Cacti are succulent plants that live in dry areas (xeric environments). They can survive long periods of drought (a lack of water). Cacti have many adaptations that allow them to live in dry areas; these adaptations let the plant collect water efficiently, store it for long periods of time, and conserve it (minimizing water loss from evaporation). Cacti have a thick, hard-walled, succulent stem - when it rains, water is stored in the stem. The stems are photosynthetic, green, and fleshy. The inside of the stem is either spongy or hollow (depending on the cactus). A thick, waxy coating keeps the water inside the cactus from evaporating. Many cacti have very long, fibrous roots, which absorb moisture from the soil. Some, like ball cacti, have shorter, more compact roots that absorb dew water that falls off the cactus.
Instead of leaves, most cacti have spines or scales (which are modified leaves). These spines and scales do not lose water through evaporation (unlike regular leaves, which lose a lot of water). The spines protect the cactus from predators (animals that would like to eat the cactus to obtain food and/or water). Areoles are circular clusters of spines on a cactus. Flowers bud at an areole and new stems branch from an areole.
These are some of the common cactus varieties
Hedgehog Cactus: They have several one to two inch long spines on them thus the common name. Native to Central Mexico to the Western United States, there are about 50 cactus species common named Hedgehog Cactus.
Blossfeldia liliputana: It is the smallest cactus species. These cacti are native to South America and produce small, beautiful looking pink flowers which are about 5 to 7 mm in diameter.Star cactus:
Barrel Cactus: Native Americans used this cactus as a cooking pot. It is also known as Candy Barrel Cactus as its pulp has been used to make cactus candy.
Saguaro Cactus: The tallest cactus that grows very slowly. It produces edible fruit that ripens in June, this fruit is highly prized by locals. A single fruit can contain up to 4,000 seeds.
Star Cactus: It is a small, spineless cactus with a circular body that grows about 2-6 inches in diameter and about 1-2 inches tall. They bloom from March to May and fruits from April through June.
Prickly Pear: A very common cactus, also known as tuna nopal or paddle cactus.
Organ Pipe Cactus: It is considered the second tallest cactus after Saguaro Cactus, growing as tall as 23 feet. It produces edible fruits which lose their spines upon maturity and display an edible red pulp. This fruit is a food source for native Americans.
Light: Strong light is essential for healthy cacti, especially in the winter. Some species may scorch in direct summer sun if they haven't been hardened off first.
Temperature: During the active growth period, cacti prefer hot, dry temperatures, ranging from 70ºF to more than 80ºF. In the winter, the plants prefer a cooler period, down to 55ºF. In their desert habitats, many cacti are accustomed to very chilly nights. However, protect them from very cold winter drafts.
Water: In the spring and summer, when the plant is actively growing and/or blooming, water whenever the compost begins to dry. During these waterings, make sure the plant is thoroughly watered. During the winter rest period, nearly cease watering. Only water if the plant begins to shrivel.
Potting Soils and Repotting: Pot into a fast-draining cacti mix. If one is not available, amend regular potting soil with inorganic agents like perlite to increase drainage and aeration. Cacti are generally slow-growing plants and will rarely need repotting. Also, remember that many species of cacti will bloom better when they are slightly underpotted.
Fertilizer: Use a cacti fertilizer during the growing season. Some growers have poor results with standard fertilizers, so it's probably worth it to seek out a specialized cacti fertilizer.
Common Problems: The most common mistake with desert cacti is overwatering in the winter, which will cause rot either at the base of the plant or at the tips of the growing areas. If the rot is advanced, it might be necessary to start new plants from cuttings or discard the whole plant. Cacti are also susceptible to pests include mealy bugs and mites.