Carnivorous plants, carnivores

Carnivorous plants, also known as carnivores, have a special strategy for meeting their needs for nitrogen and other nutrients. Here’s how you need to care for carnivorous plants to keep them growing and thriving.

Origin and way of life

Carnivorous plants (carnivores) are very special plants. Naturalist Charles Darwin was one of the first scientists to deal with this extraordinary group of plants in his book “Insect-Eating Plants” in 1876. Carnivorous plants have evolved to specialize in particularly nutrient-poor soils and hostile environments such as swamps and bogs. Nevertheless, like all plants, they are dependent on growth-relevant nutrients such as nitrogen, phosphate and potassium. However, they have to eat them by attracting, catching and “eating” small organisms such as insects. The natural scientist Darwin saw this type of ecological adaptation as proof of his theory of evolution.

Carnivorous plants can be found all over the world. But not only on distant continents such as Africa, Australia or the entire American continent – some carnivores (Latin for “carnivores”) are also native to Europe. Various sundew species (Drosera) and butterwort species, for example Pinguicula vulgaris, live in our latitudes. Both genera live mainly in moist, nutrient-poor moor areas. The common water hose (Utricularia vulgaris) occurs in nutrient-poor waters. Some species can be grown as indoor plants.

Different types and catch strategies

Basically, there are three prey-catching strategies for carnivorous plants: There are folding traps like the Venus flytrap (Dionaea muscipula), sticky traps like the sundew (Drosera) or butterwort (Pinguicula) and pitfalls like the pitcher plants (Sarracenia), the cobra lily (Darlingtonia) and pitcher plants (Nepenthes). The carnivorous plants attract their prey in different ways: through an intense scent, bright colors or glittering drops of a substance that smells of nectar, but which is used to stun the prey. Carnivores, such as some sundew species, also use tentacles and trap flaps to transport their catch to the digestive system. The water hose species use a special trapping method: They use suction traps to catch small crabs and water fleas in the water.

Venus Flytrap

There are numerous different species of carnivore, most of which differ in the way they catch insects and other invertebrates. Probably the best-known representative, which is also regularly found in DIY stores and garden centers, is the Venus flytrap (Dionaea muscipula), which belongs to the sundew family (Droseraceae). Their trapping method is quite spectacular, as it forms trapping leaves with tapered bristles on the edges. The inside of the catch leaves is intensely red in color and secretes an attractant fluid that mainly attracts flying insects such as hoverflies or house flies. Furthermore, there are small trigger bristles on the inside of the catching leaves, which, if touched by an insect, trigger the rapid closing mechanism of the leaf and snap the trap shut. Both halves of the leaf close within a few milliseconds and the bristles on the edge of the leaf interlock in such a way that it is no longer possible for the captured prey to wriggle out.

After the trap is closed, the Venus flytrap uses chemical processes to check whether it is worth digesting the dead prey. If this is not the case, the catch leaf opens again, the prey falls to the ground and the catch leaf is “focused” again. If the feedback is positive, however, the plant seals the edges of the catch leaf and begins to channel a digestive secretion into it. After several days, the prey is completely decomposed and the catch leaf opens again. This process can be repeated up to five times per sheet, after which it dies.

Sundew and butterwort

There are three sundew species (Drosera): Drosera intermedia, Drosera rotundifolia and Drosera anglica. All wild species are on the red list and must therefore not be taken from nature. The growth forms and the design of the traps are different in shape and size for the species, but the trapping method is very similar. On the leaves of the sundew are tentacles that move close together, at the tips of which the plant secretes a sugary, sticky secretion. This secretion attracts insects and is so sticky that they cling to it. If a prey is caught, the nearby tentacles also bend over it, strengthening the grip and secreting digestive enzymes that slowly decompose the prey and release the nutrients it contains. If the prey is completely digested, the tentacles stand up again and the game starts all over again.

The butterwort (punguicula) catches its prey similar to the sundew. However, it has no tentacles, but secretes a sticky lure secretion from glands on the leaves, to which small insects such as mosquitoes stick. They are then broken down on the spot by digestive enzymes and converted into nutrients for the plant to absorb.

Pitcher plants, pitcher plants and pitcher plants

These carnivorous plants carry traps, which, as the respective name suggests, are shaped like a can, jar or hose. At the bottom of these vessels there is a cocktail of various digestive enzymes that dissolve the captured prey. This is attracted by the sweet smell that this cocktail exudes. If animals now reach the edge of the vessel, which is very smooth thanks to a special liquid, they can no longer hold themselves and slide inside and thus into the digestive tract of the plant, where they are decomposed. With proper care, this group of carnivorous plants can form tube traps up to a meter in length and pitchers several centimeters in size. The plants are correspondingly large – they therefore sometimes require a lot of space and a high degree of attention. Some known types are:

• Pitcher plants: Nepenthes ventricosa x inermis (hybrid form), N. truncata, N. rafflesiana
• Pitcher plants: Cephalotus follicularis
  Pitcher plants: Sarracenia purpurea, S. flava, S. psittacina

Proper care for carnivorous plants

Carnivorous plants are not very easy to cultivate as indoor plants and one should be aware of the respective requirements of the different species. The most important parameters in terms of keeping and care are humidity, nutrient requirements, light and temperature.

