I'd rather have roses on my table than diamonds on my neck.
Anise is a host plant for predatory wasps that kill aphids. Both coriander and anise deter aphids.
Artemisia includes many varieties that have insecticidal properties. Plant a species of Artemisia, like wormwood or tarragon, to deter the hated slug. The strong scent of this shrub will help keep away the hated slug, probably the dahlia's most feared pest. If you grow as a border around your garden, wormwood will deter animals as well. People often hate to kill slugs but, they can wipe out an entire garden overnight.
They're hardy annuals and are famous for growing almost anywhere. It repels black aphids and its leaves have a delicious peppery flavor that you can add to your salads. Their colorful flowers are also edible and make beautiful and delicious garnishes for soups, salads, deserts, fruit trays, etc. They're beautiful as a garnish. Remember to tell folks that they're actually edible. Most varieties will do well in partial shade. Great for bordering, these low-growing plants will provide a colorful ground cover around or next to their taller neighbors.
A member of the genus salvia, the flowering sage grows spikes or towers of flowers (look like rock candy) that attract hummingbirds and butterflies. Not only will they add beauty, but the butterflies and hummingbirds will eat aphids and harmful beetles! Salvia grows in clumps and requires full sun, so don't plant too close to the dahlias. The flowering sage come in different colors (red, white, blue, violet, and pink) and sizes (18 inches to 5 feet) so you can match appropriately with your dahlias.