Getting cacti through the winter is less a matter of tender loving care than intelligent neglect. Cacti native to North America are essentially dormant during the winter. Because they aren’t growing, they need very little water and no fertilizer, and they thrive on cool temperatures. Though cacti are adapted to withstand dry conditions, they absorb moisture rapidly when they’re growing actively — during the spring and summer. During that time, people often underwater them by letting the soil get bone-dry between waterings. Growth is best, however, if the soil dries only partially between waterings. This may mean watering indoor plants every two or three days when they’re actively growing. Plants put outdoors for the summer may need daily watering. In the winter, when growth spots, plants need only a light watering every few weeks to dampen the roots slightly and keep the plants from shriveling. During this time, even once-a-week watering may be too much. Overwatered plants may rot. How you water plants — from the top or the bottom — depends on whether they’re actively growing, what type of growing medium they’re potted in and how thoroughly they fill their pots.
Source: University of Nebraska-Lincoln