The terms "cacti" and "succulents" are sometimes confused. All cacti are succulents, which means they are capable of storing water, but not all succulents are cacti. Cacti, of the family Cactaceae, is a wide-ranging group that includes many species. While their U.S. Department of Agriculture plant hardiness zones differ by species, they all developed in low-water environments where the ability to store moisture is an asset.
Aloe (Aloe spp.) is a wide-ranging genus containing about 240 species. The best known of these in the U.S. is aloe vera (Aloe vera), sometimes called medicinal aloe or simply aloe. It is a perennial and is winter hardy in USDA zones 10 through 12. Because it evolved in hot, dry areas, it is well adapted to full sun and low water conditions, so is good for arid gardens or as a neglected container plant.
Yucca plants (Yucca spp.) are succulents that often have trunks. Leaves tend to be leathery rather than fleshy and are overall thinner in appearance than aloes. They adapted to less extreme heat and moisture conditions. Adam’s needle (Yucca filamentosa), for example, is hardy in USDA zones 4 through 8 and enjoys dry to medium moisture levels. Yuccas are known for their dramatic upright flower panicles, which grow above the foliage.
Noted for the rosette shapes that agave (Agave spp.) traditionally assume, these succulents make good specimens and container plants. Their leaves come in a wide range of colors, always arranged circularly around a central point, each leaf containing a spine at the end of it. More than 200 species exist, most of them suited to landscape use. One of the most common is the century plant (Agave attenuata), which is winter hardy in USDA zones 10 through 12.
Sedum (Sedum spp.), also known as stonecrop, is a good succulent for colder gardens. They grow well in hot, dry, rocky areas of the garden and overwinter well even if temperatures drop significantly. Orange sedum (Sedum kamtschaticum), whose leaves change to orange in the fall, and golden carpet (Sedum acre) are winter hardy to USDA zone 4.