Problems and what causes them
Most problems with carnivorous plants come down to a short list of causes. Each page starts with what is normal, then works through the likely causes one at a time, with what to check and what to change.
For most carnivorous plants
Aphids, mealybugs and scale on carnivorous plants
Aphids gather on new growth and flower buds and leave flytrap leaves deformed; mealybugs show up as white, cottony fluff in the crowns and leaf bases of Sarracenia and Nepenthes; scale insects look like small bumps that never move. For mealybugs the ICPS prefers weekly swabbing with 70% rubbing alcohol and a few drops of dish detergent, and warns that some insecticides kill or deform carnivorous plants. Quarantining and inspecting new plants prevents most infestations.
Fungus gnats in carnivorous plant pots: risks and control
Adult fungus gnats are a nuisance, but their larvae damage seedlings, roots and butterwort leaves that touch wet peat, and they can spread root fungi. The ICPS answer is a layer of coarse horticultural sand about 5 mm deep on the soil surface, which discourages adults from laying eggs, with seedlings kept in plastic bags until they are big enough for sand. For an active infestation, the ICPS calls Bti, a bacterium toxic only to fly larvae, relatively safe as a soil drench; follow the product label.
Gray mold (Botrytis) on dormant flytraps and pitcher plants
Fuzzy gray growth on dead or dying leaves in winter is usually gray mold, Botrytis cinerea, a fungus that lives on dead plant tissue and spreads by airborne spores, especially in cool, humid conditions. The ICPS warns that old leaves kept out of the weather in winter reduce air circulation and invite fungus, and recommends cutting back stored long-pitcher Sarracenia in fall. Remove dead tissue, keep air moving and avoid condensation; cold slows Botrytis but does not stop it, even in a refrigerator.
Mineral burn from tap water, salty soil and fertilizer
Carnivorous plants come from nutrient-poor habitats and can be killed by water with moderate or high dissolved solids, by fertilizer and by ordinary potting mix. The ICPS accepts tap water only below roughly 90 to 100 ppm total dissolved solids; above that, use distilled, reverse osmosis or rain water, since filtering and softening do not remove the salts. A plant that is already affected needs clean water and fresh, unfertilized soil.
Rhizome and root rot in carnivorous plants: causes and rescue
Rot usually follows stress: a pot that keeps the base soggy, roots burned by salty water or fertilizer, or a freeze on plants that were not fully dormant. Weak soil fungi then spread from dead tissue into living tissue, so the ICPS advises isolating the plant, cutting away every soft or brown part and repotting in fresh mix. Some infections, such as Cylindrocladium in Sarracenia, kill a plant within days and have no cure, which makes prevention the real treatment.
Weak color and floppy growth in carnivorous plants: light and other causes
Too little light is the usual cause. The ICPS rates flytraps, most sundews, Sarracenia seedlings, Cephalotus and Heliamphora as intense-light plants needing about 15,000 to 25,000 lux for 12 to 16 hours a day, while typical office lighting is about 1,000 lux. Shaded Sarracenia make smaller, weaker, sometimes flat pitchers. Not all green means trouble: the flytrap cultivar 'Justina Davis' never makes red pigment, and strong sun brings out red in many plants but not all.
Venus flytrap
Venus flytrap flowering: let it bloom or cut the stalk?
A tall, leafless stalk in spring is normal: Venus flytraps flower in late spring, holding white flowers well above the traps. The ICPS checklist and the New York Botanical Garden both advise cutting the stalk off early so the plant does not spend energy on flowers, which NYBG says can reduce the number of new leaves. Letting a vigorous plant bloom is a choice, not a mistake, but flytrap flowers do not pollinate themselves, so seed needs pollen moved between flowers.
Venus flytrap traps not closing: causes and checks
A trap needs two touches of its trigger hairs within about 15 to 30 seconds, and once it has closed it takes roughly 16 to 44 hours to reopen, so a trap that ignores one poke or stays shut for a day is behaving normally. Very young and old leaves close slowly, and each trap stops working after a limited number of closures. If most traps on the plant are slow during the growing season, the ICPS points first to too little light; hunger and dormancy are the other usual causes.
Why Venus flytrap traps turn black, and when to worry
Some blackening is normal: each Venus flytrap leaf lasts only a few months, and a healthy plant keeps making new ones as the old ones die. A trap can also die after an oversized meal, and every trap can close and reopen only a limited number of times. Worry when new traps turn black before they open, when no new leaves appear, or when the base goes soft; salty soil or water, soggy soil, and too little light or food are the usual causes.
North American pitcher plants
Sarracenia pitchers turning brown: normal aging or trouble
Often it is normal: Sarracenia go dormant in autumn and their pitchers turn brown, and older pitchers die off during the season as well. The ICPS advises cutting off only the brown parts, because the plant recovers nutrients from old green tissue. Browning of new pitchers in the growing season is the warning sign; check for heat and dry air, a pot that dried out, salty water or fertilizer, and rhizome rot.
Sundews
Sundew not making dew: light, humidity, water and dormancy
Check light first: most sundews need intense light, and experiments show that shaded sundews make less sticky leaves. Dry indoor air, mineral-rich water and fertilizer are the next suspects, since added nutrients also reduce stickiness. A temperate sundew that loses its dew in autumn may simply be forming its winter bud.
Tropical pitcher plants
Nepenthes not making pitchers: light, humidity and age
Light and humidity are the usual limits. The ICPS rates Nepenthes as moderate-light plants needing about 8,000 to 15,000 lux, and NC State Extension warns that pitchers fail to develop or die back when humidity is too low. Cold matters too: an early report cited in the Carnivorous Plant Newsletter held that pitchers turn brown and hard before developing unless temperatures reach at least 70 °F (about 21 °C). Thick, waxy-leaved species and hybrids cope best with house conditions, given a window with some direct sun.