Companion planting guide › Garlic and onions near aphid-prone crops

Garlic and onions near aphid-prone crops: does it work?

Promising Some peer-reviewed or extension evidence, but limited, conditional or mixed.

Several studies found garlic or onion intercrops delayed or reduced aphids on neighboring crops, likely by masking host odor.

1. Ben-Issa R., Gomez L., Gautier H. (2017). Companion Plants for Aphid Pest Management. Insects 8(4):112 (peer-reviewed review).

Mechanism

Volatile compounds mask the host plant's odor or repel aphids.

What the research found

• Garlic planted a month before tobacco delayed winged green peach aphids and reduced their abundance over two years (Lai et al., reviewed in Ben-Issa et al. 2017).
• Onion/garlic intercrops reduced aphids on cabbage and mustard in other studies listed in the same review.

Caveats

Results vary by crop, aphid species and timing. Little garden-scale US data. No good evidence for the popular garlic-under-roses claim specifically.