How often should I water it?

Water only when the soil has dried out completely, usually every two to three weeks in summer and much less in winter.

Does it need direct sun?

Yes, it thrives in bright, direct sunlight for most of the day.

Plant guide

Thimble Cactus.

Mammillaria gracilis fragilis

Pronounced mam-mi-LAIR-ee-uh VET-yoo-luh

Also known as Mammillaria gracilis fragilis

Mammillaria vetula — Photo by John Rusk (CC BY) via iNaturalist

The thimble cactus is a charming, small succulent that forms dense clusters of tiny, cylindrical stems. It is a favorite for collectors because it stays compact and produces lovely little flowers. You will find it is quite resilient if you give it plenty of sun.

Another photo of Thimble Cactus — Photo by Naelin (CC BY) via iNaturalist

At a glance

Care level: Easy
Plant type: Succulent
Light: Full sun
Indoor light: Direct sun
Water: Every 14 to 21 days
Mature size: 4 inches tall
Growth rate: Slow
Hardiness: USDA 9 to 11
Bloom time: Late winter to mid spring

Care

Keep this cactus in a spot with intense light to prevent it from stretching out. Let the soil dry out completely between waterings, and watch for shriveling stems as a sign it needs a drink. Ensure the pot has excellent drainage to keep the roots happy.

Watering: Water only when the soil is completely dry throughout the pot.
Feeding: Use a balanced cactus fertilizer during the active growing season.
Pruning: Only remove dead or damaged stems with sterile shears.
Repotting: Repot only when the cluster has completely outgrown its current container.
Soil: Well draining cactus mix
Soil pH: 6.0 to 7.5
Temperature: 5 to 35°C
Humidity: 10 to 40%
Drought tolerance: High
Lifespan: Perennial, typically 10 to 20 years
Deer and rabbits: High

Signs it needs repotting

The plant has filled the entire pot with offsets.
Water runs straight through the pot without soaking in.
The plant has stopped growing during the active season.

Safety

People: This plant is not considered toxic to humans.
Pets: This plant is generally considered non-toxic to cats and dogs.
Children: Keep this plant out of reach of children due to the sharp spines that can easily pierce delicate skin.
Contact allergens: The sharp spines can cause mechanical skin irritation or puncture wounds if handled without gloves.
Airborne allergens: There are no known respiratory allergens associated with this plant.
Edibility: While the fruit is technically edible, it is not commonly consumed and lacks significant culinary value.

How to identify it

Small cylindrical stems in clusters
Dense white radial spines
Tiny cream or yellow flowers
Offsets readily from the base

Height: 0.05 to 0.15m
Spread: 0.1 to 0.3m
Leaves: green, evergreen
Flowers: yellow, cream, 1 to 2cm
Fruit: red, Summer

Problems to watch for

MealybugsCommon
Root RotCommon
Scale InsectsUncommon
Spider MitesUncommon

By symptom

Plant problems by symptom

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Growing it

Propagation: cuttings, division, seed
When to plant: spring, summer
Overwintering: Keep the plant in a cool, dry location and withhold water almost entirely to encourage dormancy. Ensure it stays above freezing temperatures.
In containers: This cactus is excellent for containers, provided the pot has drainage holes and is only slightly larger than the root ball.

Stem cuttings

Carefully remove a small offset from the main cluster using a clean, sharp knife.
Allow the cut end to callous over in a dry, shaded spot for several days.
Place the calloused cutting on top of well draining cactus soil.
Keep the soil barely moist until roots begin to form.

Group this cactus with other desert plants that require excellent drainage and minimal water to ensure they all thrive together.

Grows well with

Echeveria · They share similar requirements for bright light and infrequent watering.
Aloe · These succulents provide a nice structural contrast to the rounded form of the cactus.

Similar species

Mammillaria elongata · It has a similar clumping habit but with more elongated, finger like stems.

Science

Family: Cactaceae
Genus: Mammillaria
Order: Caryophyllales
Class: Magnoliopsida
Native range: Central Mexico
Conservation: This species is not currently listed as endangered in the wild.

It grows in rocky, well drained soils in arid environments, relying on its water storing stems to survive long droughts.

Value to wildlife: nectar source
Pollinators: bees
Uses: ornamental, container plant, rock garden

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 8/9
Temperature: 7/9
Moisture: 2/9
Nutrients: 2/9

Taxonomy resolved against GBIF.

Questions people ask

How often should I water it?: Water only when the soil has dried out completely, usually every two to three weeks in summer and much less in winter.
Does it need direct sun?: Yes, it thrives in bright, direct sunlight for most of the day.

Where the name comes from

The genus name Mammillaria comes from the Latin word mammilla, referring to the nipple like tubercles on the plant, while the species name vetula means old.

Good to know

The name gracilis means slender in Latin.
It is often called the Thimble Cactus because of its small, cylindrical stems.
It is a very popular choice for beginners because it is quite forgiving.
The flowers often form a ring around the top of the stems.

Also in

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This guide was generated with AI on September 26, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.