The makeup of the growing medium depends upon the plants you choose to grow, as the media should have last to match the life expectancy of the green wall plant.

Annual plants require a good potting soil mix.
For Annuals, Vegetables, Small Fruits, and Herbs

Plants are expected to be used for one full year need a good quality peat-based or coconut fiber-based potting soil. These are available at local garden centers.

Perennials need a good potting soil with perlite, pumice or pine bark.
For Perennials, Vines and Tropicals

Plants that are expected to last for 3 to 5 years before dividing, use a good quality potting soil, with perlite or pumice and/or composted pine bark. Such potting soils will tend to decompose less.

Succulents may last decades without repotting, so need a highly inorganic growing media.
For Succulent Plants

Plants that can last decades without repotting, succulents need a good quality mix, typical of one marketed for rock gardening. The unique quality of such mixes is that they have a high mineral content (e.g. perlite, pumice, or expanded shale) and less organic matter, and therefore do not decompose over time.