Onions in December: Tips and Advice for Planting and Growing Onions During Winter

As the chill of December sets in and gardens across the country start to slow down for winter, the seasoned gardener knows that there’s still work to be done. One vegetable that can thrive in the colder months is the humble onion. Whether you’re growing onions for a spring harvest or want to get ahead for next year’s garden, December is an excellent time to start preparing and planting certain varieties of onions.

In this article, we’ll cover everything you need to know about growing onions in December, including tips and advice on soil preparation, seed sowing, and how to care for onions during winter. By the time spring rolls around, you’ll have strong, healthy onions well on their way to harvest.

Why Plant Onions in December?

December is typically seen as a quiet month in the garden, but that doesn’t mean it’s time to stop planting. In fact, onions are an ideal crop for this time of year because they are hardy and can tolerate cooler temperatures. While many crops won’t survive winter frosts, onions can develop strong roots throughout the colder months, preparing them for vigorous growth in the spring.

By planting onions in December, you give them a head start, allowing them to grow steadily through winter. This early planting can lead to larger bulbs and an earlier harvest compared to spring-planted onions.

The Benefits of Planting Onions in December:

Cold Tolerance: Certain varieties of onions are well-suited to winter growing and can withstand cold, even frost.
Strong Root Development: Planting early allows onions to establish strong root systems, making them more resilient.
Earlier Harvest: Onions planted in December can often be harvested earlier than those planted in spring, giving you a jumpstart on your summer gardening.
Free Up Space: By getting onions out of the way early, you free up valuable garden space in spring for other crops.

Choosing the Right Onion Varieties for December Planting

Not all onions are suitable for winter planting, so it’s important to choose varieties that thrive in cooler temperatures. There are two main options when planting onions in December: onion sets or seeds.

Onion Sets

Onion sets are small, immature onions that can be planted directly into the ground. They are easier to plant and faster to mature than seeds, making them a great option for winter growing. Sets are typically hardier than seeds and more resistant to cold weather.

Popular onion set varieties for December include:

Electric Red: A beautiful red onion that is well-suited to winter planting and produces mild, sweet bulbs.
Senshyu Yellow: A reliable and cold-hardy variety that thrives in winter and produces large, round onions.
Radar: A traditional winter onion variety known for its hardiness and strong flavor.

Onion Seeds

If you prefer growing onions from seed, December is still a great time to start sowing indoors. Onions from seed will take longer to mature than sets, but they can produce stronger plants and larger bulbs in the long run.

Good onion seed varieties for winter sowing include:

Alisa Craig: Known for producing large bulbs, Alisa Craig is a favorite for overwintering and performs well when started in December.
Ailsa Craig: Another large variety that is ideal for winter sowing and gives great results come harvest time.

When starting onions from seed, it’s best to sow them in seed trays indoors, where you can control the temperature and ensure they get a strong start before transplanting them outdoors in early spring.

Preparing the Soil for Winter Onion Planting

One of the most important steps in growing onions in December is preparing the soil. Onions thrive in loose, well-drained soil that is rich in nutrients. Because onions planted in winter will be in the ground for several months, it’s essential to get the soil right from the start.

Steps for Preparing the Soil:

Clear the Area: If you haven’t already done so, remove any debris, old crops, or weeds from the area where you plan to plant your onions.
Amend the Soil: Onions prefer slightly acidic to neutral soil with a pH between 6.0 and 7.0. Before planting, amend the soil with well-rotted compost or organic matter to improve drainage and boost nutrients.
Improve Drainage: In winter, poor drainage can lead to waterlogged soil, which can cause onions to rot. If your garden soil tends to retain water, consider planting onions in raised beds or adding sand or grit to improve drainage.
Fertilize: Onions are heavy feeders and require plenty of nutrients to grow strong. Add a balanced fertilizer high in phosphorus to encourage root growth before planting.

How to Plant Onions in December

Once your soil is prepared, it’s time to plant your onion sets or seeds. Here’s a step-by-step guide to ensure success:

Planting Onion Sets

Spacing: Plant your onion sets about 10-15cm (4-6 inches) apart, with 30cm (12 inches) between rows. This spacing allows enough room for the bulbs to grow.
Depth: Gently push the onion sets into the soil, pointed end up, so that the top of the set is just below the soil surface (about 2.5cm or 1 inch deep).
Watering: Water the sets immediately after planting to help them settle into the soil. Keep the soil moist but not waterlogged throughout the winter.

Sowing Onion Seeds Indoors

Seed Trays: Fill seed trays with seed compost, and sow the onion seeds about 1cm (½ inch) deep.
Germination: Place the trays in a warm spot, such as on a sunny windowsill or in a greenhouse, and keep the soil moist. Onion seeds typically take 10-14 days to germinate.
Transplanting: Once the seedlings are large enough to handle, transplant them into larger pots or directly into the garden in early spring, spacing them the same as onion sets.

Caring for Onions Through Winter

Winter onions require minimal care, but there are a few key things to keep in mind to ensure they grow well throughout the colder months.

Watering

Onions need consistent moisture, but in winter, overwatering can lead to rot. Monitor the soil and only water when it becomes dry to the touch. If you live in an area with heavy winter rainfall, make sure your soil is well-draining to avoid waterlogging.

Mulching

To protect your onions from extreme cold and fluctuating temperatures, consider adding a layer of mulch around the plants. Mulching with straw or compost helps insulate the soil, keeping it warmer during frosty periods.

Frost Protection

While onions are hardy and can tolerate frost, severe cold snaps can still damage young plants. If you’re expecting extreme frost, you can cover your onions with garden fleece or cloches for added protection.

Pests and Diseases

Onions are generally low-maintenance and suffer from few pests during winter. However, be on the lookout for common issues such as:

Onion fly: These pests lay eggs near the base of onion plants. If the larvae hatch, they can cause damage to the roots. Use fine mesh netting to protect your onions from onion flies.
White rot: A fungal disease that thrives in cool, wet conditions. Prevent white rot by planting onions in well-draining soil and rotating crops to avoid planting onions in the same spot each year.

Harvesting Winter Onions

Onions planted in December will be ready for harvest by early to mid-summer, depending on the variety. You’ll know they’re ready when the tops of the plants start to yellow and fall over. At this point, stop watering and allow the onions to dry in the soil for a few days before harvesting.

Once harvested, onions should be left to dry in a warm, well-ventilated area for a week or two. Properly cured onions can be stored for several months in a cool, dry place.

Conclusion

Planting onions in December is a great way to get a head start on your gardening season. By choosing hardy varieties, preparing the soil properly, and providing the right care through winter, you’ll be rewarded with a bountiful harvest come summer. Onions are a resilient and rewarding crop, perfect for gardeners looking to make the most of their winter growing season.

Whether you’re using onion sets or seeds, follow the tips in this guide to ensure your onions grow strong and healthy, and you’ll enjoy delicious homegrown onions all year round.

Find out more things you can grow in December here