This beautiful, small cactus has a cylindrical green body covered in interwoven white spines. “Thimble Cactus” grows in clusters, and propagates very easily. You can expect to see tiny cream-colored flowers in cooler months.Native to Central Mexico, thimble cactus (Mammillaria gracilis) is suitable for growing outdoors in USDA plant hardiness zones 9 through 11. Although it tolerates drought and extreme heat, it won’t survive long if temperatures drop below 25 F. (-4 C.). This slow-growing Mammillaria cactus is a great choice for xeriscaping or rock gardens, but it also performs well in a container, making an excellent houseplant. It is generally very easy to grow.