Winter Onion Planting Calendar: Month-by-Month Guide

Introduction

Onions are one of the most useful and reliable crops for UK gardeners. They store well, feature in countless recipes, and are simple to grow even for beginners. One of the best ways to get ahead of the season is by planting winter onions, which are specially bred to withstand cold UK conditions.

By following a month-by-month planting calendar, you can stay on track with sowing, planting, and caring for winter onions — ensuring a healthy, early harvest the following summer. In this guide, we’ll walk through each stage of the process, from preparing soil in autumn to harvesting onions in June and July.

Why Plant Winter Onions?

• Earlier harvest – Ready weeks before spring-planted onions.
• Efficient use of space – Beds stay productive over winter.
• Hardy varieties – Overwintering onions are bred for cold UK weather.
• Beginner-friendly – Simple to plant and maintain.
• Great storage crop – Provides fresh onions well into autumn.

Winter Onion Planting Calendar: Month-by-Month

September – Prepare Soil and Beds

• Clear weeds and debris.
• Dig in well-rotted compost or organic matter.
• Check soil pH (ideal 6.5–7.5). Add lime if too acidic.
• Choose a sunny, well-drained location — raised beds are perfect if you have heavy soil.

October – Plant Autumn Onions (Optional)

• Some overwintering varieties (like Radar and Electric) can be planted in October.
• Planting early gives onions more time to establish before frosts.
• Space sets 10cm apart, rows 25–30cm apart.
• Plant 2–3cm deep with tips just below the soil surface.

November – Main Winter Onion Planting Time

• Best month for planting winter onion sets.
• Choose hardy varieties like Senshyu Yellow or Shakespeare.
• Protect with fleece or netting if birds pull sets up.
• Water only if soil is dry.

December – Final Winter Planting

• Still possible to plant in early December, especially in mild regions.
• Avoid waterlogged beds — onions rot in soggy soil.
• Mulch lightly to protect from frost and suppress weeds.

January – Check Beds and Re-Firm Sets

• Onions remain dormant.
• Check for frost heave — re-firm any sets pushed out of soil.
• Replace fleece or netting if winter storms have damaged covers.

February – Minimal Care Needed

• Still dormant but days are getting longer.
• Check for weeds and remove by hand.
• Avoid feeding yet — wait until growth resumes in spring.

March – Growth Begins

• Onions start growing as temperatures rise.
• Weed regularly — onions dislike competition.
• Apply nitrogen-rich fertiliser (blood meal or poultry pellets) to encourage leafy growth.

April – Encourage Strong Growth

• Water during dry spells.
• Keep weeding to ensure bulbs have space to swell.
• Continue with nitrogen feed if growth is slow.

May – Bulbs Start to Swell

• Switch to potassium-rich feed (e.g., tomato fertiliser) to support bulb development.
• Water consistently in dry weather.
• Stop feeding once leaves begin to yellow.

June – Harvest Time Approaches

• Winter onions are usually ready this month.
• Signs of maturity: leaves yellowing and flopping over.
• Stop watering completely.
• Begin harvesting as bulbs firm up.

July – Main Harvest and Curing

• Lift remaining onions with a fork.
• Cure in a dry, airy place for 2–3 weeks until skins are papery.
• Trim roots and tops or braid onions for storage.
• Store in a cool, dry, well-ventilated space.

Best Varieties for Winter Onion Planting

• Senshyu Yellow – Japanese overwintering onion, very hardy.
• Shakespeare – Reliable and disease-resistant.
• Radar – Popular overwintering variety with good flavour.
• Electric – Attractive red onion suitable for autumn planting.

Protecting Winter Onions

• Birds – Cover beds with fleece or netting until sets root.
• Frost heave – Check after frosts and firm down lifted sets.
• Wet soil – Avoid waterlogged conditions by planting in raised beds.
• Weeds – Remove regularly, as onions struggle with competition.

Harvesting and Storing Winter Onions

• Harvest in June–July once tops have yellowed and flopped.
• Cure for 2–3 weeks before storage.
• Store in mesh bags, nets, or braids in a cool, ventilated space.
• Winter onions keep for 3–5 months.

Common Mistakes with Winter Onions

• Planting too late → Weak root systems and smaller bulbs.
• Planting too shallow → Birds pull sets out easily.
• Waterlogged soil → Leads to rot.
• Overcrowding → Poor air circulation and small bulbs.
• Skipping crop rotation → Increases risk of onion diseases.

Conclusion

Planting winter onions is a simple and effective way to enjoy an early harvest. By following a month-by-month planting calendar, you can prepare your soil, plant at the right time, care for your crop through winter and spring, and enjoy healthy onions by early summer.

For most gardeners, the best time to plant winter onions is November–December, but starting preparations in September and staying on track through to harvest in July ensures strong, reliable crops. With minimal effort, winter onions can keep your garden productive all year long.

Top 10 Questions About Winter Onion Planting

1. When is the best month to plant winter onions?
November–December, with planting possible into January in mild regions.

2. Can I plant winter onions in October?
Yes, though these are often called autumn onions.

3. Do winter onions survive frost?
Yes, overwintering varieties are bred to handle cold UK winters.

4. How deep should I plant onion sets?
2–3cm deep, just below the soil surface.

5. How far apart should I space winter onions?
10cm between sets, 25–30cm between rows.

6. Do winter onions need care in winter?
Very little — just check for frost heave and bird damage.

7. When are winter onions ready to harvest?
Usually June–July.

8. How long do winter onions store?
Around 3–5 months.

9. Can winter onions be grown in containers?
Yes, but use pots at least 25cm deep with free-draining compost.

10. What are the best winter onion varieties?
Senshyu Yellow, Shakespeare, Radar, and Electric.