Basil Companion Plants: What Grows Well With Basil (and What Doesn't)

Basil is one of the most generous companion plants in the garden. Its aromatic volatile compounds — the same oils that make it such a distinctive culinary herb — appear to benefit a range of neighbouring crops by deterring pest insects and masking host-plant scent signals. The tomato-basil pairing is the most famous example, but basil's companion benefits extend further.

Why Basil Makes a Good Companion

Basil continuously releases volatile organic compounds (VOCs) from its leaves — the aromatic chemicals that give it that characteristic scent. These include linalool, eugenol, methyl chavicol, and methyl cinnamate, among others. Commercial insect repellent research has identified many of these compounds as having genuine deterrent effects on specific insects, including aphids, thrips, and whitefly.

In the garden, these compounds diffuse outward from the plant and may disrupt the olfactory host-finding mechanisms of flying pest insects. The radius of effectiveness is relatively short — most of the benefit is concentrated within 60–90 cm of a basil plant. This is why interplanting basil throughout a bed (not just at the edge) is more effective for pest deterrence.

Best Companion Plants For Basil

Tomatoes — The Classic Pairing

The basil-tomato relationship is the most widely practised companion planting tradition globally. Both crops thrive in identical conditions: full sun, warm temperatures (18°C minimum), rich and consistently moist soil, and protection from cold. They can be watered and fertilised on the same schedule with the same inputs.

In terms of pest deterrence, most gardeners growing basil among tomatoes report fewer aphid and whitefly infestations than in tomato beds without basil. The mechanism is believed to be VOC-based disruption of pest host-finding. Whether the effect is prevention or simply reduction, the practical experience is positive enough to make this pairing essentially universal among experienced kitchen gardeners.

Planting guide: One basil plant for every 45–60 cm between tomato plants. Both can be transplanted at the same time after last frost.

Peppers and Aubergines (Eggplants)

Both peppers (Capsicum) and aubergines belong to the Solanaceae family along with tomatoes and share the same warm-season requirements. Basil companions these crops equally well, providing similar pest-deterrent volatile compounds in conditions both plants enjoy. Planting basil among peppers reduces thrip pressure, which is particularly damaging to pepper flowers and fruit set.

Asparagus

Asparagus and basil are reported to repel each other's main pests — basil discourages asparagus beetle while asparagus root exudates deter aphids that attack basil. The relationship works at ground level (asparagus ferns in summer, basil planted between) without significant competition. Asparagus is a perennial that establishes over 2–3 years; basil can be planted between the established ferns each summer as an annual.

Marigolds — Completing the Trio

In a tomato and basil bed, adding French marigolds creates a three-part system: basil for VOC pest deterrence and whitefly disruption, marigolds for nematode protection in the root zone, and the tomatoes benefiting from both. Plant all three together for comprehensive companion coverage.

Root Vegetables (Carrots, Beets, Turnips)

Root vegetables have different pest complexes from basil and do not compete with basil in the root zone (basil roots shallowly while root vegetables extend deeper). Basil's aromatic compounds may deter the flying insects that lay eggs on root vegetable foliage. Interplanting basil between rows of carrots, beets, and turnips adds diversity and potential pest disruption without resource competition.

Plants That Don't Pair Well with Basil

Sage — Traditional Incompatibility

Basil and sage are the most commonly cited incompatible herb pair in companion planting tradition. Some gardeners and older sources claim sage inhibits basil's growth when planted in direct proximity. The evidence is anecdotal rather than experimentally demonstrated, but the claim is consistent enough across gardening literature to warrant keeping a distance of at least 60 cm between the two.

Both plants also have somewhat different water requirements — basil likes consistently moist soil while sage (a Mediterranean herb) prefers drier conditions. This practical incompatibility in mixed containers is real even if the allelopathic claim is uncertain.

Fennel — Keep Isolated

Fennel is allelopathic to almost all other plants, including basil. Its root exudates inhibit germination and growth of neighbouring plants. Keep fennel well away from all other herbs and vegetables — in a container by itself or at the far end of the garden.

Mint — Container Conflict

In open ground, mint and basil can coexist with adequate space. In containers, mint's aggressive spreading root system takes over and outcompetes basil for space, water, and nutrients. Grow mint only in dedicated pots. In the garden, if mint is established nearby, contain it within a buried pot to prevent root spread.

Basil Companion Planting in Containers

Container companion planting with basil is practical and space-efficient:

• Tomato + basil in a large container: Use a container at least 45 cm wide and 40 cm deep. One determinate (bush) tomato variety plus two or three basil plants works well. Both need the same watering frequency and fertiliser schedule.
• Basil + chives: Compatible in a shared pot — similar water requirements and non-competing root zones.
• Basil + parsley: Compatible; both appreciate consistent moisture and regular pinching.
• Basil + oregano: Manageable in adjacent pots, but not ideal in a shared pot — oregano's Mediterranean drought tolerance conflicts with basil's need for consistent moisture.

A Note on Basil and Flavour Claims

The claim that basil improves the flavour of neighbouring tomatoes — a popular piece of gardening folklore — has no rigorous scientific support. Tomato flavour is determined primarily by variety, ripening time (vine-ripened versus picked green), sun exposure during fruit development, and watering regime during fruit fill. Proximity to basil does not measurably change these factors.

This does not make basil less valuable as a companion — the pest-deterrence value is real and practically meaningful. Just don't expect basil proximity to substitute for selecting a flavourful variety and letting tomatoes ripen fully on the vine.