The Callistemons are widespread plants in gardens, even if their origin is quite exotic; in fact, these plants come from distant Australia, from areas where the climate is not so different from the Mediterranean. They belong to the family of blueberries, like the common myrtle, in fact the callistemon flowers are very reminiscent of those of the myrtle: they are made up of small petals, which pass almost completely unobserved, the most noticeable part of the flower are the long stamens, gathered in an elongated bunch. In particular the flowers of the Bottlebrush they are also gathered in long spikes, which give the plant a bizarre appearance, given that the inflorescences are reminiscent of long fire-red pipe cleaners.
The Bottlebrush produces long, linear, dark green leaves with a papyrus consistency; from late spring to summer it produces innumerable inflorescences, typically of a fiery red color, although there are callistemon with yellow, orange, white and pink flowers.
About 30 species belong to the genus, all evergreens, some are large shrubs, other real trees; in Italy, in nurseries, we generally find only the species Callistemon citrinus, and the species callistemon viminalis, with arched or pendulous branches.
How to grow it
The exotic origin of Callistemon must not frighten us, in reality success in Italian gardens is due to the ease of cultivation; they prefer very sunny positions, and they fear the shadow, which prevents the flowering and also the harmonious development of the plant; they do not need particular soil, as long as this is not heavy or free of drainage, any fairly rich universal soil may be fine.
They can withstand some short periods of summer drought, but from April to September it is advisable to water the plant, always waiting for the soil to be dry between one watering and another; this may mean that one watering a week in spring is enough, but that in summer we will have to water the plant almost every day. We avoid to drown the roots with abundant waterings: let's wet the soil and wait for it to dry before watering; if the plant stays dry for a day or two at most we will see it collapse, but it will recover as soon as we water it. In the vegetative period we mix the water of the watering, every 10-12 days, with a specific fertilizer for flowering plants, which will favor the production of new buds.
At the arrival of autumn we thin out the waterings, and we try to difar so that with the cold the plant remains in a ground that is always very dry; if we live in an area with very rainy winters we cover the soil around the plant, to avoid it receiving watering without our knowledge.
The climate of the callistemon
These plants come from areas with fairly mild winters, where frosts occur very rarely, and the average temperature remains above 4-5 ° C for most of the winter; this makes the Callistemone quite little suitable for the gardens of northern Italy, instead they develop perfectly in the central south, where they are fully cultivated as garden plants. For those who live in the north there is nothing left to do but to cultivate the Callistemon in pots, so that it can be moved in the event of frost or intense and prolonged cold.
In fact, the cultivation of these shrubs in Europe has been going on for many years, during which they have also obtained varieties that are more resistant to the cold than their Australian cousins; when we buy our Callistemone we ask the nurseryman if it belongs to a cold resistant variety; in any case, in winter, let's cover it with non-woven fabric, so as to avoid it being completely exposed to the elements.
Callistemone - Callistemon: Special treatments
If cultivated in a particularly dry climate, callistemons tend to be attacked by the cochineal, which must be promptly eradicated, using white oil, far from flowering, to avoid disturbing useful insects.
At the end of winter, therefore, we generally proceed with a treatment based on white oil, which avoids the recurrence of the problem; in the same period of the year we will practice a light pruning: since the plant tends to develop slowly, it generally does not need pruning, but in February-March it is good to remove the foliage ruined by the cold and the broken or poorly developed branches.
During the pruning we can also collect the small seeds, to try to make them germinate, in a mixture of peat and sand in equal parts, to keep moist until germination of the seeds.
To propagate our callistemone, above all it is a hybrid, we can also practice cuttings, taking them from those branches that have not bloomed, in spring or late summer; the young cuttings should be kept in a damp soil, in a cool and sheltered place. Recall that callistemons develop very slowly, so starting from a small cutting we will take a few years to have a good sized shrub.
These plants do not like excessively calcareous soils, if cultivated in a very calcareous area, or watered with water rich in limestone, they can be affected by ferric chlorosis: all the foliage tends to become very light in color and the plant perishes; in these cases the use of a soaking fertilizer generally improves the condition of the plant rapidly.