Companion planting is the practice of growing certain plants together for mutual benefit. In the confined space of a raised garden bed, choosing complementary plant combinations becomes even more important. The right companions can improve growth, deter pests, attract pollinators, and maximise your harvest from limited space. This guide explores proven companion planting strategies specifically suited to raised bed vegetable gardens.
The Science Behind Companion Planting
Companion planting encompasses several distinct mechanisms, each offering different benefits to your garden ecosystem.
Nutrient Sharing and Fixation
Legumes (beans, peas, and their relatives) host nitrogen-fixing bacteria in their root nodules, converting atmospheric nitrogen into plant-available forms. Growing nitrogen-hungry vegetables like corn or brassicas near legumes takes advantage of this natural fertiliser production. The famous "Three Sisters" planting of corn, beans, and squash practiced by Indigenous Americans demonstrates this principle beautifully.
Pest Deterrence
Many herbs and flowers produce aromatic compounds that confuse or repel pest insects. Basil near tomatoes masks the tomato scent that attracts certain pests; marigolds release chemicals that deter nematodes and whiteflies. Some companion plants serve as "trap crops," attracting pests away from your main vegetables—nasturtiums famously lure aphids, protecting nearby plants.
Interplant aromatic herbs throughout your raised bed rather than grouping them in one area. Distributed plantings maximise the pest-confusing effect of their scents.
Beneficial Insect Attraction
Flowering companions attract pollinators and predatory insects that control pests naturally. Allowing some herbs to flower provides nectar and pollen for hoverflies, parasitic wasps, and other beneficial insects. A diverse planting supports a diverse insect community, creating natural balance.
Physical Support and Protection
Tall plants can provide shade for heat-sensitive crops during summer or support for climbing vegetables. Corn stalks support climbing beans; leafy greens thrive in the dappled shade of taller tomato plants during hot weather. Strategic placement creates beneficial microclimates within your raised bed.
Classic Companion Plant Combinations
These time-tested combinations work reliably in Australian raised beds.
Tomatoes and Basil
Perhaps the most famous companion pairing, tomatoes and basil benefit each other in the garden as much as on the plate. Basil's strong fragrance is believed to repel tomato hornworms and aphids, while some gardeners report improved tomato flavour when grown with basil. Plant basil between tomato plants or around the bed perimeter.
Carrots and Onions
The strong scent of onions masks the carrot smell that attracts carrot fly, while carrots are said to repel onion fly. Alternate rows of carrots and onions, or interplant spring onions throughout carrot plantings. Both crops occupy similar growing conditions and mature at complementary times.
Many companion combinations work through scent masking—interplanting aromatic crops disrupts pests' ability to locate their target vegetables by smell.
Brassicas and Dill
Dill attracts beneficial wasps that parasitise cabbage caterpillars, providing natural pest control for broccoli, cauliflower, cabbage, and other brassicas. Allow dill to flower rather than harvesting all of it. The tiny flowers are highly attractive to beneficial insects. Plant dill near but not directly under brassicas to avoid competition.
Corn, Beans, and Squash
The traditional Three Sisters combination remains effective today. Corn provides climbing support for beans, beans fix nitrogen that feeds the heavy-feeding corn, and squash spreads across the ground to shade soil and reduce moisture loss. In raised beds, use compact squash varieties or train vines to cascade over bed edges.
Lettuce and Tall Vegetables
Lettuce bolts (goes to seed) quickly in hot weather. Planting lettuce in the shade of taller crops like tomatoes, corn, or trellised beans extends the harvest season by providing cool microclimate conditions. As summer progresses, the increasing shade from growing tall crops keeps lettuce productive longer.
Plants to Keep Separate
While many plants grow well together, some combinations should be avoided.
Allelopathic Effects
Some plants release chemicals that inhibit the growth of neighbours. Fennel is notoriously antisocial, suppressing growth of most vegetables—grow it separately from your main raised bed. Sunflowers also produce growth-inhibiting compounds, though their benefits for pollinators may outweigh this drawback when placed at bed edges.
Resource Competition
Plants with similar needs may compete rather than complement each other. Avoid planting multiple heavy feeders together without adequate fertilisation—tomatoes next to corn next to brassicas creates intense competition for nutrients. Space heavy feeders apart and interplant with lighter feeders or nitrogen-fixing legumes.
Keep potatoes away from tomatoes and other nightshades. These relatives share diseases including devastating late blight, and proximity increases infection risk for all plants.
Problematic Pairings
Certain specific combinations cause problems:
- Beans and alliums: Onions and garlic inhibit bean growth
- Brassicas and strawberries: Both suffer from increased pest problems
- Carrots and dill: Despite dill benefiting brassicas, it can cross-pollinate with carrots and attracts pests that affect both
- Cucumber and aromatic herbs: Strong herbs can affect cucumber flavour
Planning a Companion-Planted Raised Bed
Designing an effective companion planting scheme requires considering plant heights, spread, timing, and beneficial relationships.
Vertical Layering
Think in three dimensions when planning your bed. Tall plants (corn, staked tomatoes, trellised beans) form the upper layer, medium plants (capsicums, bush beans, broccoli) occupy the middle, and ground-hugging plants (lettuce, strawberries, spreading herbs) fill the lower layer. This maximises light capture and space utilisation.
Edge Plantings
Use bed edges strategically. Cascading plants like nasturtiums and strawberries soften hard edges while producing food. Aromatic herbs planted around the perimeter create a fragrant barrier that may deter approaching pests. Compact flowers like alyssum and marigolds attract beneficial insects without competing with vegetables for space.
Succession and Timing
Consider plant lifecycles when planning companions. Fast-maturing crops like radishes and lettuce can be interplanted with slow-growing vegetables like tomatoes and peppers. By the time the tomatoes need space, the quick crops have already been harvested. This "relay planting" approach maximises harvest from limited space.
Flowers in the Vegetable Garden
Including flowers in your raised bed isn't just aesthetically pleasing—it's functionally important for a healthy garden ecosystem.
Marigolds
French marigolds release compounds that suppress nematodes in soil and repel whiteflies above ground. Their bright flowers attract pollinators and predatory insects. Plant marigolds throughout the bed, especially near tomatoes, capsicums, and beans. Choose compact varieties for raised beds.
Calendula
Calendula (pot marigold) attracts hoverflies whose larvae devour aphids. The flowers are also edible, adding colour to salads. Calendula self-seeds readily, so you'll have volunteers in subsequent seasons once established.
Alyssum
Sweet alyssum produces abundant tiny flowers that attract beneficial insects, particularly parasitic wasps that control caterpillars. Its low-growing habit makes it ideal as a living mulch beneath taller vegetables. Plant alyssum around bed edges and let it spread.
Borage
Borage is a bee magnet with edible flowers and leaves. It's claimed to improve tomato growth and flavour when planted nearby. One borage plant provides substantial insect habitat—it's vigorous, so one per bed is usually sufficient.
Practical Implementation
Start companion planting gradually rather than attempting complex schemes immediately. Begin with a few proven combinations and observe results in your specific conditions. What works in one garden may differ slightly in another due to local pest populations, climate variations, and soil conditions.
Keep records of your plantings and note which combinations seem most effective. Over time, you'll develop customised companion planting knowledge for your particular raised bed garden. The goal isn't rigid adherence to rules but creating a diverse, balanced ecosystem where plants support each other's growth and health.
Remember that companion planting supplements but doesn't replace good gardening practices. Healthy soil, adequate water, and appropriate plant spacing remain essential foundations. With companions adding an extra layer of natural pest control and productivity, your raised bed becomes a thriving community rather than just a collection of individual plants.