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Tomatoes, basil, onions, marigolds and herbs sharing a drip-irrigated vegetable bed
Reviewed August 2026
Gardening in Spain

Companion planting without the garden myths

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Companion planting is most useful when it describes observable design choices: mixing crops, keeping flowers near vegetables, using space at different heights and avoiding a large block of one host plant. It becomes less reliable when every pairing is presented as a proven repellent or growth tonic.

Benefits you can plan for

Flowers with accessible pollen and nectar can support hoverflies, bees and other insects. Herbs or onions around a taller crop can cover otherwise bare ground. A mixed bed may also make it harder for a pest to move directly from one identical plant to the next. None of these effects makes inspection unnecessary.

In a dry Spanish garden, water is the limiting resource. Plants sharing a bed must still have compatible irrigation needs and enough air around their leaves. Crowding basil, marigolds and tomatoes into a colourful tangle can increase humidity and disease while roots compete for a narrow wet strip.

Build a testable bed

  1. Place tomatoes or other tall crops where they will not shade the whole bed.
  2. Run drip irrigation to each root zone and check delivery rather than watering by appearance.
  3. Add compact flowers in repeated groups, leaving access for harvest and pruning.
  4. Use culinary herbs where their sun, soil and water needs fit.
  5. Record pest levels and yield, then change one part of the design next season.

French marigolds have evidence for suppressing some soil nematodes when used in particular rotations, but that is not the same as a universal protective border. Aromatic plants may confuse or deter some insects in a study setting, yet garden results depend on density, timing and species. Treat confident lists of "good" and "bad" neighbours as hypotheses, not rules.

Diversity beyond flowers

Healthy soil, mulch, crop rotation and non-crop shelter all contribute to a resilient plot. Let some herbs flower, provide a shallow water source which cannot trap insects and tolerate minor cosmetic feeding. Avoid spraying open flowers. A bed designed to attract beneficial insects cannot work if those insects are removed with the pests.

Sources and review

This guide was reviewed in August 2026 using the Royal Horticultural Society companion-planting review and its guidance on gardening for wildlife.