The plants of the genus nepenthes are all carnivorous plants, originating from the tropical belt, which extends from Asia to the Philippines, almost to Australia, and some species also present in Madagascar; some species develop in areas near the sea, or characterized by constantly mild temperatures, throughout the year; other species are characteristic instead of mountain areas, and can enjoy some cool hours every day, with days characterized by periods with strong temperature changes; few species then originate from areas actually located at high altitudes, and therefore can withstand brief frosts. In the nursery are generally found hybrids, derived from species gathered in the group of nepenthes lowland, or low altitude, le nepenthes plain, used to living in areas with tropical, warm and humid climate.
These plants develop as long lianas, which dangle among the trees, and therefore have thin stems, with thick and slightly cuoiose leaves, characterized by tendrils, which allow them to stick between the leaves and the stems of the other trees; the traps are made up of leaves transformed into a sort of enlarged bottles or flasks, of the type of skins, covered by an upper lip, which often prevents the rain water from entering the trap itself. The color of the traps is green, with various reddish or brown spots; they are large and filled up to almost half of a more or less viscous flow depending on the species; the upper part of the traps is covered by scales that make it slippery, so that trapped prey finds it difficult to escape. The fluid inside the traps is formulated in such a way as to trap the preys and drown them; it also contains enzymes that will digest the prey, and special glands placed at the bottom of the trap will assimilate the mineral salts.
In nature there are nepenthes of various sizes, with lianas up to 8-10 meters long and large leaves, with traps that can contain up to two liters of fluid; in the nursery we find species and hybrids of decidedly smaller dimensions, with traps generally of a size close to 10 cm.
The nepenthes in nature also produce panicle inflorescences, consisting of cream or white flowers, with a particular musk aroma; the plants are dioecious, therefore a plant produces only male or female flowers, and therefore if we have only one plant its flowers surely will not give birth to fertile seeds.
Despite being plants of tropical origin, the conditions of cultivation of the nepenthes is quite similar to that in which we grow most of the carnivorous plants present in the wild state in Italy, apart from the temperatures; it is in fact plants that fear the cold, and that must be grown in a warm climate, with minimum temperatures never lower than 12-15 ° C. The nepenthes are therefore apartment carnivorous plants, which can be moved outdoors only in very hot seasons, starting from May-June, until August-September; they prefer very sunny positions, or in any case where they can have at least a few hours a day of direct sun, even if in summer it is good to choose a semi-shaded exposure, especially in the hottest hours of the year. If it is true that the average annual temperatures in the tropical areas of the globe are much higher than the Italian ones, it is also true that in these areas there are no periods of the year with large temperature ranges, therefore life in the apartment, with about 20-22 ° C of average, is the best, as far as temperatures are concerned. These plants are rarely cultivated in terrariums, because even the smallest species, with time tends to become bulky, and therefore would need a decidedly too large terrarium.
Apart from these particular needs with regard to temperatures, in reality these plants do not need a very different climate compared to the one where a sundew is grown, much warmer in winter, yes, but otherwise the environmental humidity and watering they will be practically the same: very high air humidity, and very regular watering, so as to keep the soil almost always moist.
As always, remember that damp is not synonymous with soaked, saturated with water or stagnant; it simply means that the watering will have to be regular, wetting the ground every time it tends to dry, and avoiding to leave water still for days in the saucer. When we water, we try to wet the ground and not the leaves or traps, we use demineralized water, or rain water, to avoid overloading the soil with the limestone contained in the tap water of the house. In addition to watering, it is also essential to keep the air very humid; unfortunately at home during the winter, and in the garden in summer, the air in Italy tends to be decidedly dry, so we will be forced to vaporize our nepenthes frequently, to raise the humidity around the plant a lot.
A nepenthes in dry air tends to dry out the traps, and then to conspicuously waste away.
Soil and fertilization
The nepenthes in nature develop as epiphytic plants, or their reduced root system sinks into the decomposed leaves that can be found in the undergrowth, or even at the intersection of the branches of large trees, as happens for many orchids of tropical origin; just like we do for a phalaenopsis, even our nepente will be cultivated in a fairly small container, filled with peat, small pieces of bark, little pumice stone: a very soft, permeable soil that slightly retains moisture. In general they do not repot often, but when it is done it is used peat and bark, avoiding the ready soil, like universal soil, because they are often fertilized.
In fact, as with most carnivorous plants, even the nepenthes do not like a high presence of mineral salts in the soil, which can irreparably ruin even a large and adult plant.
In fact, these plants obtain the nitrogen and mineral salts they need by digesting the prey they catch.
Nepentes: A particular plant and its infauna
The nepenthes are carnivorous plants slightly different from the others, mainly because they develop large traps; some species, in particular areas of the globe, have developed a particular symbiotic relationship with some insects, which instead of being caught and digested by traps, live in them and feed on part of the prey captured by the plant.
Generally in some species of nepenthes it is easy to find a microcosm inhabited by mosquito larvae, which splash around in the fluid contained in the traps, without it hurting them; it is still not clear how this happens, and when this can benefit plants.