A great way to naturally increase yield and make your vegetable plants stronger against pests is to plant them with herbs and/or other flowering plants that repel pests. This is companion planting.
Basil's strong fragrance repels unwanted pests. They are usually planted with tomatoes.
Chives are great against carrot flies.
Dill & fennel repels aphids.
Marigolds drives away many bugs, mites and unwanted insects.
Rosemary is great against cabbage moths & carrot flies.
Thyme keeps cabbage worms at bay.

You may get Awapuni Herb Seedlings here.

More planting guides here.