Let Nature Do the Work: Companion Planting for Natural Pest Control

Why inviting the right plants — and the right insects — into your garden is the smartest pest management you'll ever do

This morning I found a ladybird on one of my geraniums. Not just one, as it turned out — there were three, tucked among the blooms, going quietly about their business. To anyone passing by, it might have looked like nothing much. To me, it was a reminder of exactly why I garden the way I do.

That cluster of ladybirds represents nature's pest control at its finest. A single ladybird will eat up to 5,000 aphids over the course of its lifetime. No sprays, no chemicals, no intervention from me — just a garden designed to welcome them in.

Companion planting is one of the oldest techniques in horticulture, and after decades of growing vegetables and flowers together, I am more convinced of its value than ever. Here's what I've learned.

What Is Companion Planting, Really?

At its simplest, companion planting means growing different plants in close proximity so that they benefit one another. Those benefits can take many forms — deterring pests, attracting beneficial insects, improving soil, or providing physical shelter.

It is not magic, and I won't pretend every pairing works every time. Gardens are complex ecosystems and results vary. But used thoughtfully, companion planting meaningfully reduces pest pressure and helps create a garden that largely looks after itself.

The Insects You Want to Attract

Before choosing your companion plants, it helps to know which beneficial insects you're trying to encourage and what they need.

The key takeaway from this table is that most beneficial insects need flowers — specifically open, accessible flowers where they can reach the nectar and pollen. A vegetable garden that contains no flowers is a garden that struggles to sustain a healthy predator population.

EXPERT TIP
Geraniums — particularly the variety Geranium sanguineum — are exceptional at attracting ladybirds, as I was reminded this very morning. They also attract hoverflies and lacewings. Dotting hardy geraniums through and around the kitchen garden costs almost nothing and pays dividends all summer long.

The Best Companion Planting Combinations

Here are the pairings I return to year after year, with consistent results:

Tomatoes + Basil: One of the most famous combinations, and one that genuinely earns its reputation. Basil is believed to repel aphids and whitefly, and the aromatic oils may confuse pests searching for their host plant. I grow basil in pots between my tomato grow-bags so I can move them as needed.

Brassicas + Nasturtiums: Nasturtiums act as a sacrificial trap crop — aphids, particularly the black bean aphid, are strongly attracted to them and will colonise nasturtiums in preference to your kale or Brussels sprouts. Once the nasturtiums are covered in aphids, they in turn attract ladybirds, lacewings and hoverflies. It is a beautifully self-managing system.

Carrots + Onions (or Chives): The classic pairing for mutual protection. Carrot fly is deterred by the strong scent of alliums, while onion fly finds carrots similarly confusing. Growing them in alternating rows creates an olfactory barrier for both pests.

Beans + Summer Savory: Summer savory has a long folk history as a bean companion, said to deter black bean aphid and improve the flavour of the crop. I find the aphid deterrence genuine — beds with savory nearby consistently show lower aphid pressure.

Brassicas + Poached Egg Plant (Limnanthes): This low-growing annual is one of my favourite companion plants full stop. It flowers prolifically from June onward, is irresistible to hoverflies, and self-seeds reliably so it comes back year after year with no effort on your part.

EXPERT TIP
Don't limit companions to the vegetable beds. Planting flowering herbs — fennel, dill, coriander allowed to bolt, chives — in borders adjacent to your kitchen garden creates a reservoir of beneficial insects that move freely between the ornamental and edible areas.

Plants That Deter Pests Directly

Some companions work not by attracting predators but by actively putting pests off:

• Marigolds (Tagetes) — French marigolds in particular release a root exudate that suppresses soil nematodes, and the scent is said to confuse aphids and whitefly. Grow them densely around tomatoes and peppers.
• Lavender — A strong deterrent for aphids and ants (ants farm aphids, so deterring ants matters). Also attractive to bumblebees which aid pollination.
• Rosemary — The volatile oils deter a range of insects including cabbage moth. Grow as a low hedge around brassica beds where practical.
• Alliums (including ornamental) — Allium bulbs planted through beds deter a wide range of pests and their flowers are excellent for pollinators in early summer.
• Mint — Highly effective against aphids and flea beetle. Must be grown in containers or it will take over. I sink a pot of mint into the soil beside brassicas.

A Simple Companion Planting Plan for a Raised Bed

If you're new to this and want a practical starting point, here is a planting framework for a standard 1.2m x 2.4m raised bed growing mixed vegetables:

1. Sow or plant your main vegetable crop as normal
2. Add a row of French marigolds along the sunniest edge
3. Plant one clump of basil or chives at each corner
4. Allow one or two nasturtiums to trail along the front edge
5. Set a pot of mint into the soil at one end
6. Leave a small patch — even 30cm square — for poached egg plant or phacelia to flower freely

That is genuinely all it takes to begin. You do not need to redesign your entire garden. Start with one bed, observe what visits over the course of the summer, and build from there.

What To Avoid

Companion planting has its limits, and some combinations actively cause problems:

• Do not grow fennel near most vegetables — it is allelopathic and inhibits the growth of many crops. Keep it in its own spot at the garden's edge where it can still attract beneficial insects.
• Avoid planting members of the same family too close together as companions — it concentrates rather than confuses pests.
• Be cautious with strong allelopathic plants like wormwood (Artemisia) near tender crops — the chemical compounds can suppress growth.

Patience and Observation

Companion planting rewards the attentive gardener. Keep a simple notebook through the season — note which plants seem to attract the most beneficials, where you find pest hotspots, and which combinations appear to reduce damage. Over two or three seasons you will build up a detailed picture of what works in your specific garden, in your specific conditions.

No book or blog — including this one — can replicate that knowledge. Your garden will teach you, if you take the time to watch.

Those three ladybirds this morning were not an accident. They were there because over the years I have planted to welcome them. That, in the end, is what companion planting is really about — not controlling your garden, but making it a place where nature wants to be.