Cactus watering

There are big differences about watering needs within the Cactus family. Needs change depending of the area from each species come. As a general rule, with the exception of epiphytic species, waterings must be moderate. However, we must not think that because cactus are xerofitic plants, they do not need water at all. Although most cactus can stand really long drought periods, these plants needs water during all the growing season. Moderate watering is the key with cactus. We called by this name the systematic watering (frequency and dose) that satisfies most of cactus, although other species have special needs. By instance: if we water a plant from the Pyrrhocactus genus, as we water species with average needs, The poor Pyrrhocactus would be destroyed quickly, since this plant requires many less watering than most of cactus. On the other hand, epiphytic cactus need constant humidity in the soil the whole year.
It is difficult to make a cactus watering calendar, since the frequency of waterings depends on the type soil used, temperature and humidity of each zone. However, if we are using standard soil mix, and for a climate like the one of Buenos Aires, we can use the following directions, adapting to the special circumstances in each case.
When the spring begins and all risk of sudden changes of the temperature have gone, and the plant starts to grow again, then is time to start watering very slowly with a certain frequency (once every 8 or 10 days). When the plant is in active growth we can increase the watering frequency progressively until the warmer months, in which we can water every 3 or 7 days according to zones. There will be a period in the middle of summer (when nights are to hot) when cactus will grow a little or don't do it at all. We must adapt watering to this circumstance. When warm starts to go, it is time to reduce waterings (once every 8 or 10 days), so we can induce the plants to dormancy. It is advisable not to water at all during winter. Nevertheless, we can spray the plants once in a while.
It is important to know than with temperatures below 10º C, we must not water cactus since rotting risk is high.
In growing cactus is better one good watering that dampens all soil once in a while, than ten superficial waterings which do not reach the absorbent hairs of the root.
Another good practice is to let dry the soil completely between watering.
Except the species with hair, all cactus like to be sprayed with water once in a while.
Best time for waterings are, the last hours of afternoon when is warm, and the first hours in the morning when is temperate.