Cacti are flowering plants, so every kind of cactus is capable of blooming when it is mature. Whether or not an individual cactus plant blooms depends on its age and the care it gets. Some cacti don’t bloom until they are more than 30 years old. Others won’t bloom, even if they are old enough, unless they get proper light conditions, watering and fertilization. This is especially true for potted cacti. Holiday Cacti grown indoors, such as Christmas Cactus, won’t bloom unless they get long nights and short days.
Columnar Cacti
Tall-growing columnar cacti often take years before they bloom for the first time if grown from seed. If you root a branch from a mature, already-blooming columnar cactus, it will keep blooming after it is separated from the mother plant and rooted.
However, some cacti, such as Saguaro (Carnegiea gigantea), native to Arizona in U.S. Department of Agriculture plant hardiness zones 9 through 11, have branches that won’t root, so Saguaro has to be grown from seed, with a 40- to 55-year wait for the first flower.
Some columnar cacti that produce flowers for the first time after 10 to 20 years and can live outdoors in USDA zones 9 through 11 are Peruvian Apple (Cereus repandus) with blue stems and large white night-blooming flowers, Senita Cactus (Pachycereus schottii) with gray-green stems and small pink flowers produced amid an area of dense shaggy spines, and Mexican Fence Post (Pachycereus marginatus) with bright green stems that have white-defined stem ridges and smaller white flowers. Columnar cacti are effective landscaping plants even without flowers.
Short-stem Cacti
Short-columnar cacti with mature stems below 2 feet (60 cm) tall usually flower within five years from germination. Hedgehog Cacti (Echinocereus spp.) are native to the United States and Mexico, and make mounding clumps of many stems over time. Large pink, magenta or red flowers are abundant in spring.
Depending on the species, Hedgehog Cactus grows in USDA zones 5, for red-flowered short claret cup (Echinocereus coccineus), through 11. Easter Lily Cactus (Echinopsis oxygona and hybrids) are hardy in USDA zones 8 through 11. They produce huge funnel-shaped flowers in white, pink, lavender, magenta or red.
For the size of the plant, Peanut Cactus (Echinopsis chamaecereus) produces large flowers. Stems up to 6 inches (15 cm) long, covered with weak white spines, crawl along the ground and produce abundant bright orange flowers over 1 inch (2.5 cm) wide in spring. Peanut Cactus grows outdoors in USDA zones 8 through 11.
Round Cacti
Some of the most floriferous cacti belong here, such as Pincushion Cacti (Mammillaria spp. and hybrids) and Rebutias (Rebutia spp. and hybrids). They usually bloom within three to four years after sprouting.
Pincushion Cacti are native to the United States and Mexico, producing star-shaped flowers in a ring around the top of the stem. Although round when young, some elongate to small columns.
Flowers are white, pink, magenta, lavender, red, yellow or green, and plants grow outdoors in USDA zones 8 through 10. Rebutias are native to South America. Tidy low-growing plants cluster with age, and red, yellow, orange or purple flowers come from near the base of the stem. Rebutias are hardy in USDA zones 9 through 11.
Conditions that Encourage Bloom
Since cacti grow as container plants in any USDA zone, give them proper care and they will reward you with blossoms. Most cacti need at least four hours of sunlight a day, preferably morning sunlight. Water them regularly during the growing season, allowing the top inch or two of soil to dry before watering again until water comes through the pot’s drainage holes.
Don’t let water remain in pot saucers. Use well-draining soilless potting mix. Fertilize them monthly from when they begin spring growth to the end of summer with a half-strength low-nitrogen high-phosphorus formula, which promotes bloom. Allow the cactus to become somewhat pot-bound for best bloom. Decrease watering in winter, and give your cacti a winter dormancy period with lower temperatures (50°F/10°C).
Holiday Cacti
Thanksgiving Cactus (Schlumbergera truncata) and Christmas Cactus (Schlumbergera bridgesii) look so different than desert cacti that some people are surprised that they are cacti.
They look different because they grow on Brazilian rain forest trees as epiphytes, and their stems are flattened and green, looking leaf-like. They need different care than desert cacti. Holiday Cacti are triggered to bloom in fall and winter by cooling temperatures, increasing night length and decreasing day length with only 8 to 10 hours of light. Most of the year they prefer partial shade, but in fall and winter they can be in sunlight.
Source: sfgate.com
