Companion planting, or interplanting, is usually implemented for three reasons: complementary planting, space conservation and to obtain bigger yields.
Companion planting is growing plants, (in the same bed, container or garden), that benefit or complement each other. Some examples of how plants work well together are: shallow and deep rooted plants; short season crops with long season crops; plants that grow upright and those that stay low to the ground; plants that deter pests, (helping to protect plants that are susceptible to insect damage).
This blog lists flowers, fruits, herbs and vegetables that work well together. Compatible plants are in bold, and the incompatible plants are italicized.
pak choi and onions
ASPARAGUS- Basil, carrot, nasturtium, parsley and tomato. Garlic, onion and potato.
BOK CHOY- Beets, celery, onion and potato. Strawberry and tomato.