Marigolds are a good example. They are often used to repel whiteflies and some aphids from vegetable and other plants. Although it is true that whiteflies do not like marigolds, mites and slugs will search high and low for a good marigold patch to enjoy. So, while repelling whiteflies, you may invite all the local slugs and mites into the area. Another concern with companion planting is the room it requires, he adds.
Weeds are enough.
Garlic and onions are fine in their place, but not spread all over the garden. Most vegetables, especially beets, tomatoes, cabbages and a few others, grow better and healthier when they do not have to compete with plants growing close by, even if they are companions. My last concern is how complicated gardening becomes when trying to control one simple pest, Goodspeed says. I have seen matrix charts of vegetable gardens developed to determine plant spacing and the location of companion plants. They are more complicated than tax forms.