Mammillaria

Mammillaria is a genus of 147 accepted species in the cactus family (Cactaceae) and many are popular to grow as houseplants. The species in this genus are native to the Central and Southwestern United States to Colombia and the Caribbean to Venezuela. The plants may be spherical or cylindrical and have colorful flowers. The genus name, Mammillaria, is derived from the Latin word, mammilla, meaning "nipple" and referencing the appearance of the tubercles on the stem.

These plants grow best in full sun or bright direct light and appreciate some afternoon shade in hot weather. Grow them in a well-drained cactus mix with added grit or coarse sand to encourage adequate drainage. They are tough plants and can tolerate a variety of conditions. These plants thrive in temperatures between 70 and 80 degrees Fahrenheit. During the winter, these plants go dormant and then prefer temperatures between 45 to 55 degrees Fahrenheit. This will encourage flowering in the spring. They are cold-intolerant and should be brought indoors during the winter months. Allow the soil to completely dry out between waterings, but during its dormant period suspend all watering. Repotting may be required every 2 to 3 years. Seeds and dividing offsets or pups are the easiest way to propagate these plants. 

Mammillarias are small and may be globose or short cylinder-like stems. They may occur solitary or form clumps. Some species form mounds of stems that measure over 3 feet in diameter. The stems vary in size depending on the species and can measure 0.4 to 16 inches tall and  0.4 to  8 inches wide. Each species has tubercles with areoles and spines. The spines may be straight or hooked. Some species are woolly and hairy. The flowers are funnel-shaped, range in colors of white, green, yellow, pink, or red and usually have a dark-colored mid-stripe. The flowers often form a ring or halo around the top of the plant. Blooms occur in the second year of growth, and the season of flowering is dependent on the species. The fruits are usually red and club-shaped, while others may be white, yellow, green, or magenta. Some species produce edible fruits while others have a very unpleasant taste.

Mammillarias are non-toxic to humans and pets, low maintenance, and easy to grow; however, the spines are sharp and may cause injury. Unfortunately, some of these plants are endangered due to their popularity from over-collection or poaching.

There are many species to choose from that have a variety of shapes, sizes, and flower colors. Consider one or more of the species as a houseplant or a container plant due to their compact size and slow growth rate. In warmer climates, they can be planted in a rock garden, border, or succulent bed. 

Quick ID Hints:

• Small size and rounded or cylindrical shape
• Tubercles (rounded projections) arranged in a spiral pattern
• Small, funnel-shaped flowers that form a halo around the top

Insects, Diseases, and Other Plant Problems:  May be susceptible to mealybugs spider mites, and scale insects. Bacterial or fungal diseases may result from overwatering or poor air circulation. 

VIDEO Created by Laura Barth for "Houseplants, Succulents, and Cacti", a plant identification course offered in partnership with Longwood Gardens.