A wide range of carnivorous plants can be cultivated successfully on the windowsill over years. Important is a species selection on the basis of the criteria listed below. If none of these criteria argue against a culture on the windowsill, the plants can be cultivated without great effort according to the following care instruction:
1. light: As much as possible, choose a light location. An additional lighting in winter is useful, but not urgent. For a north-facing window are at best uncomplicated butterwort species suitable.
2. humidity: Secondary. Species with a desired, permanent humidity >90% are anyway not suitable for a culture on the windowsill. Here is the use of a terrarium necessary. Uncomplicated species mostly accept a humidity > 60%. Critically can become winter again, if humidity due to heating all too much decreases. Then it often can be enough to put the plants in larger saucers to raise humidity due to evaporation.
3. watering: Ebb-and-flood system with lime-free water! The pots should permanently stand within one to two centimetres water. As water are suitable osmosis water, distilled water, in rural areas also rainwater. With piped water you will kill medium-term because of the salt content each carnivorous plant. Here Mexican butterwort species are the sole exception.
4. soil: Unfertilized bog peat. Almost all species can manage with this. Only a few species obligatory require another mixture, but they are anyhow unsuitable for a culture on the windowsill. An addition of some quartz sand (lime-free!) is not a bad thing, because thus soil becomes some looser, but it is not obligatory. To the soil of Mexican butterwort species you can add circa 10% loam, albeit that neither excessively boosts the growth.
5. fertilisation: Obsolete! According to studies a positive effect by a marginal leaf fertilisation lets prove. However, for this purpose you need lots of experience and an absolute instinctive feeling, because the plants respond to the least overfertilisation by dieback. Likewise the benefit by a marginal fertilisation is small. In weighing up the choices: Let it be! The situation is similar with an extra feeding with insects. Plants do not depend on this, because they do not have to prevail against competing plants in their own pot. Indoors unutilised insects easily mould especially in winter and jeopardise thereby the plants.
You should check the following criteria to select suitable species:
1. temperature: In your house obtains circa 18° – 25°C, all-the-year. At night a little less than by day. As a consequence especially species are unsuitable, which require a distinct temperature drawdown in the night to grow in the long run.
Unsuitable are: Heliamphora-species (except hybrids), highland-Nepenthes, Darlingtonia
2. humidity: Even if you mist daily your windowsill, you will not be able to keep constant humidity long-term on values > 90%. Furthermore exists the danger of mould formation. As a consequence tropical species are unsuitable.
Unsuitable are: lowland-Nepenthes, Genlisea, Queensland-Droseras, epiphytic Utricularias
3. ventilation: On your windowsill air stands still, a ventilation as outdoors does not take place. When sun is shining, the windowsill is heating up. Sometimes humidity goes up, sometimes goes down. Most species do not care about this lacking ventilation, but there are exceptions!
Unsuitable are: Byblis, Drosophyllum
4. summer dormancy: Very few species stop growing in spring and die off above ground. These species come from regions which dry out in summer. Dry period is survived by the use of tubers, from which the plants sprout anew in autumn on setting in rainfall. Meanwhile the tubers must be stored cool and dry.
Only partly suitable are: tuberous droseras
5. winter dormancy: In principle all species, which show a winter dormancy, can be cultivated all-the-year under warm conditions. However, in the long run that devitalises the plant, it becomes sickly and lazy about blooming.
Only partly suitable are: Dionaea, Darlingtonia, Sarracenia, hardy Droseras, Pinguiculas and Utricularias
Which species are suitable then?
all Droserae (except the above mentioned groups): so first and foremost South African species and pygmy species; all Pinguiculae (except the above mentioned groups): so first and foremost Mexican species, all Utriculariae (except the above mentioned groups): so nearly 200 species, Roridula, Nepenthes-hybrids, Heliamphora-hybrids