Getting Onions Started: When to Plant Onions – Kings Seeds
Getting Onions Started: When to Plant Onions
Growing onions from seed, can be easy, cost-effective and oh so satisfying. For New Zealand gardeners, knowing when to plant onions NZ style makes all the difference between thin shoots and full, large bulbs. At Kings Seeds, a trusted name among seed suppliers NZ, we believe growing your own should feel simple, achievable, and rewarding. Whether you’re searching for the best seeds NZ, planning your next garden season, or looking to buy seeds NZ with confidence, this guide will walk you through every step of growing onions NZ with ease. Watch our Onion Top Tips here.
Different Onion Varieties
Choosing the right onion variety sets the tone for your whole season. Each type behaves a little differently depending on daylight hours and temperature across Aotearoa.
Main types to consider:
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Brown onions
Reliable, long-lasting, and perfect for everyday cooking. These are your pantry staples. Varieties such as Pukekohe Long Keeper, Yellow Sweet Spanish, Italian Long Keeper, and Organic Ailsa Craig.
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Red onions
Sweeter with a milder bite. If you’re wondering about growing red onions, they thrive in similar conditions but often need a little more patience. Varieties such as Red Brunswick, Red Amposta, and Purplette.
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White onions
Crisp and sharp, ideal for fresh use. Varieties such as White Sweet Spanish and Pearl Drop.
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Spring onions
Fast-growing and perfect for small spaces or pots. Great if you’re learning how to grow spring onions for quick harvests. Varieties such as Tokyo Long White, Ishikura, and Red bunching.
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Day-length varieties
Short-day types suit warmer northern regions.
Long-day types perform better in cooler southern climates. Varieties such as Red Brunswick and Ailsa Craig.
Sowing & Growing Times for Different Onion Types
Timing matters more than most people realise. Onions rely on daylight length to trigger bulb formation, so getting your sowing window right is key.
General guide for New Zealand:
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When to sow onion seeds NZ
Late summer to early autumn (February to April) works best in most regions.
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When to plant onion seeds NZ (seedlings out)
Transplant young seedlings in late autumn to early winter once they are pencil-thick.
For those asking when to plant red onions NZ, the same timing applies, though some red varieties may prefer slightly warmer soil to get started.
Growth timeline:
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Seed to transplant: 8–10 weeks
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Transplant to harvest: 4–6 months
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Total time: roughly 5–7 months, depending on variety
If you’ve ever wondered how long does an onion take to grow, that’s your window.
How to Sow Onion Seeds (Tips for Strong Germination)
Starting from seed gives you more choice and better value.
Step-by-step approach:
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Use a fine, well-draining seed mix, loose soil helps roots develop freely.
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Sow thinly in trays or rows, seeds are small, so avoid crowding.
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Cover lightly, a gentle dusting of soil is enough.
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Keep moisture consistent, not soaking, not dry. Think of it like a wrung-out sponge.
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Place in a warm, bright spot, germination usually takes 7–14 days.
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Thin early, give each seedling space to grow strong.
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Harden off before planting out, gradually introduce outdoor conditions.
A helpful tip for beginners learning how to grow onions in a pot: choose a deep container, at least 20 cm, with excellent drainage.
When to Sow vs When to Plant Onions
This is where many gardeners trip up, so let’s keep it simple.
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Sowing means starting seeds in trays or beds
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Planting means moving (transplanting) established seedlings into their final position
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Most onions prefer direct sowing. Which means planting seeds directly where they will grow to full maturity. Skipping the transplanting step entirely.
Key timing difference between sowing and transplanting:
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Sow seeds in late summer or early autumn
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Transplant seedlings out in late autumn or early winter
Waiting until seedlings are sturdy helps them handle cooler weather. If planted too early, they may struggle. Too late, and bulbs won’t size up properly.
For those exploring planting red onions NZ, the same rhythm applies, just keep an eye on soil warmth.
Growing Onions Successfully in New Zealand
Once your seedlings are in the ground, the real magic begins.
Soil and position
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Full sun is essential
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Free-draining soil prevents rot
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Add compost before planting for steady nutrients
Spacing
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10–15 cm between plants
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25–30 cm between rows
Crowding leads to smaller bulbs, so give them breathing room.
Watering
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Regular moisture during early growth
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Reduce watering as bulbs mature
Too much water late in the season can affect storage quality.
Feeding
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Use a balanced fertiliser early on
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Avoid high nitrogen later, as it encourages leaf growth over bulbs
Companion Planting with Onions
Onions can support other plants while also benefiting from good neighbours.
Great companions:
Many gardeners explore onions and tomatoes companion planting, which can work well. Tomatoes benefit from the natural pest-deterring qualities onions provide.
What should you not plant with onions?
These crops don’t get along with onions and may struggle nearby.
If you’re wondering what to plant near onions, stick with leafy greens and root crops for best results.
Growing Onions in Raised Beds and Small Spaces
Not everyone has a sprawling backyard, and that’s perfectly fine, onions can be grown in raised beds, containers and pots also.
How to grow onions in raised beds:
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Ensure good drainage
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Maintain consistent spacing
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Avoid overcrowding
How to grow onions in a pot:
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Choose a wide, deep container
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Use quality potting mix
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Water regularly but lightly
Spring onions are especially forgiving here, making them ideal for beginners.
Harvesting and Storing Onions
The final stage is where patience pays off.
When to harvest onions:
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Tops begin to yellow and fall over
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Bulbs feel firm and well-formed
Gently lift them from the soil and allow them to dry in a warm, airy place.
Curing process:
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Lay bulbs out for 1–2 weeks
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Keep skins dry and intact
How to store red onions and brown onions:
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Store in a cool, dry place
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Use mesh bags or baskets for airflow
Pro storage tip: Keep stored onions away from apples and pototoes as the gases released from these promotes onions to sprout.
What to Plant After Onions
If you’re thinking about what to plant after onions, choose crops that benefit from the cleared space and remaining nutrients. Once your onions are harvested, the soil is ready for a fresh chapter.
Great follow-up crops:
Onion F.A.Q
Can you grow onions in winter in NZ?
Yes, onions grow well through winter when planted in autumn. Cooler temperatures support steady development without stressing the plants.
Can I leave onions in the ground all winter?
You can, provided soil drains well. Wet conditions increase the risk of rot, so avoid heavy, waterlogged areas.
Which is the best month to sow onion seeds?
February to April works best across most regions. This timing aligns with natural daylight changes needed for bulb formation.
How do I get my onions to bulb up?
Correct timing, proper spacing, and enough sunlight are key. Bulbs form when daylight hours reach the right length for the variety.
How do I store my onions?
Dry them thoroughly after harvest, then store in a cool, ventilated spot. Avoid sealed containers to prevent moisture build-up.
Ready for Your Next Garden Chapter?
Once your onions are lifted, cured, and tucked away, there’s something deeply satisfying about knowing your pantry started as a handful of seeds. That’s the beauty of growing your own, simple beginnings that turn into something real, useful, and nourishing.
If you’re feeling inspired to get started, explore the Kings Seeds range and find the right varieties for your garden. With one of the widest selections of seeds NZ, you’ll find everything you need to grow with confidence.
