Can, and when do you prune yarrow? Just bought some from Lowe's called desert eve and can't find any information on them.
Remove the old flowers as they become brown.
Cut the flower stem back to right above the spot where a branching, or lateral, flower shoots off to the side. Deadheading also prevents yarrow from spreading through your yard, as it is an effective self-seeder when the dead flowers are allowed to dry completely and go to seed.
Cut back yarrow to within 6 inches of the ground after it has finished flowering. In colder climates, cut it back as one of the last chores in your garden before the snow flies. In warmer climates, cut it back in the spring before it begins to bud. Cutting back will promote new growth, giving you a healthier plant with stronger stems.