How to Grow Onions in Containers
Growing onions in containers is a brilliant option if you’re short on space, have poor soil, or want more control over growing conditions. With the right container, compost, and care, onions grow just as well in pots as they do in the ground.
⭐ Recommended Products — 🧅 Onions (Seeds, Sets & Storage Essentials)
⭐ Recommended Products — Garden & Allotment Essentials for March
March is when the growing season truly begins. Seeds are being sown daily, beds are prepared and late frosts are still possible — these essentials help produce strong plants and a successful start.
Seed Trays, Modules & Propagation Kits — perfect for tomatoes, brassicas, lettuce, onions and flowers. 👉
Click here to see top options
Heated Propagators, Heat Mats & Grow Lights — improves germination and prevents leggy seedlings during cold nights. 👉
Click here to see top options
Seed & Cutting Compost — essential for healthy seedlings and strong root growth. 👉
Click here to see top options
Garden Fleece & Plant Protection Covers — protects seedlings, potatoes and early plantings from late frost. 👉
Click here to see top options
Spring Vegetable Seeds — carrots, beetroot, peas, spinach and salads can all be started now. 👉
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Garden Kneeler & Seat — makes long sowing and planting sessions far more comfortable. 👉
Click here to see top options
Pressure Washer (Greenhouse & Patio Cleaning) — clean patios, paths and greenhouses before planting. 👉
Click here to see top options
Solar Garden Lights — perfect for enjoying the garden during brighter spring evenings. 👉
Click here to see top options
Onions are a staple crop for gardens and allotments — easy to grow and brilliant for long-term storage when done right.
• Onion Sets (Spring & Autumn Planting)
Small starter bulbs that are quick and reliable to grow — ideal for beginners and perfect for strong, consistent harvests.
👉 Click here to see top options
• Onion Seeds (Wide Variety Selection)
Great if you want more choice, larger crops, or specific varieties for cooking or salads — cost-effective and ideal for early sowing under cover.
👉 Click here to see top options
• Onion & Vegetable Feed (Balanced Fertiliser)
Specially formulated fertiliser to support healthy leaf growth and strong bulb development — apply during the growing season for better yields.
👉 Click here to see top options
• Onion Storage Bags (Breathable Mesh Sacks)
Allows airflow while storing harvested onions — helps prevent rot and keeps bulbs fresh for months.
👉 Click here to see top options
• Onion Drying Rack / Harvest Storage Crate
Perfect for curing onions after lifting — improves longevity and ensures proper drying before storage.
👉 Click here to see top options
This guide explains how to grow onions in containers in the UK, from choosing pots to planting, watering, and harvesting.
Can You Grow Onions Successfully in Containers?
Yes — onions are well suited to container growing.
Container-grown onions:
- Drain better than ground soil
- Warm up faster in spring
- Are easier to protect from pests
- Work well on patios, balconies, and small gardens
They’re also ideal if your garden soil is heavy or waterlogged.
For a full overview of onion growing, see ONION SETS UK: THE COMPLETE GUIDE TO PLANTING, GROWING & HARVESTING ONIONS.
Best Containers for Growing Onions
Onions don’t need deep pots, but they do need space.
Ideal containers:
- At least 20–25 cm deep
- Wide rather than narrow
- With drainage holes
Avoid very small pots, as they dry out too quickly and restrict bulb size.
How Many Onions Per Container?
Spacing still matters in containers.
As a guide:
- Allow one onion per 10–15 cm
- Don’t overcrowd
- Wider spacing gives larger bulbs
For spacing rules, see HOW FAR APART TO PLANT ONION SETS.
Best Compost for Container-Grown Onions
Use:
- Multi-purpose compost
- Free-draining compost
- Avoid heavy garden soil
Adding a little grit or perlite improves drainage and reduces the risk of rot.
Fresh manure should be avoided, as it causes leafy growth rather than bulbs.
When to Plant Onion Sets in Containers
Container-grown onion sets are planted at the same time as ground-grown ones.
- Best time: March
- Earliest: Late February (conditions dependent)
- Latest: April
For full timing advice, see WHEN TO PLANT ONION SETS IN THE UK.
If you’re tempted to plant early, read CAN YOU PLANT ONION SETS IN FEBRUARY first.
How to Plant Onion Sets in Containers
- Fill the container with compost
- Firm lightly but don’t compact
- Push onion sets in so the tip just shows
- Space evenly
- Water gently after planting
Place containers in a sunny, sheltered position.
Watering Onions in Containers
Onions in containers dry out faster than those in the ground.
- Check moisture regularly
- Water when the top compost feels dry
- Avoid waterlogging
Consistent watering is key to bulb size and flavour.
For detailed guidance, see HOW OFTEN SHOULD YOU WATER ONIONS.
Do Container-Grown Onions Need Feeding?
Usually not much.
If compost is fresh:
- No feeding is needed early on
If growth looks weak:
- Use a light, balanced feed once
Overfeeding causes leafy growth and small bulbs.
For feeding advice, see DO ONIONS NEED FEEDING.
Common Problems With Container-Grown Onions
Small Bulbs
Often caused by:
- Overcrowding
- Inconsistent watering
- Poor compost
Bolting
Stress from cold or irregular watering can trigger bolting.
If this happens, see WHY ONIONS BOLT AND HOW TO STOP IT.
When Are Container-Grown Onions Ready to Harvest?
Harvest timing is the same as ground-grown onions.
Onions are ready when:
- Leaves turn yellow
- Tops fall over naturally
For harvest timing, see WHEN ARE ONIONS READY TO HARVEST IN THE UK.
Storing Container-Grown Onions
Container-grown onions store just as well if cured properly.
Follow the same storage steps as ground-grown onions:
- Dry thoroughly
- Store cool and dry
For full guidance, see HOW TO STORE ONIONS LONG TERM.
Summary: Growing Onions in Containers
- Ideal for small spaces and poor soil
- Use wide, well-drained containers
- Space onions correctly
- Water consistently
- Harvest and store the same way as ground onions
For everything else you need to know about growing onions successfully, return to ONION SETS UK: THE COMPLETE GUIDE TO PLANTING, GROWING & HARVESTING ONIONS.
Related Onion Growing Guides
- WHEN TO PLANT ONION SETS IN THE UK
- BEST ONION VARIETIES FOR UK GARDENS
- WHY ONIONS BOLT AND HOW TO STOP IT
- HOW TO GROW ONIONS IN CONTAINERS
- PICKLED RED ONION RECIPE