Onion Sets UK: A Guide to Planting and Growing Onions from Sets
Onions are one of the most essential vegetables in any kitchen, and growing them from onion sets is the easiest way to achieve a high-yield, low-maintenance crop in your garden.
If you’re wondering how to grow onions from sets in the UK, this guide will cover everything you need to know—from choosing the best onion sets to harvesting and storing your onions.
Whether you’re a beginner or an experienced gardener, onion sets are the simplest way to grow flavourful, homegrown onions with minimal effort!
What Are Onion Sets?
Onion sets are small, immature onion bulbs that have been grown from seed and partially matured, then stored for planting the following season.
✔️ Faster growth than seeds
✔️ More resistant to disease
✔️ Less maintenance required
Using onion sets eliminates the need for delicate seed sowing, making them the best option for UK gardeners looking for an easy onion-growing method.
Best Onion Sets for UK Gardens
There are several types of onion sets, each with different characteristics. Here are some of the best varieties for UK growing conditions:
🧅 White & Yellow Onion Sets (Best for Cooking)
- Sturon: A popular variety producing medium to large golden onions with a mild, sweet flavour.
- Centurion: Early maturing, great for long-term storage.
- Radar: A hardy, overwintering variety ideal for planting in autumn.
🟣 Red Onion Sets (Best for Salads & Roasting)
- Red Baron: A classic, deep red onion with a sweet, crisp texture.
- Electric Red: Ideal for overwintering, producing mild and juicy onions.
🌱 Shallot & Specialty Sets (Best for Flavour)
- Golden Gourmet Shallots: Great for pickling and roasting.
- Echalote Grise: A traditional French shallot known for its intense flavour.
Tip: Choose heat-treated onion sets to reduce the risk of bolting (going to seed early).
When to Plant Onion Sets in the UK
The best time to plant onion sets in the UK depends on the variety:
| Planting Season | Best Varieties | Planting Months | Harvest Time |
|---|---|---|---|
| Spring Planting | Sturon, Centurion, Red Baron | March – April | July – August |
| Autumn Planting (Overwintering) | Radar, Electric Red | September – November | June – July |
🔹 Spring-planted onions grow quickly and are ready by mid-summer.
🔹 Autumn-planted onions mature slowly over winter and are ready for an early summer harvest.
Tip: If you live in a colder part of the UK, plant in March-April to avoid frost damage.
How to Plant Onion Sets in the UK
Growing onions from sets is simple, but proper planting ensures strong, healthy growth.
🌿 Step 1: Choose the Right Location
✔️ Full sun (at least 6 hours per day)
✔️ Well-draining soil, rich in organic matter
✔️ Avoid planting onions in heavy clay soils
🌱 Step 2: Prepare the Soil
1️⃣ Remove weeds and rake the soil to a fine texture.
2️⃣ Add organic compost or well-rotted manure for nutrients.
3️⃣ Avoid fresh manure, as it can cause onions to rot.
🧅 Step 3: Planting the Onion Sets
1️⃣ Space onion sets 10-15cm (4-6 inches) apart in rows.
2️⃣ Rows should be 30cm (12 inches) apart for good airflow.
3️⃣ Push each onion set into the soil so just the tip is visible.
4️⃣ Firm the soil around the bulbs and water lightly.
Tip: Don’t plant onion sets too deep—just below the surface is perfect!
Caring for Onion Sets
Once planted, onions need minimal maintenance, but these steps will ensure a healthy crop.
💧 Watering Onions
- Water regularly during dry spells, but avoid overwatering.
- Stop watering 2-3 weeks before harvest to allow onions to dry properly.
🌱 Mulching & Weed Control
- Onions dislike competition, so keep the area weed-free.
- Use mulch (straw or compost) to retain moisture and suppress weeds.
🌼 Preventing Bolting (Going to Seed Too Early)
- Choose heat-treated onion sets to reduce bolting risk.
- Water consistently—stress from dry periods can trigger early flowering.
Fact: Onions don’t need much feeding. Too much nitrogen can reduce bulb formation!
Common Onion Pests & Diseases (And How to Prevent Them!)
🪰 Onion Fly – Larvae burrow into onion bulbs, causing rot.
✅ Prevent by using fine mesh netting over young plants.
🦠 White Rot – Fungal disease causing yellow leaves and rotting roots.
✅ Avoid planting onions in the same spot every year (crop rotation).
🐛 Thrips – Tiny insects that damage onion leaves.
✅ Spray with soapy water or use natural predators like ladybirds.
Tip: Growing carrots near onions helps repel onion flies and carrot root flies!
When & How to Harvest Onions
🌿 When to Harvest
Onions are ready to harvest when:
✔️ The leaves turn yellow and fall over.
✔️ The bulbs have fully formed and are firm.
| Onion Type | Harvest Time |
|---|---|
| Spring-planted onions | July – August |
| Autumn-planted onions | June – July |
🧅 How to Harvest & Store Onions
1️⃣ Gently lift onions from the soil using a fork.
2️⃣ Leave them to dry in the sun for 1-2 weeks to cure.
3️⃣ Store in a cool, dry place (like a shed or garage).
✅ Properly stored onions last 4-6 months!
Tip: Store onions in mesh bags or hanging nets for the best airflow.
Frequently Asked Questions (FAQs)
What’s the difference between onion sets and onion seeds?
Onion sets are partially grown bulbs, while onion seeds take longer to develop. Sets are easier to grow and more reliable.
Do onions grow back after harvesting?
No, onions are harvested once per season, but spring onions can regrow if left in the ground.
Can I plant supermarket onions?
You can try, but supermarket onions are not treated for growing, and may bolt early or fail to produce large bulbs.
How many onions will one set grow?
Each onion set grows one onion bulb. For shallots, each set can produce multiple bulbs.
Can I grow onions in pots?
Yes! Use a deep container (at least 20cm deep) and ensure good drainage.
Final Thoughts: Start Growing Onions from Sets Today!
Growing onions from sets in the UK is easy, rewarding, and requires minimal effort.
✔️ Choose spring or autumn onion sets based on your planting season.
✔️ Plant in well-drained, sunny locations for best results.
✔️ Keep soil weed-free, water moderately, and harvest when leaves fall over.
Ready to grow your own onions? Grab your onion sets and start planting today! 🌱🧅