Buy a Barrel Cactus or seeds from your local nursery, home and garden shop or Internet seed store. Choose a healthy plant that's sturdy and shapely. The miniature Barrel Cactus grows well in containers.
Pot in a small planter or container, for a larger species use a large container. Read the label for the correct size.
Use commercial cactus mix with perlite in a 1 to 1 ratio or mix coarse sand, garden soil and perlite.
Place the plant in a south window or atrium with sun to partial shade.
Water when the soil feels dry 1 inch below the surface.
Fertilize every 4 months with low nitrogen fertilizer during the growing season.