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Classification, origin and description
Common name: Hibiscus.
Etymology: derives from the Greek name, ebisckos and ibiskus, already used by Dioscorides to indicate a species of mallow.
provenance: Southern United States, South America, Africa, China, Japan, India, Syria, Italy and Mediterranean regions.
Genre description: includes about 250-300 species of shrubs, small trees or herbaceous plants, perennial or annual, rustic or delicate, evergreen or deciduous. In all species the flowers, which usually appear at the axil of the leaves (but also at the apex of the branches), are funnel-shaped, simple, semi-double, double or strado and, in any case, very showy. The calyx is formed by five sepals, arranged to wrap around the base of the flower. The corolla is made up of five identical petals (in simple flowers), flared at the ends or planes, well spaced from each other or slightly superimposed on each other. The stem column emerges from the center of the flower, on which the stamens are arranged and which may be longer or shorter than the corolla, but which in any case carries the stylus, ending with five pistils, on its extension. The flowers are odorless, with the exception of those of the species H. arnottianus and H. waimae, with a slight perfume. The varieties and hybrids on the market today have been obtained from a few horticultural species and can be divided into two large groups: tropical hibiscus (derived from H. rosa-sinensis) and rustic hibiscus (derived from H. syriacus or Rosa di Sharon) .
Hibiscus rosa-sinensis (photo website)
Hibiscus flowers (website photo)
Species and varieties
Hibiscus arnottianus: native to the Hawaiian islands, it has white or pinkish-white flowers. It has wrinkled light green (almost olive) semi-deciduous leaves: they fall at the end of winter and reappear immediately afterwards at the beginning of spring. It can be easily pruned (so much so that it is also used as a hedge plant). Even drastic cuts, which could adversely affect the flower production of H. rosa-sinensis, do not reduce the flowering capacity of this species.
Hibiscus brackenridgei: species native to the Hawaiian islands that has flowers with yellow or reddish corollas, which have become the symbol of the islands.
Hibiscus coccineus: comes from the south of the United States this perennial herbaceous species has stems and petioles with reddish hues, the same as those taken from palmate leaves, at the juvenile stage. The red, solitary flowers, up to 15 cm wide, which appear in the summer, are followed by large capsules, wrapped in five very decorative bracts. It is a semi-rustic species that grows up to 2.5-3 m.
Hibiscus manihot: this perennial herbaceous species, which is usually cultivated as an annual, has dark green colored palmate-leaves, at the axilla of which, in summer, 15 cm wide flowers appear, yellow, with a purple center. It is a rustic plant, which can be grown outdoors.
Hibiscus militaris: it has palmate leaves with three lobes (the central one is larger than the others) and pink-red flowers (which bloom in July-August) this herbaceous, rustic and perennial species native to South America.
Hibiscus moscheutos o H. palustris: semi-rustic and perennial, this herbaceous species, native to the southern countries of the United States, has 15 cm wide flowers. pink, which bloom in summer. It grows up to 1.5 m. and there are varieties with white and dark red flowers.
Hibiscus mutabilis: this semi-rustic and perennial shrub species, originating from China, has heart-shaped and tomentose leaves. The flowers (10 cm wide), which appear at the axil of the highest leaves, are carried by thin petioles (5 cm long) and during the single day of life they take on a color that varies from the white of the morning, to the opening, pink and dark red, in the evening, before wilting. It can grow up to 1.8 m. in height.
Hibiscus pentacarpos: perennial and rustic, this species, originally from Italy, has lobed leaves and small, mauve-colored flowers that appear in the summer. It grows up to 30-40 cm.
Hibiscus rosa-sinensis: native to China, this shrubby, perennial and semi-rustic species is the best known and most commercialized. It has glossy, dark green leaves, with an irregularly toothed margin and a sharp apex. The funnel-shaped flowers are solitary and appear on the branches of the year, in the axil of the upper leaves. From the center of the corolla, formed by five intense crimson expanded petals, the stem column emerges, which has, on the upper part, the stamens and, at the apex, five pistils. They bloom profusely from June to September and this compensates for their poor individual duration. In the country of origin it assumes an arborescent aspect, growing up to 8-10 m., While in our pot, it can reach 3-4 m. in height. Numerous varieties and hybrids with double or semi-double flowers have been created, varying in color from white, pink, yellow to orange. Among the best known varieties we find the "Cooperi", with very decorative leaves with white and crimson spots and with carmine margins and striated foil of the same color; the scarlet flowers are smaller and less abundant than those of the type species.
Hibiscus roseus: herbaceous, perennial and rustic, this species, typical of the Mediterranean regions, bears well the salty winds. In July-August it produces 10 cm wide flowers. pink color. It grows up to 0.5-1 m.
