Gymnocalycium Denudatum | A Tiny, Weird Looking Cactus |

Gymnocalycium denudatum is an endemic plant to Paraguay, Uruguay and to Brazil. This is known as spider cactus in common. 

Gymnocalycium denudatum is renowned for its green stem which tends to take a globular shape. Further their brown spines are also one of the main highlights of them. 

This cactus easy maintenance makes them a perfect choice for the fresher for the  succulent gardeners. So, if you are eager to learn about these plants, keep reading this article. 

Gymnocalycium Denudatum

How do I identify Gymnocalycium denudatum?

Gymnocalycium denudatum cactus is a tiny globular cactus. They would be usually unbranched, and their body would be glossy dark green in color. 

They would consist of round ribs as well. Their stem forms solitary and it would be about 2-3 cm in height. Further it would be 6-8 cm in width. 

They would consist of about 5 – 8 ribs. Those ribs would comprise poorly developed tubercles.  

Gymnocalycium denudatum cactus areoles are round and slightly wooly and they would form 1-2 cm apart.

If I elaborate further on their spines, they would be all radials and tend to look like spiders. They are harmless for humans, and they would be about 1-1. 5 cm in length. 

Those spines would be either white or pale rose. Besides, they would tend to take an awl shape.

Gymnocalycium denudatum cactus spines are slender and form in an upward manner. In addition to these features, this cactus produce flowers which tend to take a cream white color. 

Those blooms would be 5 cm in length and 7 cm in width. Spring and summer are their flowering seasons. They further develop a fruit which is oblong and green in color.

Growth rate

Gymnocalycium denudatum cactus are a somewhat rapid growing cactus type. Further they are easily flowering species as well.

One look care guide

Botanical NameGymnocalycium denudatum 
Common NameSpider cactus
Plant TypeCactus
Mature SizeMaximum height of 10 cm ( 4 inches ). 15 cm ( 6 inches ) in width. 
Sun ExposureFull sunlight to light shade
Soil TypeWell-draining
Soil pHLow pH.
Bloom TimeSpring summer
Flower Colorcream white color
Hardiness ZonesUSDA hardiness zones 9b-11b- 3.9 degrees Celsius  ( 25 degrees Fahrenheit ).
Native AreaParaguay, Uruguay and Brazil.
ToxicityNon toxic
Average price 8 USD
Gymnocalycium Denudatum

How do you take care of  Gymnocalycium denudatum?

Light Requirement

Gymnocalycium denudatum cactus can stand the extreme bright sunlight. Having said that, they would still prefer to have filtered sunlight during an intense afternoon time. 

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Literally morning direct bright sunlight as well as some shade during intense hottest days would be optimal for them. 

They would turn bronze when they get bright sunlight. Further it would be beneficial for the flowering process of the Gymnocalycium denudatum cactus. 

Moreover, it would encourage spine production as well. Having said that, the exposure for intense sunlight for extended periods would scorch the plants and even result in stunt growth. 

Temperature and humidity

Gymnocalycium denudatum cactus could resist light frost if you had kept them dry prior to that. They are in fact cold hardy to some extent. Having said that, refrain from exposing them to freezing temperatures.

Is it cold hardy?

Gymnocalycium denudatum cactus are cold hardy up to -2 degrees Celsius  for short periods.

USDA Hardiness Zone

Gymnocalycium denudatum cactus prefer to grow in  USDA hardiness zones 9b-11b- 3.9 degrees Celsius  ( 25 degrees Fahrenheit ).

Watering Requirement 

Gymnocalycium denudatum cactus thrive well with moderate watering during summer. However, ensure that you do not over water them as these plants are prone towards root rot. 

It is important that you water them properly as it is very important when looking after these plants well.  Literally you should never leave them exposed to waterlogged conditions. 

Instead, excess moisture should drain through the draining holes. When watering , ensure that you soak these plants well with a thorough watering and allow them to dry after that. 

