First, start with a simple wooden box and cover it with a sheet of copper. "This will give it that lovely green patina," he says.
Then, after putting down a base of soil, add a spillover plant like a bacopa. But don't get hung up on what your plants are called. "I often tell people buy plants with shapes first, names second," Jamie says.
After the spillover bacopa is in place, Jamie arranges pretty flowers in the box. Here, he uses white volcano phlox and pink geraniums. Then Jamie adds sphagnum moss. This will absorb nutrients in water and keep the soil moist, which is important for flower boxes that are regularly exposed to sunny and windy conditions.
Last, fill in any holes with more soil, and you're ready to hang your summer window box...just don't forget to water the plants.