Companion Planting Guide UK: Natural Pest Control & Better Harvests

Last Updated: December 2025

Companion planting harnesses the relationships between different plants to create healthier, more productive gardens. Rather than relying on chemical inputs, companion planting uses biodiversity to deter pests, attract beneficial insects, improve soil, and increase yields naturally.

This traditional practice, refined over centuries, offers modern gardeners an ecological approach to pest management whilst creating beautiful, abundant gardens. For UK growers, companion planting works with our climate and seasons to build resilient growing spaces.

Understanding Companion Planting

How Companion Planting Works

Plants influence their neighbours in multiple ways:

Chemical Interactions: Some plants release compounds through their roots that either help or hinder neighbouring plants. Allelopathy is the scientific term for this chemical signalling.

Pest Confusion: Aromatic plants release strong scents that mask the smell of plants pests seek. Mixed planting makes it harder for pests to locate their targets.

Trap Cropping: Some plants attract pests away from more valuable crops. Nasturtiums, for example, draw aphids whilst leaving nearby vegetables unaffected.

Beneficial Attraction: Flowers planted alongside vegetables attract pollinators and predatory insects that control pest populations naturally.

Structural Support: Some plants provide physical support for others. The “Three Sisters” (corn, beans, squash) exemplifies this: corn supports climbing beans whilst squash shades soil.

Soil Improvement: Legumes fix nitrogen from the air, making it available to neighbouring plants. Deep-rooted plants bring up nutrients from subsoil.

What Companion Planting Isn’t

Companion planting works through subtle influence, not magic. It:

• Doesn’t eliminate pests completely (that would remove food for beneficial predators)
• Works best as part of broader ecological gardening practices
• Requires some experimentation to find what works in your specific conditions
• Isn’t a replacement for healthy soil and proper plant care

The Science Behind Companion Planting

Evidence-Based Combinations

Whilst traditional wisdom informs companion planting, scientific research increasingly validates specific combinations:

Tomatoes and Basil: Studies show basil planted near tomatoes may reduce whitefly populations and potentially improve tomato flavour (though flavour improvement remains debated).

Brassicas and Alliums: Research confirms alliums (onions, garlic) planted near brassicas (cabbage family) reduce aphid and cabbage white butterfly populations.

French Marigolds and Various Crops: Marigold roots release compounds that suppress nematode populations in soil whilst flowers attract hoverflies (aphid predators).

Carrots and Onions: Classic combination: onion smell masks carrots from carrot fly; carrot foliage confuses onion fly.

Garden Folklore vs. Facts

Some companion planting claims lack scientific support:

Myth: Planting basil with tomatoes significantly increases yield Reality: No consistent evidence; any increase likely due to improved pollinator presence

Myth: Companion planting eliminates need for any pest control Reality: Companion planting reduces but doesn’t eliminate problems

Myth: All plant combinations either help or harm each other Reality: Most plants are neutral toward most others

Approach companion planting as one tool among many rather than a complete solution.

Companion Planting for Common UK Vegetables

Tomatoes

Good Companions:

• Basil: Potentially deters whitefly; attracts pollinators
• Marigolds: Deters whitefly and attracts beneficial insects
• Carrots: Don’t compete for nutrients; complementary root depths
• Parsley: Attracts hoverflies
• Asparagus: Tomatoes may deter asparagus beetle

Bad Companions:

• Brassicas: Compete for nutrients; incompatible growth requirements
• Potatoes: Both susceptible to blight; planting together increases risk
• Fennel: Inhibits tomato growth

Brassicas (Cabbage, Kale, Broccoli, Cauliflower)

Good Companions:

• Onions and Garlic: Deter aphids and cabbage white butterflies
• Nasturtiums: Act as trap crop for aphids
• Dill and Chamomile: Attract beneficial wasps that parasitise caterpillars
• Celery: May deter cabbage white butterfly
• Mint: Strong scent confuses pests (plant in pots; highly invasive)
• Rosemary and Sage: Aromatic herbs that deter cabbage moths

Bad Companions:

• Strawberries: Compete for nutrients
• Tomatoes: Incompatible feeding requirements
• Pole beans: Shade brassicas, which need full sun

Carrots

Good Companions:

• Onions and Leeks: Classic combination; onion scent masks carrots from carrot fly
• Rosemary and Sage: Strong scents deter carrot fly
• Tomatoes: Complementary root systems; don’t compete
• Lettuce: Fast-growing; harvested before carrots need space
• Chives: Deter aphids

Bad Companions:

