This is Echeveria ‘Imbricata’ in planter boxes under one of my front windows. Succulents are a great choice for your summer window boxes (or year round window boxes in mild climates like mine). All they need is weekly water and the very occasional cleanup. I wanted a uniform look (and a mass of flowers this time of year), but you can mix succulent types to combine colors and give you some height. Echeveria ‘Imbricata’ is probably my favorite succulent. The rosettes can grow to the size of plates, they can take some shade, hummingbirds love them, and they give you tons of babies. All of these are from a single plant I bought a few years ago.
Here are some large planters with Echeveria and Aeoniums. I love the blue and black tones in the blue planter. The Aeoniums (the black ones) will become tall and branching. If you want to keep them low, just break them off and stick them back in the dirt.