Humidity

Pitcher plants (Nepenthes) in particular need consistently high humidity. This is due to their natural locations (for example high-altitude cloud forests). A humidity of 60 percent is the absolute minimum here and, depending on the species, a humidity of 80 to 100 percent can be necessary for a successful culture. This is not possible in open pots, which is why these plants are usually kept in terrariums. Venus fly traps (Dionaea) and sundew (Drosera) can be kept at lower humidity, but here the minimum should not fall below 40 to 50 percent. This can become a bigger problem, especially in winter, when the air humidity drops to 20 percent or less in dry heating air.

As already mentioned, culture in a closed terrarium is a good way to achieve the required values. However, the further requirements of the plants and their subsequent size must be taken into account. For example, bug plants (Roridula) are unsuitable for terrariums because they require moving air and without it they die quickly. A water bowl filled with expanded clay, in which the actual plant pot is located, can also contribute to higher humidity through evaporation. A mist maker that uses ultrasound to convert water into a fine mist can also help. Basically, it is worth purchasing a hygrometer with which the humidity in the room or in the closed terrarium can be closely monitored.

Nutritional requirements

Carnivores require a nutrient-poor substrate and nutrient-poor (especially low-lime!) Irrigation water. You should completely avoid mineral fertilizers. Carnivorous plants usually do not tolerate normal potting soil and tap water. Use azalea soil or – even better – special carnivore soil from specialist shops. The latter usually consists of an unfertilized mixture of white peat and lime-free sand. Decalcified tap water or rainwater are suitable for watering. In the case of a terrarium planting, the use of expanded clay as drainage is recommended so that there is no waterlogging in the root area. If you have fallen in love with a plant that has even more specific substrate requirements, further fine-tuning may be necessary – however, you should be able to successfully cultivate most carnivores with this soil.

Location and light

When it comes to wild carnivorous plants rather than specially grown hybrid forms that you want to cultivate, the light factor plays an important role. The majority of the species mentioned need a lot of light, which is why it is important that the house is as bright as possible. However, some species do not like direct midday sun. An additional electrical light source may be required if necessary. The reason for the high demand for light is the natural location of the plants, which, with their hostile conditions, hardly allow any other, shadow-throwing growth. The light factor is so relevant for plants that their entire growth can change. Most plants develop a larger leaf surface when there is too little light and become lighter. If there is a lack of light, some even stop forming the typical traps and instead produce long shoots and leaves in order to get the necessary light. So always pay attention to the individual light requirements of your carnivorous plant and take changes in color and growth seriously.

Types and their light needs:

• Sunny and very light: Drosophyllum and Roridula
• Sunny and lots of light: Sarracenia, Dionaea, Byblis and Heliamphora
• Sunny and normal daylight: Darlingtonia, Cephalotus and Drosera
• Moderately sunny and normal daylight: Highland Nepenthes, Genlisea, Aldrovanda, Dwarf Drosera and some Pinguicula and Utricularia
• Partial shade and normal daylight: Lowland Nepenthes, Queensland Drosera and some Pinguicula species

A south-facing window with plenty of natural light is a good location for most carnivores. If you are cultivating plants that do not hibernate (for example Nepenthes or Heliamphora), you should ensure sufficient light supply, especially in winter. This is hardly possible in a natural way, which is why artificial light is often necessary. Set up the light source so that the daylight phase is artificially extended. Start the supply of light when the sun is already losing its strength due to its low position. This is usually the case in the afternoon from around 4 p.m. Extend the photoperiod to around 7 or 8 p.m. In principle, all plant lights with high pressure sodium vapor lamps or suitable LED light sources, which are available in various power ranges, are suitable as light sources. If you adjust the lamp to the needs of your protégés when buying, then there should be no problems with the light supply.

Winter dormancy for carnivorous plants

Some carnivores, such as the Venus flytrap, need a winter break in which to regenerate. The winter quarters should still be bright, but significantly cooler at temperatures between four and ten degrees Celsius. If you don’t have a greenhouse or the like, you can overwinter the carnivorous plant in the unheated stairwell or in the attic directly under the skylight. Make sure, however, that it is not exposed to drafts that are too cold. It also requires less irrigation water, just make sure that the root ball remains moist and avoid waterlogging. Ideally, you have provided a drainage layer and / or a permeable substrate and a pot with a drainage hole. In late spring the plant can be used to warmer temperatures again and should sprout again quickly and strongly.

Feeding carnivorous plants?

Active feeding is not necessary for carnivorous plants – so you do not have to buy a terrarium for food animals. Most of the time, suitable flying insects such as fruit flies or fungus gnats live in the apartment anyway and end up in the trap. Nonetheless, you can still help here, for example to be able to observe the catch effect live. The only important thing is that you don’t overdo it. The plants usually get along quite well on a minimum of animal nutrition. Venus fly traps in particular can only open and close a catch leaf a maximum of five times before it dies. In the case of larger prey, it can even happen that it dies during or immediately after the first decomposition.