I have a very narrow border alongside a path that leads up to a front door. East facing. I'd like to grow a row of just one plant there, for impact, but it needs to be something that won't spread out too much - height is fine, but I don't want to be climbing through it on a daily basis. What would be a good plant to try? Would love some bright colour, and have thought of Crocosmia but not sure if it will get too bushy. The soil is clay. Thanks for any suggestions!