Onions are a staple crop in most UK gardens, but did you know they’re also one of the best vegetables for companion planting?
When grown alongside the right neighbours, onions can help deter pests, improve flavour, and make more efficient use of your growing space. And when grown inside a polytunnel, these benefits get even better – fewer pests, longer growing seasons, and more control.
Let’s take a closer look at how to companion plant with onions, what works well (and what doesn’t), and how this fits into an ecological approach to growing, like the one adopted by Jamie Walton of Nettles & Petals.
Why Onions Are Great Companion Plants
Onions (and their allium cousins like garlic, shallots, and leeks) naturally repel many common garden pests. Their strong scent is especially effective against aphids, carrot fly, and some beetles. That makes them excellent allies in a more biodiverse planting setup.
In a polytunnel, this pest-deterrent effect is even more useful. You’ve got limited space – so every plant needs to pull its weight. Companion planting allows you to make the most of your beds while keeping your growing system healthy and productive.
Best Companion Plants for Onions
Here are some tried-and-tested companions that thrive alongside onions:
🥕 Carrots
This classic pairing works both ways – onions repel carrot fly, while carrots don’t mind the company. They also grow deeper, so they don’t compete for space with onion roots.
🥬 Lettuce & Leafy Greens
Lettuce has shallow roots and doesn’t take up much space. It grows quickly, so you can interplant it between rows of onions for a harvest while the bulbs mature.
🍓 Strawberries
A surprising but effective pairing – strawberries can benefit from the pest protection onions offer, especially against soil-borne insects.
🌿 Chamomile
Chamomile isn’t just calming in a tea – it’s also thought to improve the flavour and growth of nearby alliums. It attracts beneficial insects too.
🧹 Beetroot & Parsnips
These crops don’t interfere with onions and help fill in beds with similar growing conditions.
🌱 Pro tip: In a polytunnel, companion planting gives you more control over microclimates – so you can fine-tune your layout for airflow, moisture retention, and spacing.
What Not to Plant With Onions
Not every plant gets along with onions. Some can inhibit growth or suffer from stunted development when planted nearby.
❌ Legumes (Beans and Peas)
Alliums tend to suppress nitrogen-fixing bacteria, which legumes depend on. This can reduce bean and pea yields significantly.
❌ Sage and Strong Herbs
Some herbs don’t appreciate onion neighbours – particularly sage, which may struggle to thrive alongside them.
🧠For more on this, see the RHS guidance on growing onions and companion crops.
Companion Planting in a Polytunnel
Polytunnels add another layer of flexibility to companion planting:
- You can sow, plant, and harvest in tighter successions
- Protected cropping reduces pest pressure — but companion planting adds a second layer of defence
- By pairing slower growers like onions with quick crops like salad leaves, you maximise every square metre
Our EasyBuild Polytunnel is designed for exactly this kind of growing – robust enough for year-round planting, with enough height and strength to support trellising, overhead irrigation, or intercropping layouts.
Final Thoughts: Companion Planting as a Growing Philosophy
At its heart, companion planting is about balance and biodiversity – two things we value deeply at Northern Polytunnels. It’s also a principle embraced by growers like Jamie Walton, who are cultivating community spaces built around ecological and inclusive growing.
By thinking beyond the row, and growing crops that support one another, you’re building resilience into your garden – and getting more from your polytunnel.
Ready to Grow More, Naturally?
Whether you’re companion planting for onions or building out a full seasonal plan, our EasyBuild Polytunnels give you the space, strength, and flexibility to do it your way.
👉 Design your tunnel now with our free configurator