• Dill: May reduce carrot yield
• Parsnips: Both attract carrot fly; planting together concentrates problems

Beans and Peas

Good Companions:

• Corn: Provides support for climbing beans
• Squash: Completes “Three Sisters” combination; shades soil
• Carrots: Beans fix nitrogen; carrots don’t compete
• Cucumber: Similar water needs
• Potatoes: Beans fix nitrogen that potatoes use
• Radishes: Quick crop harvested before beans need space

Bad Companions:

• Onions and Garlic: May inhibit bean growth
• Fennel: Inhibits most plants, including beans
• Sunflowers: Allelopathic effects may reduce bean germination

Potatoes

Good Companions:

• Beans: Fix nitrogen that potatoes utilise
• Horseradish: May deter potato beetle (though not common pest in UK)
• Nasturtiums: Attract aphids away from potatoes
• Marigolds: Deter various pests and beneficial for soil

Bad Companions:

• Tomatoes: Both susceptible to blight
• Sunflowers: May inhibit potato growth
• Squash and Cucumber: Compete for space and nutrients

Lettuce and Salads

Good Companions:

• Carrots: Lettuce harvested before carrots need space
• Radishes: Quick harvest doesn’t interfere
• Onions: Help deter aphids
• Chives: Deter aphids
• Nasturtiums: Attract aphids away from lettuce

Bad Companions:

• Parsley: May inhibit lettuce growth
• None significant; lettuce is generally compatible

Onions, Garlic, and Leeks

Good Companions:

• Carrots: Onion scent deters carrot fly
• Brassicas: Deter cabbage pests
• Tomatoes: May reduce fungal diseases
• Lettuce: Compatible space requirements
• Chamomile: Improves onion flavour (traditional belief; limited evidence)

Bad Companions:

• Beans and Peas: May inhibit legume growth
• Sage: May inhibit allium growth

Squash, Courgettes, Pumpkins

Good Companions:

• Corn: Provides support; squash shades weeds
• Beans: Fix nitrogen; corn provides structure
• Nasturtiums: Deter squash bugs
• Radishes: Deter squash vine borers
• Marigolds: General pest deterrent

Bad Companions:

• Potatoes: Compete for space and nutrients

Companion Planting for UK Herb Gardens

Herb Companions for Pest Control

Rosemary:

• Deters carrot fly, bean beetles, cabbage moths
• Plant near brassicas, carrots, beans
• Attracts bees and beneficial insects
• Perennial; leave in place year-round

Sage:

• Repels cabbage moths and carrot flies
• Good near brassicas and carrots
• Attracts beneficial insects
• Avoid planting near cucumbers

Lavender:

• Attracts pollinators
• General pest deterrent due to strong scent
• Excellent near most vegetables and fruits
• Deters moths and fleas

Thyme:

• Attracts beneficial insects
• Deters cabbage worms
• Ground cover that suppresses weeds
• Good near most vegetables

Mint:

• Very strong scent deters many pests
• Plant in containers (highly invasive)
• Good near brassicas and tomatoes
• Deters ants and aphids

Dill:

• Attracts beneficial wasps and hoverflies
• Good near brassicas (until it gets large)
• Host plant for swallowtail butterflies
• Keep away from carrots

Chamomile:

• Attracts beneficial insects
• Traditional “physician plant” believed to improve nearby plant health
• Good near onions and brassicas

Basil:

• Plant near tomatoes and asparagus
• Attracts pollinators
• May deter aphids, asparagus beetles, and tomato hornworm (not UK pest)

Herbs as Trap Crops

Nasturtiums: Highly attractive to aphids, blackfly, and cabbage white butterflies. Plant near:

• Brassicas
• Tomatoes
• Beans
• Squash

Check nasturtiums regularly and remove heavily infested leaves.

Creating a Companion Planting Design

Planning Your Layout

Polyculture Beds: Rather than planting vegetables in rows of a single crop, mix compatible plants:

• Tomatoes surrounded by basil and marigolds
• Carrots intercropped with onions
• Brassicas edged with aromatic herbs

Pest Confusion Principle: Mixed plantings make it harder for pests to locate target plants. Large blocks of single crops create pest magnets.

Successional Planting: Use fast-growing companions (lettuce, radishes) between slow-growing main crops. Harvest quick crops before larger plants need space.

