Yes, these plants take up virtually no room at soil level so you can pack them in. They seed well and you'll eventually have seeds coming up all over, but they are no problem and easy to remove.

I'd say you'd need something else at a lower level, as well, though. They're very tall plants, and might look a bit leggy or bare round the base of the pot. They flower in mid-summer onwards, so I think I'd plant something like an annual Osteopermum or two in there with them.

Spritz is right - this plant is great because it takes up very little room at its base, so is very good to plant in between shorter shrubs and perennials, where the wiry, bare stems at the base don't show. Choose something that gets about ten inches high to put in there with them.