Plants can be like people…both require food, water, light, and air. Also, plants have likes and dislikes of their neighbors and companions.
Some plants can provide special nutrients needed by neighboring plants, or even the root system of a certain plant helps to loosen the soil.
Some plants like, marigolds, are bug repellents while other plants, like parsley and yarrow, attract beneficial insects.
Being knowledgeable about of this natural interaction gives gardeners a head start in combating pests in the garden naturally.
Here’s a rundown on some of the plants that do and don’t grow together well.
Roses like garlic, but dislike boxwood: tomatoes like basil; dislikes rue; cucumbers dislike sage; carrots dislike dill; most plants dislike fennel.
Alliums are good with most any plant because it deters insects, but peas and beans are inhibited by them. Naturstiums are good bug repellents and are benefical to radishes and apple trees.
Yarrow attracts lady bugs and is beneficial to surrounding plants, but wormwood inhibits plant neighbors with toxic root system.
This info and more is in my favorite herbal gardening book