The short version: Companion planting means growing certain plants together for mutual benefit, and some of it works while a lot of it is folklore. The better supported ideas are flowers that draw in beneficial insects, trap crops that may lure pests away, and tall plants that shelter tender ones. Many specific pairing claims, such as basil improving the flavour of tomatoes, have little evidence behind them, so treat it as one helpful tool, not a guarantee.
Companion planting is one of those gardening ideas that everyone has heard of and few can pin down. Some of it rests on sound biology, and a good deal is passed-down lore that has never really been tested. Most popular advice also comes from the northern hemisphere, so it pays to be a little sceptical and focus on what holds up in an Australian garden.
Does companion planting actually work?
Companion planting works in part, depending on the claim, since a few mechanisms have reasonable support while many plant-by-plant pairings are closer to tradition than science. The trick is telling the two apart before you rearrange the whole patch.
The ideas worth your time share one feature: a clear reason behind them.
- Flowers that feed beneficial insects, so more predators patrol the bed.
- Trap crops that draw pests away from your vegetables.
- Legumes that can enrich the soil for the next crop.
- Tall plants that shade or physically support shorter ones.
The weaker claims tend to be the very specific ones, and Australian sources are honest about this. Sustainable Gardening Australia notes there is only limited scientific information on the subject, and that some combinations work while others are hit and miss.
Flowers that bring in the good bugs
One of the more reliable payoffs can be planting flowers that attract beneficial insects, which is among the better supported parts of companion planting.
Small, open flowers help support hoverflies, ladybirds, lacewings and parasitic wasps. The adults feed on nectar and pollen, and many of their young prey on aphids and caterpillars. Sweet alyssum, calendula, cosmos, dill and coriander all do this job well, and a packet of mixed flower seeds along a bed edge is an easy start.
Keep something in flower across as much of the year as you can. A bed edge humming with bees on a warm morning is a good sign the balance is tipping your way, so aim for variety and continuous flowering rather than one big flush, tucking a few seedlings in by the fence where there is room.
Trap crops and living supports
Some companions work by sacrificing themselves or by lending a hand physically, which are simple practical effects rather than chemistry.
Nasturtiums are a classic trap crop. Aphids and cabbage white butterfly (Pieris rapae) often go for them first, drawing pressure away from your vegetables. The catch is that you have to remove or squash the pests on the trap plant, or you are simply running a very pretty aphid nursery by the back path.
Tall plants can also earn their place. Climbing beans can scramble up a sturdy stand of corn, and a row of taller crops can throw afternoon shade over lettuce through the worst of the summer heat. You notice the win on a hot afternoon, when the salad leaves are still crisp.
What the old companion charts get wrong
Plenty of well-known pairings simply do not hold up, so take the famous charts with a grain of salt. "Carrots love tomatoes" comes from the title of a 1975 book, not from data. The idea that basil improves the flavour of a tomato is also not supported, since plants do not absorb flavour from their neighbours.
Marigolds are a more interesting case. French marigolds can help suppress root-knot nematodes (Meloidogyne species), but only when grown thickly and dug in over much of a season. The effect also varies with the type of marigold and the nematode species, and a few plants dotted among the tomatoes are unlikely to shift soil nematodes. They still earn a spot in the bed, because they draw in beneficial insects.
Peas, beans and the nitrogen question
Legumes such as peas and beans can add nitrogen to the soil, but not in the way many gardeners think. The benefit goes mostly to the next crop, not the plant alongside.
Peas and beans host helpful bacteria in nodules on their roots. When the right bacteria are present, they draw nitrogen from the air and hold it in a form plants can use. That nitrogen becomes available as the roots break down, which suits whatever you plant next.
So when a pea or bean crop finishes, do not yank it out. Cut the plants off at the base with secateurs and leave the roots in the ground. The honest caveat is that the home-garden gain is usually modest, since much of the nitrogen leaves in the pods you pick for dinner.
Companion planting across Australia's climate zones
Timing and plant choice shift a great deal across the country, so local conditions matter more than any chart. What flowers in July in Cairns is very different from what flowers in Hobart.
In tropical and subtropical gardens, from Darwin to Brisbane, the warm, humid months can bring heavy insect pressure, so a long flowering season often helps. In temperate areas such as Sydney and Melbourne, the four seasons give clear windows for crops.
In mediterranean zones, the mild wet winters and dry summers favour winter and spring flowering. This includes Perth and southern Western Australia, along with the Adelaide region and similar dry-summer parts of South Australia. In arid, cool and alpine areas, from Alice Springs to Canberra and the southern tablelands, the window is shorter, so lean on hardy flowers and quick-maturing varieties.
Frequently asked questions
Does companion planting really work?
Partly. Some ideas have decent support, such as flowers that attract beneficial insects, trap crops, and legumes feeding later crops. Many specific pairing claims have little evidence, and much of the lore comes from the northern hemisphere, so it transfers imperfectly here.
Does basil make tomatoes taste better?
There is no reliable evidence that it does, and flavour does not transfer between living plants. Basil and tomatoes still grow happily side by side, so plant them together for convenience, not for taste.
Which flowers attract beneficial insects?
Sweet alyssum, calendula, cosmos, dill and coriander can all attract them. Their small, open flowers feed hoverflies, ladybirds, lacewings and parasitic wasps. Aim for a mix and continuous flowering through the seasons.
Do marigolds repel pests?
Not broadly. French marigolds can help reduce root-knot nematodes in the soil, but mainly when grown densely and dug in over a season. Results vary, and a few scattered plants are unlikely to repel most pests, though they do help by attracting beneficial insects.
Do peas and beans feed the plants growing next to them?
Not while they are alive. Legumes fix nitrogen in their roots, and it mostly becomes available to the following crop as the roots break down. Leave the roots in when the crop finishes.
Can companion planting stop Queensland fruit fly?
No. Queensland fruit fly (Bactrocera tryoni) is a serious pest of fruiting crops, and companion plants will not control it. Use proven methods such as netting, baiting and good garden hygiene instead.
Companion planting is at its best treated as gentle encouragement rather than a rulebook. Feed the soil, plant a good mix of flowers, and let the beneficial insects do their quiet work. For more on drawing those helpers in, see our guide to a beneficial bug mix for Australian gardens.
Related growing guides
- Flowers in the vegetable garden for bees
- Organic pest control in Australia
- The most nutritious things to grow at home
Ready to plant? Browse our Vegetable Seeds.