The Blue Myrtle Cactus (Myrtillocactus geometrizans) is a popular columnar cactus cherished for its striking blue-gray stems and candelabra-like growth habit. Originating from the arid regions of Central and Northern Mexico, this species is relatively fast-growing. Many enthusiasts cultivate this plant hoping to witness its unique blooming cycle, which leads to the production of an edible fruit. Transitioning this desert plant from its vegetative phase to its reproductive flowering stage requires specific manipulation of its environment.
Essential Conditions for a Healthy Cactus
Cultivating a healthy specimen capable of flowering begins with replicating the intense environmental conditions of its native habitat during the active growing season. The Myrtillocactus geometrizans requires full, bright direct sunlight for strong growth and to maintain its characteristic blue coloration. Insufficient light will lead to thin, pale, and etiolated growth, which will not support flower production.
The potting medium must be exceptionally fast-draining and gritty to prevent root rot. A commercial cactus or succulent mix should be amended with materials like perlite, pumice, or coarse sand to enhance aeration. During the warm spring and summer months, when the plant is actively growing, water deeply and thoroughly. Let the soil completely dry out between waterings, mimicking the infrequent, heavy rains it would receive in the wild.
Fertilization should only occur during active growth (spring through late summer). Apply a diluted, low-nitrogen fertilizer once a month to support energy reserves without promoting weak growth. The cactus must also reach maturity, typically around 24 inches in height, before it is physiologically capable of blooming.
Inducing the Bloom Cycle: Dormancy and Temperature
The most significant factor in encouraging the Myrtillocactus geometrizans to bloom is implementing a winter rest period, or dormancy. In its natural range, the cactus experiences a cooler, drier winter season, which acts as the environmental cue for flower initiation. The plant interprets lower temperatures and reduced moisture as the signal to prepare for spring flowering.
To achieve vernalization, move the cactus to a location where temperatures are consistently cooler, ideally between 40 and 50°F (4–10°C), starting in late fall. While the plant can tolerate brief dips to 25°F, protect it from prolonged freezing temperatures and keep it above 41°F (5°C) to prevent tissue damage. This cool period must be maintained for several months, usually from November through February, to fully induce the bloom cycle.
During dormancy, the watering regimen must be drastically reduced or ceased altogether. The cactus must be kept nearly bone-dry; only provide minimal watering if the stem visibly shrivels, indicating severe dehydration. All fertilizer application must also stop completely during this cold, dry rest. The combination of coolness and drought forces the plant to conserve energy and prepare for spring, when flower buds typically form.
Characteristics of the Flower and Pitaya Fruit
The reward for successfully manipulating the winter cycle is the appearance of flowers, generally emerging in the spring or early summer. These blooms are modest in size, measuring about one inch (2.5 cm) in diameter, and are typically creamy white or pale greenish-white. The flowers have a very brief lifespan, often opening at dusk and lasting for less than one day, a characteristic of nocturnal bloomers.
Following successful pollination, the cactus produces edible fruits known as Garambullo or Mexican Blueberries. The fruit is a globular berry, ranging from dark purple to violet-blue, and measures about 1 to 2 cm across. These berries superficially resemble the bilberry, which is the source of the cactus’s common name. Indoors, where natural pollinators are absent, manual pollination may be necessary to ensure fruit set. The Garambullo fruit is valued in Mexico for its sweet, slightly tart flavor.