Are some plants better planted in a group of their fellows than just singly?
My grandmother says some plants are like flocks of birds and do better in a
group. Does anyone know about this?

One more thread for you to do a search on: companion planting, a
practice used by many "organic" gardeners where certain different
types of plants do better when planted along side one another than if
not. Certain insect repellant plants, like marigolds, planted next to
tomatoes supposedly reduce the need for pesticides. This may be what
your grandmother has in mind.