Growing carnivorous plants indoors all year

Choose plants that suit a house

Indoor success starts with the plant list. A house has less light than most carnivores want, dry winter air near the windows and no real winter, so some plants are much easier than others.

For Nepenthes, the ICPS window sill page adds that lowland species with thick, leathery leaves cope best with low humidity, naming N. rafflesiana, N. bicalcarata and N. truncata, and that highland species from outside fog forests, such as N. alata, N. khasiana and N. ventricosa, handle cool winter rooms ^[3]. If you want a cold temperate sundew in a terrarium, the ICPS suggests tropical forms instead, such as D. intermedia from Cuba or Venezuela or the Hawaiian D. anglica ^[12]. For the classic houseplant butterwort, see the Mexican butterwort profile.

Light: the deciding factor

A typical windowsill does not give a Venus flytrap enough light ^[1]. The checklist’s target of at least six hours of direct sun is hard to reach in a house; it suggests a desk lamp with a standard white LED spotlight, on for 12 to 16 hours a day ^[16]. For year-round indoor growing the ICPS gives 15,000 to 25,000 lux of white LED light for about 14 hours a day ^[1]. The numbers by genus are in light, and the grow-light calculator scales them to your shelf.

Windows have their own problems. In heated houses the radiators and vents are usually under or beside the windows, so plants alternate between cold drafts off the glass and warm, dry air, and the ICPS author has had Nepenthes growth tips killed by window drafts in winter ^[3]. The NYBG similarly advises keeping flytraps away from heating and air-conditioning vents and drafty windows; normal room temperatures of 65 to 75 °F (about 18 to 24 °C) suit them ^[17]. Most butterworts turn their flowers toward the window, so the ICPS suggests rotating pots, or growing P. gigantea, whose flowers do not bend toward the light ^[3].

A year-round setup for Venus flytraps

The CPN article “Grow Venus flytraps indoors” describes one complete method, which its author presents as what works for him rather than the only way ^[2]:

• Pots. 8 cm square by 9 cm tall pots in standard plant trays, or 10 cm square by 12 cm tall pots for several plants. Larger pots hold moisture longer if a tray dries out.
• Soil. Roughly 50:50 washed peat and coarse silica sand, with the bottom of the bulb and roots in the mix and about 2 cm of pure sand on top, so most of the bulb stays out of wet soil.
• Water. Trays with 1 to 2 cm of water, or topped up to about 3 cm when dry, and no top watering except at repotting. Pure water such as reverse-osmosis or rain water.
• Light. At least 15,000 lux, better 25,000, for about 14 hours a day, from 3000K LEDs with a color rendering index of 90 or more.
• Food. Rehydrated freeze-dried bloodworms whenever growth slows.
• Repotting. Every year or two, with fresh soil each time.

All of the above is from the article ^[2]. The ICPS guide shows flytraps that have grown indoors under lights this way for more than 10 years ^[1]. Detail on each element is in water and feeding.

Seasons indoors

Flytraps do not need seasons to grow well. The ICPS LED page notes only that they flower together if they get seasonal light cues ^[18]. The CPN author’s plants in the house, under 15 hours of light a day, do not slow down in winter, while those in his garage on a timer that follows sunrise and sunset slow down but never go fully dormant ^[2].

Other plants depend on seasonal cues indoors:

• Mexican butterworts need slowly changing day length; under continuous light they get stuck in their non-carnivorous winter form ^[5]. The ICPS says a windowsill is the best place for them if you have no greenhouse, because the light cues are hard to give in a terrarium ^[3].
• Sarracenia expect seasons. The ICPS author has had plants moved from lights to the outdoors get “confused” and not grow for a year ^[19], and the LED page advises timers set to local sunrise and sunset so plants stay in phase ^[18]. The NYBG suggests 8 to 10 hours of artificial light in winter and 16 to 18 in summer, and says most indoor pitcher plants need a winter dormancy with lower temperatures and less water ^[7].
• Pygmy sundews and Cephalotus grow under constant light but do not make gemmae or flowers ^{[8, 11]}.

The ICPS also advises against bringing outdoor flytraps indoors under lights for winter only, unless the timer follows local day length ^[1]. See dormancy for the full picture.

Humidity, water and pests in a house

Most carnivorous plants need less humidity than people expect. Flytraps do not need a terrarium; plants raised in greenhouses or sold in plastic cups take a while to adjust to drier air, but they do adjust ^[16]. Heliamphora are the clear exception and need an enclosure unless the room’s humidity is above 70% ^[10]. The details are in terrariums and humidity.

Dry indoor air empties trays quickly. The CPN author refills open trays every other day in his low-humidity house, which is one reason he uses leaky terrariums ^[2]. Nepenthes in a house use much more water than in a greenhouse, so the ICPS suggests larger pots and a heavier mix of about 75% long-fiber sphagnum to 25% perlite ^[3].

Indoor plants rarely catch anything, which is why manual feeding with bloodworms suits them ^[20]. Fungus gnats are the usual indoor pest; a layer of pure sand on the soil helps, since it does not attract them ^[2], and the ICPS puts up to 5 mm of coarse sand on butterwort pots for the same reason ^[5]. See fungus gnats. Cephalotus is prone to mildew: the ICPS describes plants near an open window that developed it when their humidity dome was removed ^[11].

Mistakes the sources warn about

• Counting on a dim window for flytraps and other full-sun plants ^[1].
• Leaving a new flytrap in its plastic cup, which the ICPS says can harm it ^[16].
• Putting indoor flytraps in the refrigerator, which the ICPS calls a waste ^[1].
• Growing tall Sarracenia under top lighting only ^[4].
• Keeping seasonal plants under a fixed day length, such as Mexican butterworts and Sarracenia ^[18].