Echinocactus grusonii also known as Barrel Cactus can grow up to 90 cm in height and 180 cm spread. It may offset with advanced age and a few multiples occur even at small sizes.
Stem: Pale green and heavily ribbed.
Ribs: With very numerous areoles.
Radial spines: Yellow spines.
Flowers: Flower are diurnal, vivid yellow 4-5 cm wide
Blooming season: The flowers are produced from end of spring to summer only on larger mature specimens receiving enough full sun.
Echinocactus grusonii are summer-growing and pretty easy plants to cultivate.
Exposure: Outside they need a bright exposure, full sun or half shade in summer if the location is exceedingly hot or bright, inside needs bright light, and some direct sun. It can tolerate moderate shade, and a plant that has been growing in shade should be slowly hardened off before placing it in full sun as the plant will be severely scorched if moved too suddenly from shade into sun.
Frost Tolerance: Light frost protection required for safe cultivation but can tolerate sporadic light frost.