Companion planting in Australian gardens: what grows well together

Companion planting is the practice of growing certain vegetables, herbs and flowers together because they help each other - by deterring pests, attracting pollinators, fixing nitrogen, providing shade, or simply not competing for the same nutrients. In Australian gardens the most reliable pairings are tomatoes with basil, carrots with onions, corn with beans and pumpkin, and brassicas with dill or marigolds. The least reliable is anything that sounds magical and lacks a sensible mechanism - most "tomatoes hate cucumbers" folklore is just folklore.

Used well, companion planting raises yields and reduces spraying. Used badly, it's a memory test that distracts from the basics.

What is companion planting, really?

Companion planting is just plant-spacing with a purpose. There are four mechanisms that actually work in Australian backyards:

1. Pest masking and trap-cropping. Strong-smelling herbs confuse insect pests that find their hosts by scent. Nasturtiums lure aphids away from beans.
2. Beneficial insect habitat. Flowering herbs (alyssum, dill, coriander gone to flower) feed the hoverflies, lacewings and parasitic wasps that eat your aphids and caterpillars.
3. Nitrogen fixing. Legumes (beans, peas, broad beans) host bacteria in their roots that turn atmospheric nitrogen into plant food. Crops planted after legumes get a free feed.
4. Physical structure. Tall plants shade tender crops in summer. Climbing beans use corn as a living trellis. Sprawling pumpkin shades soil and suppresses weeds.

If a pairing doesn't fit one of these mechanisms, treat the claim with scepticism.

Ten companion plantings that work in Australia

1. Tomatoes + basil

Basil's volatile oils repel some thrips and whitefly, and the two crops want the same conditions: full sun, regular water, warm soil. Plant basil at the base of each tomato. Bonus: when basil flowers, hoverflies arrive to police your aphids.

2. Carrots + onions (or chives, or leeks)

The classic pairing. Carrot fly is rare in Australia but the broader principle holds - onion-family scent masks carrot foliage from pests, and the two crops have completely different root depths so they don't compete.

3. Corn + climbing beans + pumpkin ("Three Sisters")

A complete polyculture. Corn grows tall, beans climb the corn and fix nitrogen, pumpkin sprawls below and shades the soil. Works brilliantly in subtropical and temperate Australia. Plant corn first, beans two weeks later, pumpkin around the edges.

4. Brassicas + dill, coriander or marigolds

Cabbage white butterfly is the worst pest in an Australian winter brassica patch. Marigolds (Tagetes) and flowering dill attract parasitic wasps that lay eggs in cabbage white caterpillars. Plant 3–5 marigolds per square metre of brassicas.

5. Lettuce under taller crops

Lettuce bolts (goes to seed) in heat. Plant it between tomato cages or beneath staked beans for summer shade - you'll keep harvesting leaves weeks longer than lettuce in full sun.

6. Strawberries + borage

Borage is a magnet for native bees and improves strawberry fruit set. Its flowers are also edible (sweet, cucumber-flavoured) and the leaves can be chopped as mulch.

7. Capsicum + basil + parsley

Same temperature and water needs as tomatoes. Basil keeps pests away, parsley flowers (in its second year) feed predatory insects.

8. Cucumbers + nasturtiums + dill

Nasturtiums trap aphids and cucumber beetle. Dill, allowed to flower, supports beneficial wasps. The combination meaningfully reduces summer pest pressure on cucurbits.

9. Broad beans + spinach or silverbeet

Broad beans fix nitrogen as they grow. Spinach and silverbeet, planted alongside, get the benefit without needing the beans to be dug in. After the beans finish, chop the foliage back into the bed.

10. Beetroot + bush beans + onion

Beetroot doesn't mind a little crowding, bush beans add nitrogen, and onions keep insects out. A productive trio for a single square metre.

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What NOT to plant together

A short list of pairings that genuinely cause problems:

• Fennel with anything. Fennel suppresses the growth of most surrounding plants. Plant it in its own corner.
• Allium family (onion, garlic, chives) with peas and beans. Onions slow legume growth. Keep a path between them.
• Brassicas with strawberries. Brassicas are hungry and outcompete strawberries; the two also share some root pests.
• Tomatoes with corn. Both attract corn earworm / tomato fruitworm. Combine them and you concentrate the pest.
• Potatoes with tomatoes. Same family, same diseases. Late blight will jump between them.
• Cucumbers with sage. Sage's strong oils stunt cucumbers. Keep your sage with the rosemary and thyme.

Most other "incompatible" pairings you see in old garden books have little evidence behind them. Don't lose sleep over them.

Does companion planting really work in Australia?

Yes - but treat the results as moderate, not magical. In trials, well-designed polyculture beds show:

• 20–40% fewer pest outbreaks than monoculture beds
• 10–20% higher total yield per square metre, because the bed is better packed
• Significantly more beneficial insects on flowering herbs

You'll never get a pest-free garden from marigolds alone. Companion planting works alongside healthy soil, the right planting time, and a watchful eye.

Australian companion planting FAQ

Do marigolds actually work? Yes, for some pests - particularly nematodes (Tagetes patula has been shown to suppress root-knot nematodes in soil), and they reliably attract beneficial insects when in flower. They're not a force field.

Should I plant flowers in my vegetable garden? Always. Aim for at least 10% of bed area in flowering herbs or annual flowers. Alyssum, calendula, borage, dill and coriander allowed to flower are the highest-value choices.

Can I plant tomatoes near cucumbers? Yes. They're not antagonistic. Both like warmth, sun and regular water. Keep cucumbers on a trellis so they don't smother the tomato.

Is companion planting a replacement for crop rotation? No. Even in a perfectly companion-planted bed, you still need to rotate plant families year to year to avoid soil-borne disease.

What's the easiest companion combination to start with? Tomatoes, basil and marigolds in one bed. Three plants, three different functions, dead easy to set up.

Do I need a separate herb garden? No - and you probably shouldn't have one. Herbs do more work scattered through the vegetable beds than clustered together.