How to Grow Garlic

Garlic produces allicin and diallyl disulphide volatile compounds that repel red spider mites (Tetranychus urticae) — a major tomato pest — and may also deter aphids and whitefly. Plant garlic cloves 15–20 cm from tomato stems; interplanting at transplanting time ensures garlic is established before spider mite season peaks in warm weather.

Garlic's allicin volatiles create an olfactory barrier that disrupts the host-finding behaviour of aphids — particularly Myzus persicae — that colonise pepper plants, reducing establishment rates. Plant a ring of garlic around each pepper, or interplant alternate rows, ensuring cloves go in at the same time as pepper transplants.

Garlic's sulphur compounds may help deter aphids and fungal pathogens that affect beetroot, while both crops have modest, non-competing root systems that coexist comfortably in the same bed. Their offset harvest times — garlic in early summer, beetroot mid to late season — also make them practical bed-mates for space efficiency.

Garlic's allyl sulphide volatiles mask the volatile carrot root fly (Psila rosae) host-cues that carrot fly uses to locate its egg-laying sites, significantly reducing larval tunnelling damage. Interplant garlic cloves between carrot rows at a 1:3 ratio; the scent barrier is most effective when garlic is actively growing and releasing fresh volatiles.

Garlic's sulphur volatiles deter aphids, spider mites, and botrytis-spreading insects that commonly target strawberry plants, while allicin may have some fungistatic effect on Botrytis cinerea spore germination. Plant garlic between every third strawberry plant, or as a perimeter row around the strawberry bed.

Garlic produces allicin and related thiosulphinates that inhibit Rhizobium bacteria in broad bean root nodules, directly suppressing nitrogen fixation and stunting plant growth. Keep garlic at least 50 cm from broad beans — even upwind separation helps since soil-borne leachates can travel some distance.

Garlic's thiosulphinate root exudates inhibit Rhizobium leguminosarum, the specific bacteria that fix nitrogen for peas, reducing nodule formation and cutting the nitrogen benefit peas provide to themselves and the surrounding soil. Maintain at least 50 cm separation; in small plots, grow garlic in a separate bed entirely.

Garlic exudes allicin-derived thiosulphinates into the soil that bind to and deactivate Rhizobium bacteria in runner bean root nodules, blocking nitrogen fixation and reducing plant vigour. Keep a minimum 50 cm gap and avoid planting garlic in the same bed the season before runner beans, as residues can persist in soil.

Allium root exudates — particularly thiosulphinates and fructooligosaccharides — have been shown to inhibit the growth of asparagus crowns and reduce spear emergence in the critical establishment years. Since asparagus is a perennial that requires 2–3 years to mature, even moderate suppression compounds over time; keep alliums at least 60 cm away from asparagus beds.

Both garlic and sage produce strong volatile oils that suppress each other's growth when planted nearby. Keep at least 60 cm apart to avoid allelopathic interference.