Basil Companion Plants
Basil grows best alongside companions that pull their weight. Reliable partners include Tomato, Pepper, Eggplant, and Lettuce. Just as important is what to keep apart — avoid planting basil near Fennel, Sage, rosemary, thyme, oregano and lavender, and Rue. Every pairing below comes with the specific reason behind it and how to stack them by layer and season.
Grow Basil with: Tomato, Pepper, Eggplant, Lettuce, and more below.
Keep it away from: Fennel, Sage, rosemary, thyme, oregano and lavender, Rue.
Best companions for Basil
Each pairing below earns its place — the reason, when to plant it, and where it sits in the bed.
Basil VOCs (linalool, chavicol) prime tomato JA/MAPK/ROS wound defenses, roughly halving armyworm larval growth; field/greenhouse work also shows reduced thrips damage and fewer hornworm/armyworm moth eggs on basil-protected tomatoes.
Layout: Transplant both after last frost; keep basil within ~1 m (3 ft) of tomatoes, since the protective volatile effect drops off sharply beyond that distance.
Both are warm-season, moisture- and fertility-loving crops long interplanted in the same bed; if basil is allowed to flower, its nectar and pollen can support lacewings and hoverflies that prey on aphids and thrips near the peppers.
Layout: Set both out after the soil warms; interplant basil between pepper plants at ~12-18 in spacing.
In replicated trials, basil intercropped with eggplant raised green lacewing (Chrysopa pallens) colonization 72-92% and made green peach aphid numbers crash faster; the highest-density basil arrangement worked best.
Layout: Interplant basil densely among eggplants at transplant; tighter basil spacing gives stronger lacewing recruitment.
Traditionally interplanted: fast lettuce fills the ground layer as living mulch under young basil, using space efficiently, and basil's later canopy casts light afternoon shade that can delay heat-triggered bolting; harvest lettuce as basil bushes out.
Layout: Interplant quick lettuce around basil transplants in spring; harvest the lettuce as basil bushes out and begins to shade it.
French-marigold roots exude alpha-terthienyl, a thiophene toxic to root-knot nematodes (Meloidogyne); a dense pre-crop stand can suppress populations up to ~99%, protecting nematode-susceptible basil grown afterward.
Layout: Strongest as a dense pre-crop cover for ~2 months the prior season; scattered interplants give only modest nematode benefit but still add pollinator flowers.
Borage's blue flowers are a heavy nectar/pollen source for bees and host green lacewings and braconid wasps; gardeners credit it with fewer tomato hornworms via wasp parasitism, but that pest effect is anecdotal, not trial-proven.
Layout: Sow borage at the bed edge in spring; it self-sows and blooms right through basil's season.
Their tiny umbel flowers offer accessible nectar/pollen that fuel parasitic wasps and syrphid (hover) flies whose larvae devour aphids, thrips, and caterpillar eggs; extension insectary lists rank them top predator-attractors.
Layout: Let cool-season cilantro/dill bolt into flower as basil establishes in early summer; the flowering (not leafy) stage is what feeds the beneficials.
Nasturtium foliage is strongly preferred by aphids (and cabbage whites, cucumber beetles), pulling them off nearby crops onto a sacrificial trap; its flowers also draw aphid-eating hoverflies. Needs active removal of infested foliage.
Layout: Interplant at the bed margin; scout weekly and cut out aphid-loaded stems before colonies spill back onto crops - trap cropping is active, not passive.
How to lay it out
Stack companions by layer so they share light, root space, and time instead of competing — the permaculture way to pack more into one bed.
Layers for a Basil guild. Tags mark companions planted on a delay so they fill in as the bed matures.
Plants to avoid near Basil
Fennel roots and residues release allelochemicals (anethole and related compounds) that inhibit germination and seedling growth of most garden plants, basil included; it is antagonistic to nearly everything and is best isolated in its own bed or container.
Not chemical antagonism but a cultural mismatch: these herbs want lean, dry, sharply drained soil and infrequent water, while basil needs steady moisture and fertility, so co-planting forces a watering/feeding compromise that stresses one side.
Rue is the classic 'keep away from basil' plant - it is allelopathic (alkaloids and coumarins can stunt neighbors), but the specific basil antagonism is long-standing garden lore rather than trial-documented.