Many cactus plants have a sculptural quality to them. Those species that also flower are especially striking. Cactus flowers tend to be oversized with petals featuring a shimmery quality. Bloom colors range from dazzling white to everything but true blue and black. You'll often see several colors in the same flower. Most cactus bloom in the spring, opening during the day. Some species flower at night and are pollinated by bats or moths. Cactus flowers tend to last just one day.
After resting all winter and experiencing spring rain, many cactus bloom in the spring months. At that time, temperatures aren't yet excessively hot, so the plants are primed to put on an extravagant floral display. Even if rains are sparse, cactus draw upon their stored water to flower, but not as abundantly.
In Arizona's Sonoran Desert, cactus begin to bloom in March, with April being the month of the most flowering. In May, prickly pears (Opuntia spp.) flower. This species is hardy in U.S. Department of Agriculture (USDA) plant hardiness zones 3b through 11.
Cactus that flower in summer's heat are generally substantial specimens that have stored a significant amount of water. The stored moisture helps them bloom reliably when daytime temperatures climb.
Saguaros, hardy in USDA zones 9a to 10b, are well known for their striking blooms that open at night for visits by bats. These impressive plants, which reach 40 to 60 feet tall, don't begin flowering until they're 40 to 50 years old. The saguaro (Carnegiea gigantea), which reaches 30 to 50 feet tall, flowers in mid-May to mid-June when temperatures in its native Sonoran Desert regularly surpass 100 degrees Fahrenheit. The plant features many waxy-petaled flowers that encircle branch ends.
Heavy-bodied barrel cacti (Ferocactus spp.) is another cactus variety that blooms from spring into summer with yellow, orange or bright red flowers, depending on the species. Fishhook barrel cactus (Ferocactus wislizeni) grows to 5 feet tall in USDA zones 8 through 11. It produces yellow blooms.
Some cactus flower at night, which enables the plants to conserve water during the warm months. Peruvian apple cactus (Cereus repandus) typifies a moth-pollinated flower. The trumpet-shaped bloom is 5-inches in diameter and features a sweet fragrance. The apple cactus blooms most abundantly in spring, with a fall rebloom possible. The plant is blue-green in color and grows in a 20-foot-tall column, branching at the base. This cactus needs frost protection in USDA zone 9 and is hardy in zones 10 and 11.
Night blooming cereus (Hylocereus undatus) displays another large moth-pollinated white flower. It blooms in spring and summer on flattened stems that resemble long, scalloped leaves. This cactus is cultivated for its oval, red fruits, known as dragonfruit. This plant is hardy in USDA zones 10 and 11.
The familiar Christmas cactus announces its season of bloom through its common name. With its flattened, leaf-like stem, Christmas cactus (Schlumbergera truncata) grows as an epiphyte in tropical forests of southeastern Brazil. Many hybrids and cultivars now exist, with red, white, pink, purple, peach and salmon-colored blooms that usually occur in winter.
When grown as a houseplant, in order to bloom at Christmastime, Christmas cactus requires cool nights and more than 13 hours of darkness during each 24-hour period. Hardy to USDA zones 10 through 12, Christmas cactus flowers best when it's slightly pot-bound. It's also called Thanksgiving cactus, because it can be manipulated to bloom in November.