I planted some last year, and it's spread a bit, popping up here and there. It looks nice now but I'm slightly concerned it will become invasive in my narrow (50cm) wide border. Dryish rich and free draining soil. Should I pull it out? I want to plant some Sedums in the same bed so am delaying planting them until I've made my mind up!
What about lifting a portion out of the ground and confining it to a small trough or something similar , the get rid of the rest from your border ?