Blue Myrtle Cactus
Myrtillocactus geometrizans or as it is also commonly known Blue Myrtle Cactus is a distinctive-looking shrub cactus that is easy to grow and makes a great houseplant.
The beauty of Myrtillocactus geometrizans is its evolving form. It initially grows as a singular column-shaped cactus that grows skywards but as it matures, it develops multiple candelabra-esque branches to create its shrub-like appearance.
Position Full sun once matured
Watering Water thoroughly but infrequently
Size Up to 16 Ft (5m) tall (stem diameter: up to 4 inches (10cm))
Climate Semi hardy Zones 9a to 11b (25° F / -4° C)
Propagate Stem cuttings, seeds
Seasonality Evergreen, Winter Dormant
Toxicity Mildly toxic to animals
Flowers Greenish-white blooms from February until April
This architectural cactus is instantly recognizable by the ribbed verticals, that exhibit characteristic small spikes that grow from evenly spaced areoles.
Although predominantly green, this cactus boasts beautiful tonal hues of grey and blue that add interest and character and make this cactus a real talking point. Unsurprisingly, it has acquired a number of other names due to its blue-green-grey color and also its fruit production. Other than Myrtillocactus geometrizans and Blue Myrtle cactus, it is also known as; Blue candle; Whortleberry cactus, and Bilberry cactus
Native to northern and central Mexico, Myrtillocactus geometrizans are easier to care for than you might think. In fact, they are a great houseplant for cactus-growing enthusiasts or even those new to cacti.
You can expect to see small greenish-white blooms from Spring. Sadly these sweet-smelling flowers only last for one day but are attractive to bees and other pollinators. However, shortly afterward, oblong-shaped dark blueish-purple berries appear are sweet-tasting, edible, and considered a snack in Mexico.
Unless you live in a super-hot climate, this plant is best grown indoors. In the summer months, a matured plant needs plenty of direct sunlight but for younger plants, position it in a sunny spot with partial shade to avoid scorching its tender stems.
During the winter months, this cactus should be moved to a slightly cooler position but still in a bright spot with plenty of natural sunlight. Moving it to a cooler position will help to encourage flowering in the following year.
This cactus is only semi-cold hardy and will only tolerate temperatures as low as 22° F / -4° C for very short periods.
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Height and Spread
A well-cared-for plant of this species is relatively fast-growing as Cacti go and can grow up to 5m tall and each stem (or branch) is able to grow up to 10cm in diameter. Initially, Myrtillocactus geometrizans will grow just one solitary column, and the ‘candelabra’ branches that form the cactus shrub will begin to develop as the cactus matures.
As is the case with most other Cactus, Myrtillocactus geometrizans do not require much watering. During the summer months, water thoroughly and at regular intervals but infrequently. Always allow the soil around your cactus to dry completely between watering.
In the winter, watering should be kept to an absolute minimum. Myrtillocactus geometrizans has a summer growing season and essentially lays dormant during the winter months. Whilst your plant will still grow during dormancy, it does so at a much slower rate and so has less requirement for water and nutrients.
As with summer watering, only water when the soil around your cactus is completely dry.
You can test the dryness of the soil by pressing your finger at least a quarter of an inch into the soil or prodding the soil around the drainage holes in the bottom of the pot. If the soil feels dry, you can go ahead and water your cactus with a small spout watering can.
It’s useful to know the signs to look out for that could indicate if your cactus has been overwatered. Indicators of over-watering include soggy, mushy, and brown-colored stems. You may also start to notice a reduction in growth.
If the stems or branches of your Blue Myrtle cactus look wrinkly and feel soft, then it’s likely that it needs water. You may also notice the spines feeling dry or brittle and if touched, may easily fall off.
One further word of caution about watering your Myrtillocactus geometrizans. Don’t be tempted to use a spray bottle or mister as a watering device. This plant will not fare well with high levels of humidity and any long periods with damp stems or branches may cause them to wilt.
Always use well-draining soil when planting Myrtillocactus Geometrizans. The roots need to be free from excess moisture to receive the oxygen they need to thrive.
Use peat-free soil or coconut coir mixed with minerals such as grit, sand, or perlite. Planting in the right type of soil will encourage healthy growth and help to prevent root rot and disease.
You can make your own well-draining soil easily at home. Mix together two-thirds of minerals such as grit, sand, or perlite, with one-third of organic matter, such as a good quality peat-free compost or coconut coir.
Ready-mixed cactus soil is also readily available to purchase online or at any decent garden-supply retailer.
Since Myrtillocactus geometrizans is relatively easy to grow, the only special requirement it needs is a well-rested winter period. This will give it the best possible chance of flowering successfully the following year.
You can provide a well-rested winter period easily by reducing the frequency and amount of water and also moving it to a cooler position during the winter months.
Then the following spring you can expect to see small greenish-white blooms.
The flowers are fleeting and do only last for one day however, they are quickly followed by oblong-shaped blueish-purple berries, that are sweet tasting and edible.
To encourage a good, strong root system and healthy growth use a balanced cactus fertilizer every 4 weeks during spring and summer. There’s no need to fertilize your Myrtillocactus geometrizans in winter.
It’s unlikely your Blue Myrtle cactus shrub will need pruning. The continually developing and growing candelabra-style branches are the feature of this plant.
Blue Myrtle is a fast-growing dense shrub cactus so expect to need to re-pot at least every other year. They require a reasonable amount of space in which to grow but don’t like excess soil as this can affect the growth and development of a healthy root system. Just monitor your plant’s growth a report it into a suitable succulent pot every couple of years.
How To Propagate Blue Myrtle
Blue Myrtle can be propagated from seed or stem cuttings. This should take place during the summer and only after flowering.
After flowering, collect seeds from ripe fruits. Before sowing the seeds directly into well-draining soil, clean and dry them thoroughly. Ensure that all frost has passed before sowing.
Water very gently to begin with then wait until the soil is completely dry before watering again. Continue with watering thoroughly and regularly. Avoid placing the seedlings in direct sunlight. Young plants and seedlings need a warm, well-ventilated, and sheltered position with plenty of light and partial shade if very hot.
To propagate from cuttings from a branched plant, use a sterile and sharp knife to remove a stem. Cut as close to the stem junction as possible. Place the cutting on a tray lined with kitchen paper and allow the cut surface to dry out (callous) for 2 to 3 weeks.
Once completely dry, plant the cutting in well-draining soil. Water once and then wait until the soil is completely dry before watering thoroughly and regularly thereafter.
Avoid placing your cutting in direct sunlight. Young plants and seedlings need a warm, well-ventilated, and sheltered position with plenty of light and partial shade if very hot.
Common problems with Blue Myrtle
Over-watering, allowing the soil to remain wet, or not using well-draining soil are all common causes that can lead to root rot in a Myrtillocactus geometrizans cactus.
Identifying root rot is not always simple but there are a number of tell-tale signs to look out for. These include the top of the cactus becoming saggy or turning yellow, an unpleasant smell, or the main stem turning brown at the base just below the soil level.
To treat your Blue Myrtle for root rot you should first remove it from its pot. Then, very carefully brush off any soil that remains around the roots.
Roots that are brown or black and soft and mushy are rotten and need trimming off. Always use sharp, sterile scissors or a knife to remove root rot, and allow the cut to dry before repotting with fresh soil in a clean pot.
Water thoroughly, but less frequently thereafter.
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