Some plants are better neighbours than others. Companion planting is the ancient practice of growing plants together for mutual benefit. One plant repels the pests that plague another. One fixes nitrogen in the soil that another needs. One provides shade for a plant that's burning in the heat. It's not magic — it's ecology, and it works. Here are proven companion planting combinations for Australian gardens.
How companion planting works
Companion planting relies on three main mechanisms:
Pest and disease deterrence: Some plants (like basil and marigolds) repel pests through their scent or chemicals. Growing them near vulnerable plants like tomatoes reduces pest pressure naturally.
Nutrient sharing: Legumes (beans, peas) have a symbiotic relationship with bacteria that fixes nitrogen from the air into the soil. Growing them alongside heavy-feeding plants (like corn or lettuce) means less fertiliser needed.
Physical support and shade: Tall plants (corn, sunflowers) can provide shade for heat-sensitive plants. Sturdy plants can support climbing plants (beans, peas).
Proven companion planting pairs for Australian gardens
Tomato + Basil + Marigold
The classic trio. Basil repels whiteflies and mites. Marigolds deter root nematodes and other pests. Together, they create a pest-resistant tomato patch. This trio works in every Australian climate and is especially valuable in warm zones where pests thrive year-round.
Spacing: 30cm between tomato plants, basil and marigolds in the gaps.
Corn + Beans + Squash (The Three Sisters)
This ancient Indigenous American combination works brilliantly in Australia too. Corn provides a trellis for beans. Beans fix nitrogen, feeding both corn and squash. Squash shades the soil, keeping it cool and moist. One bed of Three Sisters feeds more people with less fertiliser than any single crop.
Spacing: Corn 30cm apart, beans planted when corn is 15cm tall, squash spread between. Works best in temperate and subtropical zones.
Carrot + Onion + Lettuce
Carrots and onions repel each other's major pests (carrot rust fly and onion fly). Lettuce grows low, using space between taller plants. All three mature at different rates, so you harvest continuously without depleting the bed.
Spacing: Rows 20cm apart, thin seedlings for individual space.
Cucumber + Borage + Nasturtium
Borage flowers attract pollinators (crucial for cucumbers) and repel spider mites. Nasturtium is a trap crop — pests prefer it to cucumber, so they leave your fruit alone. Borage and nasturtium are also edible, so you get two crops.
Spacing: Cucumbers on trellis, borage and nasturtium sprawling at the base.
Brassicas (Cabbage, Broccoli, Cauliflower) + Thyme + Chamomile
Thyme and chamomile repel cabbage moths and improve overall plant health. Brassicas are vulnerable to moths (especially in warm climates), and this combination dramatically reduces damage without sprays.
Spacing: Plant thyme and chamomile around brassicas, not directly adjacent.
Peppers + Oregano + Garlic
Garlic is a natural fungicide and pest deterrent. Oregano repels spider mites. Together, they protect peppers (which are susceptible to mites and fungal diseases) in Australian heat. This combination works especially well in subtropical and tropical zones.
Spacing: 40cm between pepper plants, garlic cloves around the perimeter, oregano as a groundcover.
Peas + Radish + Turnip
Peas fix nitrogen, feeding hungry radishes and turnips. Radishes and turnips mature quickly, freeing space for peas to ramble. This trio works great in cool temperate zones and as an autumn/winter crop in warmer areas.
Spacing: Peas on trellis, radishes and turnips between rows.
Strawberries + Borage + Thyme
Borage improves strawberry flavour and repels pests. Thyme deters worms. Both are perennial herbs, so they create a permanent edge around your strawberry bed. Once established, this combination needs minimal intervention.
Spacing: Strawberries in rows, herbs as a border.
Companion planting combinations to avoid
Tomato + Brassicas
Brassicas release compounds that inhibit tomato root development. The combination works, but yields decline. Keep them at least 60cm apart, preferably in different beds.
Fennel + Most vegetables
Fennel releases allelopathic compounds (substances that inhibit other plants' growth). It's best grown alone or with a few tolerant plants like dill. Keep it away from beans, tomatoes, and lettuce.
Dill + Carrots
Dill attracts carrot rust fly, the same pest that targets carrots. Growing them together doubles your pest problem. Choose basil or cilantro instead.
Onions + Beans or Peas
Onions inhibit nitrogen fixation in legumes, so beans and peas produce less. The combination is wasteful. Separate them by at least 60cm.
Quick reference: companion planting pairs at a glance
| Main Plant | Plant With | Why It Works |
|---|---|---|
| Tomato | Basil, marigold, carrot | Repels pests, attracts pollinators |
| Cucumber | Borage, nasturtium, radish | Attracts pollinators, trap crop for pests |
| Lettuce | Carrot, onion, beet, radish | Different root depths, companion herbs |
| Pepper | Garlic, oregano, onion | Natural fungicide and pest control |
| Bean | Corn, squash, carrot, lettuce | Nitrogen fixation feeds other plants |
| Carrot | Onion, lettuce, tomato | Different root depths, pest deterrence |
Tips for successful companion planting
Start small. Test one or two combinations before redesigning your whole garden. Learn what works in your specific microclimate and soil.
Respect spacing requirements. Companion planting doesn't mean crowding. Each plant still needs space to grow. Respect minimum spacing or yields drop.
Rotate your crops. Even with companion planting, rotate beds annually. Don't grow tomatoes + basil in the same spot for five years. Soil pests and diseases build up.
Understand your climate zone. Some companion planting benefits are more pronounced in certain climates. The Three Sisters works better in warm zones. Brassica combinations work better in cool zones. Match combinations to your local conditions — our Australian climate zones guide can help you identify yours.
If you're tracking multiple companion plantings, tools that help you plan garden layouts can be invaluable. Apps designed for your local climate make it even easier to optimize planting combinations for your specific region.
Companion planting isn't complicated, but it does pay attention. Plant thoughtfully, watch how your combinations perform, and refine each year. A well-designed companion planting system grows more food, uses fewer inputs, and actually makes gardening easier. New to gardening? Start with our list of easy plants for Australian beginners.