Nepenthes not making pitchers: light, humidity and age

How a pitcher forms, and what is normal

A Nepenthes pitcher is part of the leaf. The midrib runs past the end of the leaf blade as a tendril, and the pitcher develops at the tip of that tendril ^[2]. A leaf can therefore be fully formed even when its pitcher fails. NC State Extension names low humidity as one reason pitchers fail to develop properly or die back ^[2], and a CPN article cites an early report that pitchers turn brown and hard before developing when temperatures are too low ^[3].

Some gaps are normal and need no fix:

• A plant that is settling in. Rooted cuttings are weaned gradually from a sealed bag to lower humidity ^[5], and the 1987 CPN author kept new arrivals in a clear plastic bag until they stabilized ^[3].
• Winter by a window. The ICPS author lost Nepenthes growth tips to cold drafts from double-glazed windows and gave up expecting new pitchers from those plants in winter, though the plants survived ^[6].
• A vine that has started to climb. Nepenthes are climbing vines and become leggy with time; growers cut them back to bring on new basal shoots, and Longwood Gardens prunes for the lower pitchers this growth produces ^{[3, 7]}.

When a healthy-looking plant keeps producing bare tendrils in spring and summer, look at the causes below. The troubleshooter covers the same ground in short form.

Light too low

How to check. The ICPS lighting table rates Nepenthes as moderate-light plants, needing about 8,000 to 15,000 lux of white light, with lights on 12 to 16 hours a day ^[1]. Its Nepenthes guide recommends a window that gets some direct sun for house plants ^[4]. A plant in a room lit only by indirect daylight or ordinary lamps falls well short; the ICPS puts typical office lighting at about 1,000 lux ^[1].

What to do. Move the plant to a window with some direct sun, or add a white LED. The ICPS notes that an LED spotlight works over a Nepenthes because the leaves are held out more or less horizontally ^[1]. Species from very sunny habitats may need more than the average; the ICPS windowsill page flags light as a factor for species that grow in full sun in the wild ^[6]. See light and the grow-light calculator.

Humidity too low

How to check. This is where the sources disagree most, and the disagreement is useful. A 1987 CPN article on growing Nepenthes under lights called humidity essential to good pitcher formation and said most homes are too dry to allow it; its author kept plants at 55 to 65% humidity in a growing chamber and put struggling plants into a sealed plastic bag for a while ^[3]. Longwood Gardens keeps its Nepenthes houses above 80% humidity ^[7]. NC State Extension also warns that pitchers will not develop properly, or will die back, when humidity is too low ^[2].

The current ICPS guides are more relaxed. They say species and hybrids with thick, waxy leaves make good house plants in a window with some direct sun ^[4], and that lowland species with thick, leathery leaves that grow in partial sun stand up best to low humidity ^[6]. The two views are compatible if you match the plant to the room: tough-leaved plants cope with house air, while thin-leaved species need the extra humidity the older article describes.

What to do. Keep the plant away from heater vents; the ICPS points out that in winter, plants by a window alternate between cold drafts and dry blasts from the heating ^[6]. For thin-leaved plants, use a terrarium or a growing chamber. Indoor plants also dry out faster, so the ICPS suggests a heavier medium than in a greenhouse, such as 75% long-fiber sphagnum and 25% perlite, in larger pots ^[6]. See terrariums and humidity.

Too cold, or cold drafts

How to check. How cold does the plant get at night, especially near a window? Growers divide Nepenthes by the minimum night temperature they need. In the 1987 CPN article, warm growers needed at least 65 °F (about 18 °C) at night, intermediate growers tolerated 55 to 65 °F (about 13 to 18 °C), and cool-growing highland species needed nights below 55 °F. The same author reports that his intermediate plants were unharmed by seasonal nights of 55 to 60 °F as long as days reached 70 °F (about 21 °C), but that weeks in an unheated basement below 60 °F cost him nearly half his collection, with lowland N. ampullaria and N. rafflesiana the most sensitive ^[3]. Longwood Gardens keeps nights above 17 °C (62 °F) in winter and days above 22 °C (72 °F) ^[7].

What to do. Move plants back from cold glass in winter ^[6], and match the plant to your temperatures. NC State Extension gives lowland species a range of 70 to 95 °F (about 21 to 35 °C), and highland species 75 to 85 °F (about 24 to 29 °C) by day with nights in the low 60s °F ^[2]. The ICPS suggests highland species from outside the fog forests for houses, because cool winter temperatures do not trouble them ^[6].

A plant that does not suit house conditions

How to check. What kind of Nepenthes is it? The genus is enormously varied: species grow on beaches, in hot lowland forest and on cold, windswept ridges, and some like intense sun while others live in dense shade ^[4]. Not every species suits a living room.

What to do. For a house, choose a forgiving plant. The ICPS names vigorous complex hybrids such as N. x Superba and N. x Mixta as the easiest ^[4]. For windowsills it suggests N. rafflesiana, N. bicalcarata and N. truncata among lowland species, and N. alata, N. khasiana and N. ventricosa among highland ones ^[6]. See the Nepenthes genus page and the N. ventricosa and N. alata profiles.

A young, newly moved or recently propagated plant

How to check. Did the plant arrive recently, get repotted, or lose its top to a cutting? Stem cuttings can take anywhere from a month to a year to root, and cutting the growing tip out of a basal rosette often sets the parent plant back by half a year to a year ^[5]. Plants grown from seed take three to five years to reach display size ^[4].

What to do. Be patient while the plant re-establishes. The ICPS weans rooted cuttings to lower humidity in a terrarium or partly opened bag rather than moving them straight into open air ^[5]. See Nepenthes stem cuttings.

A long vine with little new growth at the base

How to check. Has the plant become a long, leggy stem? Nepenthes are climbing vines ^[3]. Longwood Gardens prunes its plants often to stimulate basal growth that produces the lower pitchers, which it finds more attractive than the upper ones ^[7].

What to do. Cut the vine back. The 1987 CPN author cut stems back to under 15 cm (6 in) once they reached 30 to 60 cm (1 to 2 ft), which stimulated new basal shoots ^[3]. The ICPS describes clipping the climbing stem to leave the basal rosette, or laying the pot on its side so a long stem hangs down until a new rosette sprouts, and rooting the removed stem ^[5].

Keeping pitchers coming

• Give moderate to bright light: about 8,000 to 15,000 lux, or a window with some direct sun ^{[1, 4]}.
• Match humidity to the plant: thick-leaved hybrids in the house, thin-leaved species in an enclosure ^{[6, 3]}.
• Keep nights above the minimum for the plant’s group and move plants back from cold glass ^{[3, 6]}.
• Prune long vines to encourage basal growth ^[7].

For indoor setups generally, see growing indoors.