Hibiscus schizopetalus: this species with a shrubby bearing, not very resistant to the cold and with branches so fragile, that requires the support of a guardian, in order to avoid breaking it, is native to East Africa. The leaves are small and the flowers, pendulous (which earned him the name of "Japanese Lantern") and about 8 cm wide, varying in color from dark pink to orange-red, have the petals fringed and curved backwards which leave in evidence the long red stamens. It grows up to 3 m. height and 2.5 m. wide.
Hibiscus syriacus o Althaea frutex: coming from Syria, this rustic, highly branched shrub has deciduous leaves, oval in shape and dark green in color, with the toothed margin and sometimes three-lobed. From July to October it produces 8 cm wide flowers. which appear in the axilla of the upper leaves, assuming shades ranging from white to purple. As with H. arnottianus, even drastic cuts, which could adversely affect the flower production of H. rosa-sinensis, do not reduce the flowering capacity of this species. On the market there are many varieties among which we remember: "Ardens", double pink flowers with purple spots; "Blue Bird or Oiseau Bleu", with gentian blue flowers; "Caeleste", with blue flowers; "Dorothy Crane", with white flowers with a crimson center; "Jeanne d'Arc", with double white flowers.
Hibiscus trionum: native to Africa and Italy, this annual and rustic herbaceous species has dark green oval leaves with toothed margins. The flowers, 8 cm wide, which appear from August to September in the axil of the leaves, are pale yellow in color with a brown center and have a swollen calyx of seeds and very showy. They only hatch for a couple of hours in the morning, although now there are varieties of flowers that remain open until the evening. It grows up to 50-80 cm.
Hibiscus syriacus - Hibiscus of Syria (photo website)
Environmental requirements, substrate, fertilizations and special precautions
Temperature: the delicate shrubby species need a winter temperature of not less than 5-10 ° C (they must therefore be grown in a greenhouse or apartment). If the temperature does not drop below 16 ° C and the soil is kept humid, Hibiscus, especially those with variegated leaves, can behave like evergreens.
Light: very good. They also tolerate full sun, provided that the humidity increases; in the inability to do so, better shade.
Watering and environmental humidity: watering must be abundant in summer (almost daily) and reduced in winter; the ambient humidity must be kept high, but not stagnant (Hibiscus need air). For watering it is preferable to choose early in the morning or in the evening after sunset, avoiding the hottest hours, in order to prevent thermal shocks due to the difference in temperature between the soil and water.
Substrate: mixture of potting soil, soil of mature leaves and peat, with the addition of sand to increase drainage.
Special fertilizations and tricks: administer liquid fertilizer in the summer months. They repot every year in March. Plants, which can be kept outdoors in summer, need protection for the winter months. The ideal environment should be bright and with a temperature of not less than 15-18 ° C, to avoid the fall of the leaves, which will instead occur at lower temperatures, which in any case must not be less than 5-10 ° C. During the winter, the only attention must be to keep the soil moist. In May (and not before) they can be taken outside again. The change of environment can cause yellowing and fall of part of the leaves; but in a few weeks the vegetation will be renewed. The withered corollas fall on their own (they can be easily removed with a tap of the fingers).
Multiplication and pruning
Multiplication: the annual species reproduce by sowing them, in April, directly at home and thinning them later at the desired distance. Perennial species multiply, in July, placing cuttings obtained in a mixture of peat and sand, taking lateral shoots of 8-10 cm in length. The ideal temperature is between 18 and 21 ° C. and it is preferred to avoid covering the cuttings, in order to avoid rotting which would certainly cause death. After rooting, the seedlings will be transferred to progressively larger pots.
Pruning: until the plant has reached the third-fourth year of age it is better to avoid pruning. Subsequently the specimens grown in pots are pruned annually in March. For the H. rosa-sinensis species, which blooms on the branches of the year, the training prunings must be carried out before the new branches appear, in order not to reduce their flowering capacity. Instead, frequent topping can be carried out to increase the development of collateral ramifications.
Diseases, pests and adversities
- Aphids: they can attack young branches, buds and flowers in particular. They stimulate the plant to produce sugary substances that make it easily subject to the attack of fumaggini. They fight with specific insecticides.
- Cotton mealy bugs: can attack plants, especially in hot and dry climates. You have to remove them, treat the plant with an anticoccidic product and raise the humidity level (the spraying and the washing of the leaves allow to eliminate the cochineals in the larval state). As an alternative to the chemical, the affected parts can be rubbed with a cotton swab wet with water and alcohol.
- Brown mealybugs: they occur with the formation of brown growths (determined by the small "shell") and giving the plant a blackish and sticky appearance (due to the production by the plant of sugary substances that make it subject to attack by fungi and fumaggini). They are fought by removing them and treating the plant with an anticoccidic product or by rubbing the affected parts with a pad soaked in water and alcohol.
- Powdery mildew or white malt: it is caused by mushrooms of the Eirisifacee family. It is the cause of the appearance of powdery white spots on leaves and stems, characterized by a typical musty smell. Treat the plant with a fungicide.