This guide summarizes the 59 PlantNeighbors pair pages that include Onion. It only marks a pair good or bad when the compiled extension-source facts support that verdict; the rest are treated as ordinary spacing and rotation decisions.
17 documented companions
4 documented incompatibles
38 neutral or undocumented pairs
Documented companions for Onion
Arugula, Beet, bok choy, Broccoli, Brussels Sprouts, Cabbage, Carrot, Cauliflower, Celery, Collards, Kale, Kohlrabi, Mustard Greens, Radish, Rutabaga, Tomato, Turnip.
Pairs to keep apart
Asparagus, Bush Bean, Pea, Pole Bean.
How to use this guide
Start with the sourced pair pages, then adapt the layout to your bed size. Companion planting cannot replace crop rotation, sufficient spacing, water, healthy soil, or scouting for pests.