill the bottom of the trench with an inch or two of well-aged compost.
- Place the sets or slips about 1/2 inch into the compost layer allowing 4 to 6 inches in between each onion. Place sets with the pointed end facing up.
- Fill the rest of the trench with soil, covering the onion with about 1/2 inch of soil. If you start with slips, leave any green tops above the soil surface.
- Water and mulch with a thin layer of straw or dried leaves.
- Once new green growth appears, add more mulch and continue to water every few days. Youll need a mulch layer of at least 6 inches to protect roots when ground freezes.
Planting Autumn Onion Sets With Emily Cupit
FAQ
When should I plant onion sets in the fall?
Choosing the Right Time to Plant Timing is crucial when planting onion sets. Aim to plant them in late August or early September. This gives the onions enough time to establish their root systems before the colder temperatures set in.
How late in the season can you plant onions?
For fall plantings for a spring harvest next year, you can plant seeds in late summer (6-8 weeks before your first frost) or plant seeds or starts in early …
Which month is best to plant onions?
| Season | Time of seed sowing |
|---|---|
| Tamil Nadu, Karnataka and Andhra Pradesh | |
| 1. Early Kharif 2. Kharif 3. Rabi | Feb.-April May-June Sept.-Oct. |
| Rajasthan, Haryana, Punjab, UP and Bihar | |
| 1. Kharif 2. Rabi | June-July Oct.-Nov. |
Can I leave onion sets in the ground over winter?
Many times these small onions will cure right in the ground. They can stay buried in summer’s dry soil without any indication until fall — or even next spring — and then come up. Many times I’d see them and leave them in the ground on purpose as my back-ups for spring onions during the fall and winter months.
Should you plant onions in autumn?
Onions will also do their thing for you if you can find a spot on the plot that gets lots of sun and has rich, free-draining soil. Onions are a cool weather crop that can be planted in fall or early spring for harvest through winter. Getting the timing right for planting onion sets in autumn is key to growing large, healthy bulbs.
How do you grow autumn onions from sets?
Follow our guide to growing autumn onions from sets. How to plant onion sets – preparing the soil. Prepare the soil well by removing weeds and raking level. Add a slow-release fertiliser if necessary. Use your trowel or hoe to make a drill that is deep enough to sit the onion sets, with just the papery tops above the surface.
Are autumn onion sets easy to grow?
With just a little bit of effort, you can enjoy fresh, homegrown onions all winter long. Autumn onion sets are a great way to grow onions at home. They are planted in the fall, and they will mature the following spring. Autumn onion sets are easy to grow, and they produce a good harvest. To plant autumn onion sets, you will need: Instructions: 1.
How deep should autumn onion sets be planted?
A: You should plant autumn onion sets about 1-2 inches deep. If you plant them too deep, they may not grow well. If you plant them too shallow, they may be exposed to frost and damage. Q: How far apart should I plant autumn onion sets?
When do onions grow?
Onions form bulbs when daylight length shortens in late summer and autumn. Planting sets mid-fall allows enough time for roots to establish before winter so bulbs can swell rapidly in spring as days start to lengthen again. The result is large, juicy onions ready for harvest before summer heat causes them to bolt.
Can you plant onion sets in winter?
Make sure that you plant onion sets in soil that drains well and doesn’t get waterlogged through winter. Onion sets for autumn planting are hardy but winter wet can cause them to rot. If you have raised beds, these will be ideal for planting onions because of the improved drainage. How do I plant onion sets?