Carnivorous plants: Drosera
The genus Drosera has about one hundred and fifty species of carnivorous plants, spread practically all over the globe; most of the species however originate from Australia and southern Africa; as is the case with all carnivores, these are plants that live in marshy or peat bogs in nature, characterized by high humidity in the soil and air, and by a low quantity of mineral salts dissolved in the soil. The most widespread species in cultivation, and which is most easily found in the nursery, is Drosera capensis, native, as the name suggests, of southern Africa.
All the species form a dense rosette of leaves, which have a linear or spatula shape, more or less enlarged, and a light green or reddish color. The whole surface of the leaves is covered with a thin red hair: at the apex of each small hair (which works like a tentacle) a small droplet of a transparent adhesive substance is clearly visible, which is used to trap prey. When to a leaf of sundew an insect rests, it remains stuck to the glue present on the leaf, which rolls up, in order to bring the prey towards the base of the leaves, where there are pelts equipped with droplets of a digestive enzyme; after having "eaten" the insect, the leaf unrolls, returning to its original position. It can happen that the sundews catch larger preys than usual, in this case, the leaf that has trapped them, usually dries up after the insect has been digested.
In spring, a thin stem rises among the leaves, which bears large, highly decorative five-petal flowers.
There are several varieties of sundew, many of which are used to living in a shady environment, away from direct sunlight; drosera capensis, and some other species prefer the well sunny and very bright positions; in purchasing a sundew we immediately inquire about the species, in order to know the lighting needs, fundamental for the development and health of the plant.
As is the case for most carnivorous plants, sundews are also used to living in peat bogs and marshes, with a soil very low in mineral salts, and a very high constant humidity; to cultivate the sundews it is therefore placed in a soil made up exclusively of peat, mixed with a little sand or perlite, to prevent water from allowing the roots to breathe.
In any case, we avoid the use of ready-made soil, such as universal soil, these soil in fact contain a good amount of nitrogen, which is fatal for carnivorous plants, even if in low concentrations. In fact, these plants get the nitrogen they need from the prey they capture, and are used to living in areas completely free of mineral salts dissolved in the soil; contrary to what happens for other plants, therefore, for carnivorous plants, fertilization can be a fatal operation, which leads to the complete drying of the entire leaf system.
The sundews that are commonly found in the nursery are not cold-resistant, therefore these plants are grown in a cold greenhouse, or in any case in a cold place, where, however, the temperatures never drop below 5 ° C, under penalty of loss of foliage , and sometimes even the whole plant.
Instead, they need constant humidity, and generally are placed in low trays, or in bowls, filled with peat and sand, placed in large and capacious saucers, in which about 2-3 cm of water are constantly kept, for throughout the year, so as to imitate as much as possible a humid environment. Let's avoid growing carnivores in pots, unless we have a closed terrarium, where it is possible to control humidity and temperature.
The watering must be provided often and regularly, preventing in any way the soil from drying out completely; to avoid weighing down the soil with mineral salts, thus undermining the health of the plant, it is advisable to water the sundews using demineralized water.