Here’s where the irony kicks in. You want to kill ants, so you have to feed them. Use a commercial ant bait gel or make your own mix of borax and sugar water (1:3 ratio). Put the bait in a small lid or bottle cap near the ant trail, but away from the plants you love.
Why does this work? The ants take the sweet poison back to the nest and share it. They die at home, not on your hydrangeas. Pro tip: Don't spray Raid on the trail. If you kill the scouts, the colony never gets the poisoned food. Let the little delivery service do its job for a few days. It feels weird, I know. But it works.
The Three Sisters Planting Method: A Beautifully Balanced Garden