Soil fumigants and pest repellents

Nasturtium, false indigo, elderberry, and certain marigolds.

Marigolds: Tagetes minuta repels soil nematodes; T. patula and T. erecta are less effective.

Toby Hemenway recommends planting insect repelling plants in limited quantities because they are not well researched.

Some anecdotal evidence that plantings of sage or scorzona (black salsify)repels carrot fly.

Alliums and nasturtium repel aphids

Tansy repels ants

Basil repels flies and mosquitoes

Marigolds repel Mexican bean beetle

Repel white cabbage butterfly with hyssop, peppermint, rosemary, sage, thyme, and southernwood

Calamus repels mosquitoes

Castor beans to repel moles and mosquitoes (poisonous to humans)