The whole window will have a one foot wide window sill. I will have to show you the place to get a good idea of things. Basil planted in teacups for the kitchen, cheap and pretty teacups planted with fresh herbs on the window sill.
Build this trellis and raised garden box combination. Cucumber, snap peas, green beans, tomatoes… ah, just think about that fresh organic food you can grow in a small area! Another huge advantage is that harvesting is a breeze.