Reduce watering the Gymnocalycium denudatum cactus during winter as they should be kept during the cooler times.

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Gymnocalycium Denudatum

Soil Requirement Type / pH.

Gymnocalycium denudatum cactus will perform well if you provide a soil mix which is high in porosity. Best is to use a standard cactus soil mix for them. 

A low pH. Compost soils mix would work well with them. So nor grow them in substrates which have high components of limestone. 

It is important that your selected soil mix is fast draining and well aerating as those are two crucial factors which you need to consider when selecting a right soil mix to grow the Gymnocalycium denudatum cactus.

Pot size Potting and Repotting

Gymnocalycium denudatum cactus would prefer to have a pot which consists of a draining hole. That will allow the excess moisture to drain away from the pot

Moreover, consider growing them in an unglazed terracotta pot as those would be optimal for the Gymnocalycium denudatum cactus healthy growth. 

When it comes to repotting, I recommend doing it every other year as they need plenty of space to develop their roots.

If you spot the plants have outgrown from the pots, you need to consider repotting them too.

Where to Plant

Gymnocalycium denudatum cactus have strong demand when it comes to sunlight. Hence, if you grow them in your garden, ensure that the selected spot in your garden gets adequate sunlight. 

As aforesaid some direct bright morning sunlight and partial shade during afternoon hours would be ideal for them. 

Gymnocalycium denudatum cactus prefer a warm climate. Hence if you live somewhere where the temperature gets much colder, you can grow them as indoor plants. 

Further if you wish to grow them a potted plant, ensure that you grow them in a pot which has a good porosity.

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Fertilizer and time of year

A fertilizer which has a high potassium content would be quite useful for the Gymnocalycium denudatum cactus’s optimal growth. You may feed them during spring and summer as those are their active growing seasons.


Gymnocalycium denudatum cactus blossoms with some attractive  flowers during spring. They would produce white flowers and it would be a treat to watch them in full blossom.

Gymnocalycium Denudatum


Gymnocalycium denudatum cactus are winter dormant plants.


Gymnocalycium denudatum cactus are nontoxic plants.

Common bugs and illnesses

Gymnocalycium denudatum cacti are prone to insect attacks. Having said that, if you provide the optimal growing conditions, they will grow pest free

If you had grown them in a mineral potting mix which has a good aeration, mostly your plants will be problem  free. However, pests such as red spiders’ mealybug scales would be troublesome for them. 

To briefly explain on them, mealybugs would usually form aerial and into the new growths of the plants. Further they may develop underground as well.

Gymnocalycium denudatum cactus could be a victim of Scales very rarely.  If you had watered the cactus well and if you had provided a good aeration, they would hardly suffer with rot. 

Further, if the rot gets severe , even the fungicides would be effective to overcome that situation.  

Special Care tips

Gymnocalycium denudatum spines are almost harmful. However, ensure that you are extra cautious when handling them.

How to propagate Gymnocalycium denudatum

You may propagate the Gymnocalycium denudatum cactus by its seeds. You can directly sow them in a well-draining soil layer. 

It would take about 7-14 days for them to germinate. The ideal temperature during this process should be 21-27 degrees Celsius and you need to conduct this  in spring. 

You can spot them developing roots within 1-2 weeks’ time. Ensure that you protect the specimen from full sunlight. Further provide good ventilation as well.


To wrap up, I hope this article was useful for you and that it gave a broader knowledge of how you should look after them well. 

If you make sure that you fulfill their basic necessities , they will thrive well and flourish as beautiful plants. So, hurry up, grab your Gymnocalycium denudatum cactus and start growing them !

Credit to : Алекс Кактус
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About author

I’m Dr. Chamika, As a hobby love talking about plants and showing you that taking care of indoor plants. My website is knowledge I’ve learned over the years and continue to learn about growing succulents. If you’re a succulent lover, then you have come to the correct place.