Sample UK Companion Planting Schemes

Scheme 1: Traditional Cottage Garden Bed

• Centre: Tomatoes with basil and French marigolds
• Edges: Carrots intercropped with spring onions
• Corners: Nasturtiums as trap crops
• Between plants: Lettuce as quick harvest

Scheme 2: Brassica Protection Bed

• Centre: Kale and cabbage
• Between brassicas: Onions and garlic
• Edges: Rosemary, thyme, and sage
• Nasturtiums at corners

Scheme 3: Productive Small Space

• Climbing beans on support
• Lettuce and radishes at base (harvested early)
• Marigolds throughout
• Chives at edges

Scheme 4: Three Sisters (UK Adaptation)

• Sweetcorn planted in blocks (not UK’s best crop but possible)
• Climbing beans once corn is 15cm tall
• Squash or courgettes between corn plants
• Nasturtiums at edges

Flowers as Companion Plants

Attracting Pollinators

Vegetables need pollination (especially squash, tomatoes, beans, peas). Flowers ensure abundant pollinator presence:

Throughout Season:

• Calendula (pot marigold): Attracts hoverflies and bees; edible
• Borage: Beloved by bees; self-seeds readily
• Phacelia: Attracts huge numbers of beneficial insects
• Cornflowers: Support many beneficial insects

Spring:

• Forget-me-nots
• Wallflowers
• Honesty

Summer:

• Lavender
• Cosmos
• Sunflowers (plant away from beans and potatoes)

Autumn:

• Asters
• Sedum (particularly ‘Autumn Joy’)

Flowers That Deter Pests

French Marigolds (Tagetes patula):

• Suppress soil nematodes
• Deter whitefly
• Attract hoverflies (aphid predators)
• Plant throughout vegetable garden

Nasturtiums:

• Trap crop for aphids and caterpillars
• Attract pollinators
• Edible flowers and leaves
• Self-seed readily

Calendula (Pot Marigold):

• Attracts hoverflies and lacewings
• Deters aphids
• Edible petals
• Self-seeds

Month-by-Month Companion Planting for UK Gardens

March-April

Plant:

• Early lettuce with radishes
• Onion sets with carrots
• Broad beans with savory

Direct Sow:

• Carrots with spring onions
• Peas with radishes
• Early brassicas

May

Plant Out:

• Tomatoes with basil
• Courgettes with nasturtiums
• Squash in Three Sisters formation

Sow:

• Beans with carrots
• More salads with radishes

June-July

Plant:

• Late brassicas with herbs
• Succession salads
• French marigolds throughout beds

Maintain:

• Remove diseased foliage
• Monitor trap crops
• Thin companion plants if overcrowded

August-September

Plant:

• Autumn salads with Japanese onions
• Garlic (October) with strawberries

Clear:

• Spent plants
• Allow beneficial insects time to move before complete clearance

Troubleshooting Companion Planting

“My companions aren’t stopping all pests”

Remember: Companion planting reduces pest pressure but doesn’t eliminate it. Expect some pest damage. Success means manageable levels, not zero pests.

“Plants are overcrowded”

Solution: Thin companions as needed. Better spacing with fewer plants beats overcrowding. Some companions (like lettuce) are intended as quick crops harvested before main crops expand.

“Nothing seems to be working”

Check:

• Soil health (healthy soil grows healthy plants)
• Watering (stressed plants more susceptible to pests)
• Timing (ensure you planted at appropriate season)
• Expectations (companion planting helps but isn’t magic)

Companion Planting and Biodiversity

Beyond Pest Control

Companion planting creates biodiverse gardens that support entire ecosystems:

• Mixed planting provides varied habitat
• Continuous flowering feeds pollinators
• Structural diversity shelters beneficial insects
• Year-round interest supports wildlife through seasons

Creating Layers

Ground Layer: Low-growing herbs (thyme), salads, strawberries Mid Layer: Vegetables, annual herbs, flowers Tall Layer: Beans on supports, tomatoes, tall flowers

Layered planting maximises space whilst creating microhabitats.

Related Resources

For more on natural gardening:

• Best Beginner Houseplants UK
• How to Propagate Houseplants

Final Thoughts

Companion planting transforms gardens from monocultures into diverse ecosystems. Rather than fighting nature with chemicals, you’re working with natural relationships to create balanced, productive spaces.

Start simple. Try one or two proven combinations this season. Observe what works in your specific conditions. Gradually build complexity as you learn what thrives in your garden’s unique microclimate.

The garden you create—buzzing with pollinators, supporting beneficial predators, producing abundant harvests—becomes more than a food source. It becomes a small refuge for biodiversity, a teacher of ecological principles, and a daily reminder that the most sustainable solutions often come from observing and cooperating with nature.