Companion Planting Guide for Australian Vegetable Gardens

Companion planting is the practice of growing certain plants together for mutual benefit. This time-tested technique can increase yields, reduce pest problems, improve pollination, and make more efficient use of garden space. For Australian vegetable gardeners, understanding companion planting transforms a good garden into a great one. This guide covers the essential partnerships and combinations to avoid.

The Science Behind Companion Planting

Companion planting works through several mechanisms. Some plants repel pests with their scent or chemical compounds. Others attract beneficial insects that prey on garden pests. Certain combinations improve soil conditions, while some simply make efficient use of space by combining tall and short plants or fast and slow growers.

Nitrogen fixation is one well-documented benefit. Legumes including beans, peas, and broad beans harbour bacteria in their root nodules that convert atmospheric nitrogen into plant-available forms. Following heavy-feeding crops with legumes replenishes soil nitrogen naturally, reducing the need for added fertilisers.

Pest confusion is another proven mechanism. Monocultures of single crops create easy targets for specific pests. Interplanting with aromatic herbs and flowers disrupts pest navigation and creates habitat for beneficial predators. The resulting diversity mimics natural ecosystems where pest outbreaks are rare.

Tomato Companion Plants

Tomatoes benefit from numerous companion plants. Basil is the classic pairing, with some gardeners claiming it improves tomato flavour while definitely repelling aphids, whiteflies, and mosquitoes. Plant basil between tomato plants or along bed edges for this dual benefit.

Carrots grown near tomatoes help loosen soil with their deep roots, improving drainage for tomato roots. Parsley attracts beneficial hoverflies whose larvae consume aphids. Marigolds planted throughout tomato beds deter nematodes and whiteflies while adding cheerful colour.

Avoid planting tomatoes near brassicas (cabbage, broccoli, cauliflower) as they compete for nutrients. Keep tomatoes away from fennel, which inhibits their growth. Corn should also be separated from tomatoes, as both attract the same earworm pest.

Use our Plant Spacing Calculator to determine how many tomato plants and companions fit in your beds with proper spacing for optimal growth.

Brassica Family Companions

Cabbages, broccoli, cauliflower, kale, and Brussels sprouts face significant pest pressure from cabbage moths and aphids. Strategic companion planting helps protect these valuable crops without chemical intervention.

Aromatic herbs excel as brassica companions. Rosemary, sage, thyme, and mint confuse cabbage moths seeking host plants. Nasturtiums planted nearby act as trap crops, attracting aphids away from brassicas. Dill and fennel attract beneficial wasps that parasitise caterpillars.

Onions and garlic planted among brassicas deter a range of pests with their strong scent. Celery is another good companion, with its strong smell masking brassica plants from pests. Beetroot grows well alongside brassicas without competition.

Keep brassicas away from strawberries and tomatoes, which compete for nutrients. Avoid planting near grapes, which are stunted by brassica root secretions. Do not follow brassicas with brassicas in rotation, as this encourages pest and disease buildup.

Cucurbits and Their Partners

Cucumbers, zucchini, pumpkins, and melons belong to the cucurbit family. These plants benefit from companions that attract pollinators and deter pests while not competing for the significant space cucurbits require.

The Three Sisters planting combines corn, beans, and squash in a traditional polyculture. Corn provides structure for beans to climb, beans fix nitrogen benefiting all three plants, and squash vines shade soil to suppress weeds and retain moisture. This sustainable system has been used for thousands of years.

Radishes planted among cucurbits repel cucumber beetles with their pungent roots. Marigolds deter squash bugs and attract pollinators needed for fruit set. Sunflowers attract bees while providing vertical interest in the garden.

Avoid planting potatoes near cucurbits, as both are susceptible to blight that spreads between them. Strong herbs like sage may inhibit cucurbit growth and should be planted separately.

Allium Family Benefits

Onions, garlic, leeks, shallots, and chives offer powerful pest-deterrent properties. Their strong sulphur compounds repel a wide range of insect pests, making them valuable companions throughout the vegetable garden.

Plant garlic near roses to deter aphids, or alongside carrots to mask their scent from carrot flies. Onions grown between lettuce and other leafy greens protect against aphids while making efficient use of space. Chives edging garden beds create an aromatic barrier against many pests.

Keep alliums away from beans and peas, as allium root secretions inhibit legume growth. Asparagus also grows poorly near onion family members. These combinations should be separated by at least a metre or grown in different beds entirely.

Creating a Companion Planting Layout

Planning a companion planting layout requires considering plant heights, spreads, and growing seasons alongside compatibility. Tall plants should be positioned to avoid shading sun-loving neighbours. Fast-maturing crops can occupy space while slow growers establish.

Design beds with a mix of plant families rather than monocultures. This diversity creates natural pest resistance and efficient nutrient cycling. Include flowers and herbs throughout vegetable beds rather than segregating them in separate areas.

Record your observations of what works in your specific garden. Companion planting principles provide guidelines, but local conditions, specific varieties, and microclimate all influence outcomes. Over time, you will develop knowledge of which combinations perform best in your garden.

Companion planting transforms vegetable gardening from a battle against pests into a harmonious system where plants support each other. By understanding beneficial relationships and avoiding harmful combinations, you create a more productive, resilient, and enjoyable garden. Plan your companion planting layout using our Plant Spacing Calculator to determine how many of each vegetable will fit your beds.