How to Grow Tomato

Basil emits linalool, eugenol, and other volatile terpenes that repel thrips and whiteflies from nearby tomatoes through direct olfactory deterrence, while some studies suggest root exudate interactions may subtly enhance tomato fruit flavour. Plant basil 30 cm from tomato stems so neither plant shades the other's lower leaves.

Tomato foliage releases alkaloid-rich volatile compounds that mask the scent signals carrot fly (Psila rosae) uses to locate its host, reducing egg-laying near carrot roots. Interplant tomatoes and carrots in alternating rows, keeping tomatoes upwind so their scent drifts over the carrot foliage.

Onions release diallyl disulphide and allicin volatiles that interfere with the host-location behaviour of aphids and spider mites — both significant tomato pests. Plant onions in a dense border or every other plant along tomato rows; their shallow roots don't compete with the deeper tomato root system.

Parsley's umbel flowers recruit parasitic wasps and hoverflies whose larvae hunt tomato hornworm eggs and aphid colonies on nearby plants. Allow parsley to bolt and flower rather than harvesting it all — the flat blooms are particularly attractive to Trichogramma wasps that parasitise hornworm eggs before they hatch.

French marigolds (Tagetes patula) secrete alpha-terthienyl from their roots — a thiophene compound toxic to root-knot nematodes — while their above-ground scent confuses and repels whiteflies through terpene interference. Plant them as a dense perimeter around tomato beds and allow some to dry and reseed for continuous nematode suppression year after year.

Nasturtiums act as a sacrificial trap crop for aphids, particularly black bean aphid and peach-potato aphid, whose colonies preferentially colonise nasturtium's glucosinolate-rich leaves over tomato foliage. Position nasturtiums at the bed edges and check them weekly — remove stems with dense colonies before winged aphids disperse back to the tomatoes.

Peppers and tomatoes share near-identical growing requirements — warm soil, full sun, consistent moisture, and moderate nitrogen — making them efficient companions that can share the same irrigation and feeding schedule. Their similar height also means neither shades the other when planted at standard 45–60 cm spacing.

Chillies and tomatoes have virtually the same cultural requirements and are susceptible to overlapping but not identical pest sets, so they benefit from shared growing conditions without amplifying each other's disease risks. Grouping them together also simplifies greenhouse or polytunnel management where warm, humid conditions suit both.

Garlic's allicin and diallyl disulphide root exudates diffuse through the soil and repel red spider mites, which congregate on the undersides of tomato leaves during hot, dry spells. Plant garlic cloves 15 cm from the tomato stem base in autumn for spring protection, or as established transplants alongside spring-planted tomatoes.

Mint's menthol and pulegone volatiles repel aphids and flea beetles through olfactory disruption — but mint must be grown in a sunken pot to prevent its aggressive rhizomes from invading tomato root space. Position the pot so mint foliage surrounds the tomato stem without the roots competing underground.

Chives release allyl sulphide volatiles that deter aphids from landing on tomato foliage by masking the plant's attractive scent cues. Their compact size makes them ideal for underplanting — set chives 20 cm from tomato stems where they'll also attract early pollinators with their purple flowers.

Oregano's dense volatile oil profile — dominated by carvacrol and thymol — creates an aromatic barrier that repels spider mites and cabbage moths while its small flowers provide a continuous nectar source for hoverflies and parasitic wasps. Let it sprawl at the base of tomato cages rather than trimming it back, maximising the protective volatile cloud.

Celery and tomatoes are compatible neighbours with complementary root depths — celery's shallow roots occupy the top 20 cm of soil while tomato roots extend much deeper, so the two crops don't compete significantly for water or nutrients. Celery also attracts beneficial insects with its umbel flowers if allowed to bolt.

Tomatoes release solanine-related compounds that repel asparagus beetle (Crioceris asparagi), while asparagus roots secrete a substance toxic to Trichodorus nematodes that would otherwise attack tomato roots — a genuine two-way chemical defence. Plant tomatoes at the edge of the permanent asparagus bed rather than in the crown zone to avoid disturbing the crowns.

Tomatoes and potatoes are both solanaceous crops that share the same devastating pathogen, Phytophthora infestans (late blight) — spores spread rapidly on wind and rain splash between the two, and infection in one bed can trigger an outbreak in the other within days. Keep them at least 3 m apart and never follow one with the other in rotation for a minimum of 4 years.

The corn earworm (Helicoverpa zea) completes its first generation on corn silk then migrates to tomato fruit as secondary host, effectively doubling infestation pressure when both crops are grown in proximity. Separate them by at least 10 m, or interpose a row of tall sunflowers as a physical barrier to intercept migrating moths.

Tomatoes and brassicas engage in mutual allelopathic inhibition — tomato root exudates suppress brassica germination and growth while brassica glucosinolate breakdown products in the soil can inhibit tomato root development. Keep them at least 1 m apart and avoid composting their residues together.

Broccoli's glucosinolate root exudates break down into isothiocyanates in the soil that inhibit tomato root elongation and can trigger stress responses that reduce fruit yield. Maintain at least 1 m separation and rotate them into different beds each year — never plant tomatoes into ground where brassicas grew the previous season.

Like all brassicas, cauliflower produces glucosinolate root exudates whose breakdown products inhibit tomato root function and can reduce uptake of calcium — a nutrient critical to preventing blossom-end rot in tomatoes. Give them at least 1 m of separation and don't use fresh brassica leaf mulch around tomato plants.

Tomatoes and cucumbers are both heavy feeders that compete aggressively for potassium and magnesium in the root zone, with cucumbers also releasing root exudates that can suppress tomato growth. Keep them at least 60 cm apart in open ground, or in separate containers if space is tight.

Fennel is broadly allelopathic — its roots and decaying foliage release anethole and fenchone compounds that inhibit germination and root development in most garden plants, with tomatoes being particularly sensitive. Keep fennel at least 1 m from any tomato plant and never compost fennel roots or stems near where tomatoes will grow.

Sweet potato and tomato share a susceptibility to Fusarium wilt (Fusarium oxysporum) and several soilborne viral pathogens — growing them together builds up pathogen load in the soil that strikes both crops. Separate them by at least 1.5 m and exclude both from the same bed for at least 3 years in rotation.