Like other succulent plants, cacti store water and can draw upon their own reserves during water shortages. All cacti are characterized by their seed and flower structure, but despite this botanical commonality, they can take on many shapes, sizes and temperaments. In general, these robust plants should be kept dry, well-lit and at a temperature no more than 41 degrees Fahrenheit to 46 degrees Fahrenheit in the winter (5 to 7.7 degrees Celsius). If natural light is inadequate, purchase a grow-lamp from a plant store or have a professional install a high-intensity mercury lamp. Artificial light helps cacti acclimate to stronger light come springtime. If it's too dark or too warm during this resting season, plant tissue goes limp and becomes susceptible to infectious diseases. To keep cacti outdoors during excessively wet or cold weather, ensure they stay dry with a waterproof tarp or covering. Some can actually endure severe frosts if kept dry this way. Once the danger of frost passes, you can plant cacti outdoors.