From the designer:

The Plant Pillow is a slight variation on the open top Plant Pocket. In this version, the front and back are the same length with window where you’ll insert a few succulent cuttings.

This is a variation on another pattern by the designer, the “Plant Pocket” (linked in the text). It is basically a knit pillow, filled with soil, and sealed up. Acrylic yarn is recommended to prevent rot, and exact gauge is not necessary. There are braided ties that allow you to display your creation just about anywhere! One of the interesting things about this design is that the plants grow directly out of the knit fabric. Succulents were chosen by the designer because they are hardy, resistant, and easy to grow.

Instructions on how to plant succulents into the finished pillow are here.

For more information on succulent plants, read this.