In a border. Keep them free of very near neighbours while establishing. After that they can get a bit 'bossy'. See them at GT Dixter!. Mr Lloyd said somewhere, that late in life, he found himself kneeling to get them out of the cracks between the paving stones. I have one clump that is full of itself and 2 others that are thinking about it. They are like Bonariensis,they love crevices to nurture their seeds.