About ten species of evergreen climbing plants belong to the allamanda genus, originating in Central and South America. In nature they grow up to 10-12 meters in length, while the specimens grown in pots remain within 100-150 cm in height, and are often grown in hanging baskets. The stems are thin, but quite leathery, they bear numerous large glossy, thick, slightly leathery leaves, of a brilliant dark green, oval color; from late spring to the first colds at the apex of the stems they produce numerous large flowers gathered in racemes; the flowers of allamanda cathartica are trumpet-shaped, and have large dimensions, up to 8-10 cm in diameter from the corolla; they are golden yellow, while the flowers of A. blanchetii, another widely cultivated species, are pink or purple. The flowers are followed by roundish berries, covered with a thick down, which contain numerous winged seeds.
The plants of allamanda cathartica do not tolerate temperatures below 3-4 ° C for prolonged periods, so they are generally grown as houseplants; in regions with very mild winters they can be used as garden shrubs, placing them in a sheltered place from the wind and cold. To obtain an abundant flowering it is necessary that these plants are placed in a very bright place, that is struck directly by the sun's rays for at least 3-4 hours a day, but not during the hottest hours, therefore better the morning or late sun afternoon.
During the cold months the allamanda cathartica it is watered with moderation, avoiding to soak the soil too much; from March to October water regularly and abundantly, avoiding in any case the water stagnation that is very harmful for this type of plant, but checking that the soil maintains the right degree of humidity. Provide fertilizer for flowering plants every 15-20 days. In autumn, after flowering, too long branches are pruned to obtain a more compact shrub.
To have a good development of the specimens of this type, it is advisable to cultivate in a good soil rich in organic matter, slightly acid, very well drained; to increase drainage it is advisable to add to the earth of our pots a good part of pumice stone or lapillus.
This plant is repotted annually in the early spring period until a 50 cm pot is used; at this point, every year it is good to intervene eliminating the superficial layer of the soil and replacing it with a compound rich in organic matter.
The multiplication of the allamanda cathartica occurs by seed, in late winter, or by cuttings, in autumn or spring. The cuttings should be placed in containers in which a mixture of peat and sand has been placed; these must then be placed in a sheltered and protected place where the temperature remains constantly around 22 ° C.
Allamanda cathartica: Pests and diseases
These climbing plants can be attacked by the cochineal and the red spider mite. The attack of the cochineal is very recognizable, due to the presence of formations that look like cotton flakes; if the presence is contained, it is possible to intervene by manual elimination with a cloth soaked in alcohol or by washing the plant with soap and water, which is then rinsed with great care. Otherwise, if the presence of scale insects is massive, it is good to use a specific product to be sprayed on the plant. To eliminate the red spider it may be sufficient to increase the environmental humidity and vaporize water on the leaves.