Advice concerning the care of cacti seems very confusing at first. Most cacti, however, fit a particular category based on the care they need. Of course, there are always exceptions, but it seems that whole groups of cacti (even those that need special attention) have very similar needs.
What follows is a discussion of cactus care. The instructions about the needs of the individual types or species are divided into groups, with specifics mentioned when applicable.
1. Standard Care:
This group includes almost all cacti that have been discussed so far. Including all cacti of the genera Mammillaria, Notcactus, parodia, Gymnocalycium, and Echinofossulocactus.
They need a sunny and well-lit location. Only those cacti with a green appearance and sparse spines need protection from direct, harsh and hot sunlight.
Temperatures during the summer months should be between 77°F and 95°F (25-35°C), and between 44°F and 50°F (6-10°C) in the winter.
During their active growing season, the six months from mid-spring to mid-autumn, watering should be thorough and should be done every eighth or tenth day. During the winter months, however, water only very sparingly, since these cacti need to be kept dry.
The amount of moisture necessary in the winter depends upon the temperature. Water less when the plant is in a cooler location, water more when the plant is in a warm location.
These cacti thrive best in a south-east window, less so in a hot south-facing window.
2. Semi-desert Cacti Needing Lots of Heat and Sunshine:
Cacti of this group are easily recognised by their 'white' appearance. They have a white, frosty coat or strong, white or coloured spination.
All of these features indicate that they have adapted to direct sunlight and hot temperatures.
Many of the 'white' Mammillaria and most cacti belonging to the genera Echivnocereus, Astrophytum, Thelocactus, Ferocactus, and Opuntia belong to this group.
These plants like full sun in the summer, with temperatures up to 113°F (45°C). South-facing windows or bay windows receiving full sun are ideal locations for this group.
During the Winter months, many of these plants (Like Echinocereus) tolerate cooler temperatures, while others (like Ferocactus) shouldn't be exposed to temperatures lower than 54°F (12°C).
3. Vigorously Growing Cacti From Low-lying Regions:
Some cacti come from regions with a considerable amount of rainfall and fertile soil. They do not do well with little water and sterile soil.
They're known for their vigorous growth.
Many column cacti, such as the well-known Cereus peruvianus and also those from the genera Cleistocactus, pilosocereus, and Selenicereus, as well as some of the Phyllocacti that come from low-lying areas, belong to this group.
These plants like a lot of light but not necessarily direct, full sun. They also tolerate (even like) winter temperatures up to 68°F (20°C). Watering should be decreased during the winter, but not eliminated.
They like rich, humus soil and frequent watering. Fertilisation can be stronger than is customary for other cacti.
4. Cacti From Higher Regions That Love Fresh Air:
These cacti come from high, mountainous regions. They like lots of light and fresh air, but they won't tolerate high temperature extremes between day and night, and between summer and winter.
Cacti in this group belong to the genre Lobiva, Rebutia, Sulcorebutia, Oreocereus and others, as well as those Echinopsis cacti that grow in high regions (Pseudolobivia).
These plants do poorly behind a hot, south-facing window, but they do wonderfully in a well ventilated hotbed or on a ledge in front of a window, if sufficient protection from rain can be provided. Southeast and Southwest windows are also fine if sufficient fresh air is provided.
Sunlight in higher regions includes a high content of ultraviolet rays. Since ultraviolet light does not penetrate window glass, these cacti appreciate direct sunlight at least now and then.
During the winter months, all watering should cease and temperatures shouldn't exceed 40-43°F (4-6°C). If planted in dry sand, these cacti will even tolerate short, light frost during the night.
Rank and unsightly growth will occur if they are kept in a warm location during the winter, and flower buds will develop only sparsely.
5. Epiphytic Cacti:
These cacti come from tropical forests. The care they need is very different from that needed for other cacti. Their care is much like the care for orchids, which come from the same region.
Included here are cacti from the genus Rhipsalis, as well as Easter and Christmas cacti, and may Phyllocacti. They need a humus and porous soil, and the plants must be continuously moist. The root system should never dry out completely.
In addition, these cacti need a certain amount of humidity. The plants like light, but not full sun. Good locations, therefore, are windows facing north, Northwest, or Northwest, or bay windows. Provide some time outdoors in the shade or a bush tree.
