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Companion Planting Seed Guide (UK)

Companion planting is the age-old practice of growing certain plants together to benefit one another—whether it's by deterring pests, improving growth, or enhancing flavour. For UK growers, especially those working with small plots, allotments, or raised beds, companion planting offers a low-cost, organic method to boost success in the veg patch without relying on chemicals.

What Is Companion Planting?

Companion planting is about pairing plants that either help each other grow or protect one another. Some companions deter pests, attract pollinators, or improve soil conditions. Others simply get along because they don’t compete for nutrients or space.

  • Pest deterrents (e.g., onions repelling carrot fly)
  • Pollinator attractors (e.g., borage attracting bees)
  • Soil enhancers (e.g., legumes fixing nitrogen)
  • Growth supporters (e.g., tall plants giving shade or support)

Full Companion Planting Chart for Common UK Veg

Main Crop Good Companions Notes
Beans (all types) Sweetcorn, Radish, Cucumber, Marigold Fix nitrogen; benefit from pollinator flowers
Beetroot Onions, Lettuce, Kohl Rabi Similar soil needs; shallow roots complement deep ones
Brassicas Dill, Mint (in pots), Chamomile, Onion Repel cabbage moth/whitefly; herbs increase vigour
Carrots Onions, Leeks, Rosemary, Chives Onions mask scent; herbs confuse carrot root fly
Courgettes Borage, Nasturtium, Marigold Pollinator attractors; nasturtiums distract aphids
Cucumbers Beans, Dill, Sunflowers, Nasturtium Beans enrich soil; sunflowers offer shade
Leeks Carrots, Celery, Onion, Chard Repel each other's key pests
Lettuce Chives, Carrots, Beetroot, Radish, Dill Good mix of root depths; chives deter aphids
Onions Carrots, Beets, Lettuce, Chamomile, Parsley Carrot fly deterrent; some herbs improve growth
Parsnips Onions, Peas, Garlic, Lettuce Avoid planting with carrots to reduce pest load
Peas Radish, Carrots, Turnips, Cucumbers Fix nitrogen; improve soil for neighbours
Potatoes Horseradish, Beans, Cabbage, Marigold Horseradish deters beetle; marigolds reduce nematodes
Sweetcorn Beans, Courgette, Pumpkin, Peas Classic three sisters combo (UK-suited varieties)
Tomatoes Basil, Marigolds, Onion, Garlic, Nasturtiums Basil boosts flavour; marigolds deter whitefly
Turnips Peas, Chives, Cabbage Cool-loving; benefit from legume nitrogen

Companion Herbs in the UK Veg Garden

Herb Benefits & Pest Control Best Paired With
Basil Repels aphids, improves growth/flavour Tomatoes, Peppers
Borage Attracts bees; deters hornworms Strawberries, Courgettes, Tomatoes
Chamomile Strengthens neighbouring plants Brassicas, Onions, Leeks
Chives Deters aphids, slugs Carrots, Lettuce, Roses
Coriander Repels aphids, spider mites Spinach, Carrots
Dill Attracts hoverflies, ladybirds Brassicas, Courgettes, Lettuce
Mint Deters flea beetles, ants, aphids Brassicas (keep in pot)
Parsley Attracts hoverflies, enhances health Tomatoes, Asparagus
Rosemary Repels carrot fly, cabbage moth Carrots, Cabbage
Sage Deters cabbage white butterfly Brassicas
Thyme Deters whitefly Brassicas, Aubergine

Common Trap Crops Used in UK Growing

Trap Crop Attracts Pests Protects Main Crop
Nasturtium Aphids, cabbage white butterfly Brassicas, Beans, Squash
Radish Flea beetles Lettuce, Spinach, Rocket
Marigolds Whitefly, aphids Tomatoes, Peppers, Courgettes
Mustard Cabbage root fly Brassicas (use as sacrificial crop)
Turnip Greens Slugs Lettuce, Young brassica seedlings
Collards Caterpillars Kale, Broccoli, Cabbage

Tip: Sacrificial trap crops should be planted a few weeks earlier than your main crop, then monitored and removed if overrun.

Incompatible Plantings (What Not to Grow Together)

Plant 1 Avoid Planting With Reason
Beans Onions, Garlic Alliums may inhibit nitrogen-fixing bacteria
Potatoes Tomatoes, Aubergines All susceptible to blight and similar pests
Carrots Parsnips Compete for root space and nutrients; attract similar pests
Fennel Almost everything Strong allelopathic compounds suppress neighbours
Cabbage Strawberries Share pests and reduce brassica growth
Tomatoes Sweetcorn Both vulnerable to corn earworm (rare in UK)

Companion Layout Ideas for Small UK Spaces

Carrot + Onion Row Spacing

Alternate rows of carrots and onions or leeks to confuse each other's pests.

Tomato + Basil + Marigold Triangle

A sunny patio combo: tomatoes in large pots, surrounded by marigolds and basil.

Courgette + Nasturtium Border

Edge courgette beds with nasturtiums to trap aphids and boost bee visits.

Lettuce Under Sweetcorn or Beans

Intercrop quick-growing lettuce below taller shade-giving plants in summer.

Brassica Bed with Herb Borders

Line a cabbage or kale bed with sage, thyme, or dill to naturally deter pests.

UK Timing Tips for Companion Planting

  • Early Spring: Sow trap crops (e.g. radish, mustard) 2–3 weeks before main crops.
  • Mid Spring: Start companions like basil and marigold indoors or under cover.
  • Late Spring to Summer: Direct sow dill, coriander, and fast-growing companions.
  • Succession Sow: Use lettuce and radish around slower crops like tomatoes for space efficiency.