Caring for Cacti

Cacti are fascinating plants that stand out for their ability to survive extreme conditions and for their enormous variety of shapes, colors, and sizes. Although they are often seen as “indestructible” plants, they require specific care to grow properly, especially in regions with humid climates such as Buenos Aires, where frequent rains, lack of sunlight during winter, and high humidity can negatively affect their health. In this guide, you will find a detailed explanation of every fundamental aspect needed to properly care for a cactus in your home.

Light
Light is a key factor for the healthy development of a cactus. Most species need between 4 and 8 hours of direct sunlight per day, something that is not always easy to achieve indoors.

To compensate for this, try placing them near the brightest windows in the house: north-facing windows receive sun throughout the year, and west-facing windows offer the strongest afternoon sun.

If you notice your cactus stretching, losing thickness, leaning to one side, or turning from a deep green to a paler shade, it is a sign of insufficient light. In these cases, you can rotate the pot every one or two weeks so that growth remains even. If you live in an apartment with limited sunlight, a grow light can be an excellent tool during months with low natural light.

Watering
In humid regions, watering must be even more careful than in dry climates. The environmental humidity of Buenos Aires makes the soil dry much more slowly, especially in winter or during rainy days. For this reason, it is better not to water “every certain number of days,” but only when the soil is completely dry. You can check this by inserting a wooden stick deep into the soil or by lifting the pot to feel if it is too heavy.

In spring and summer, a cactus in Buenos Aires may need watering every 15 to 25 days (depending on pot size, ventilation, and the amount of sunlight it receives). In autumn and winter, especially between May and August, watering should be drastically reduced: many people water only once a month or even once every six weeks, because the humidity keeps the substrate moist much longer.

It is essential to avoid water accumulating in the saucer beneath the pot, as this creates an ideal environment for fungi.

Substrate
Substrate is one of the most important factors for people living in humid environments. Cacti require a highly draining mix to prevent water retention around the roots. In Buenos Aires, the ideal substrate contains a higher proportion of mineral components than in other regions.

A recommended mix is:

40% loose universal potting soil
30% coarse sand or washed river sand
20% perlite
10% pumice stone, volcanic gravel, or fine gravel

This type of mix allows water to drain almost immediately and keeps the soil well aerated, preventing moisture buildup during rainy or foggy days. Avoid compact black soil or common “indoor plant” substrates, as they hold too much moisture.

Temperature
Although cacti prefer warm temperatures between 20 °C and 30 °C, they tolerate humid climates throughout the year as long as they are not exposed to frost or intense cold. What affects them most is not the temperature itself, but the combination of cold and humidity, which encourages fungi and rot. In autumn and winter, it is recommended to keep them in places protected from rain and with good ventilation.

If you keep them on open balconies, it is a good idea to move them closer to the wall or place them under a roof when temperatures drop or when it rains for several days in a row.

Fertilization
In humid cities, fertilization is still important for balanced growth. During spring and summer, apply a cactus-specific fertilizer once a month. These fertilizers contain low nitrogen levels, preventing soft growth, which can be more susceptible to fungi. Suspend fertilization during autumn and winter, as cacti enter a resting phase and do not use nutrients in the same way.

Appropriate pot
The pot is essential in humid climates. Clay or terracotta pots are ideal because they absorb part of the moisture from the substrate and allow faster evaporation. Plastic pots retain moisture for longer and can favor fungal growth in humid seasons. Regardless of the material, make sure the pot has large drainage holes and, if possible, elevate it a few centimeters above the saucer so water does not remain in constant contact with the base.

Common pests
The humidity of Buenos Aires encourages the appearance of mealybugs, mites, and fungi. Mealybugs are very common and can be identified by small white cotton-like clusters between the ribs, at the base of spines, or on the substrate surface. Red spider mites can appear in very dry and hot environments, while fungi thrive in humid, poorly ventilated conditions.

To keep pests under control:

Check your cacti every one or two weeks.
Avoid spraying them with water or direct humidity.
Ensure the substrate does not remain wet for several days.
Apply isopropyl alcohol with a cotton swab to visible mealybugs.
If the problem persists, use cactus-specific insecticides or antifungal products, always following the instructions.

Cacti are noble plants that easily adapt to different environments, even to humid climates such as Buenos Aires, as long as they receive the proper care. With a good combination of light, controlled watering, airy substrate, and pest prevention, they can stay healthy for many years.

Understanding their needs will allow you to enjoy their beauty and vitality throughout the year.

Sources
Kiesling, R. "The genera of Cactaceae of Argentina". Argentine Botanical Society
Quipildor, V. "An analysis of the columnar cactus Echinopsis terscheckii". CONICET Institutional Repository
Barbarich, M. F. "Multidisciplinary study of cardones (Trichocereus spp.)". UBA Digital Library
Andrade, J. L. "The crassulacean acid metabolism". UNNE Repository
Domínguez, F. M., et al. "Studies on the effects of pH, stomatal density, acid ..." Dialnet