A regular question at Triffid Ranch events and shows involves the notice on the ID tags for North American pitcher plants and Australian triggerplants: “Put into dormancy in winter.” Quite understandably, this concerns beginning carnivorous plant keepers, because “put into dormancy” implies all sorts of laborious and detailed activities that they may or may not have time to do. Many online guides to carnivorous plant care recommend a full dormancy period in winter, but don’t give much in the way of details. Others go well into overload, and yet others instill a near-panic about dormancy. The other questions involve which plants require a winter dormancy, which ones wouldn’t mind a good nap, and which ones don’t need it at all. And to make it even more complex, a few popular carnivores need a summer dormancy instead of a winter dormancy, waiting until things cool down to reach their full potential.
To distill it down to basics, dormancy is when perennial flowering plants shut down or slow down during winter to conserve energy and store energy for future growth. By way of example, roses lose their leaves in winter but continue to photosynthesize through their stems, resprouting new leaves each spring. Irises spend the winter catching as much light as possible while the weather holds, storing the captured energy in the form of starch in rhizomes below the soil surface and resuming growth and blooming after the last risk of freezing. Tulips and daffodils spend the year catching light and then die back to bulbs in autumn to wait out winter. A majority of carnivorous plants use the same strategies to get through potentially harsh winter weather, with the main difference being that carnivores require a lot of energy to produce traps, nectar, adhesive if applicable, and digestive enzymes on top of the energy needed for blooming. This is why many species need a dormancy over the winter, so they can focus on energy storage and not on new growth or on digesting captured prey. Even tropical species that don’t require a dormancy won’t mind a shortened photoperiod, which gives them time to catch their metaphorical breaths and save a bit of energy for their next big growth spurt.
(A little sideroute. When carnivorous plant people talk about “temperate” versus “tropical” plants, they’re talking about plants that live in areas that get down to or below freezing in the winter versus plants that live in areas where the temperatures never get below 50F/10C. Temperate plants include North American pitcher plants (Sarracenia spp.), Venus flytraps (Dionea muscipula), English sundews (Drosera anglica), and common butterworts (Pinguicula vulgaris). Tropical species generally include Asian pitcher plants (Nepenthes spp.), Mexican butterworts (Pinguicula spp.), and most Australian sundews, particularly Drosera adelae. Many genera of carnivores, particularly sundews, butterworts, and bladderworts, have species that run the gamut from near-Arctic to equatorial, so knowing which species is which can be really important to keeping a particular plant alive. Each group has different requirements or requests, but usually don’t require a lot of care during that dormancy other than light and regular waterings.
(Another sidenote. If you’re just starting with carnivorous plants, or you know someone who is, odds are pretty good that you or they started with a prepackaged carnivorous plant ensemble. These usually arrive in garden centers or home improvement centers with a Venus flytrap, a North American pitcher plant, and either a sundew or a butterwort, but sometimes with tropical species such as Asian pitcher plants mixed in. In the Northern Hemisphere, the end of October is a good time to separate these and put them in several different pots: some may get along well together, but keeping flytraps with Sarracenia usually doesn’t turn out well, and keeping flytraps with Nepenthes is a good way to kill one or the other or both. If you know that a group of plants thrive together in the wild or in captivity, leave them alone, but often it’s better to separate them for everyone’s sake.)
The next question that comes up is “How long should keep my plant in dormancy?” Here in North Texas, I generally tell Americans “From Thanksgiving to St. Patrick’s Day,” translating to “from the end of November to the middle of March” for everyone else. Around here, those dates pretty much mark the beginning and the end of freezing weather, although we have been known to extend that on either side a bit. Obviously, at higher latitudes, freezing weather will hit a lot sooner in the year, so check for your area’s frost zones. The big thing to remember is that dormancy is encouraged more by a shortened photoperiod than the temperature itself, so try to protect your plant or plants from streetlights or other lights that might throw that off.
Still confused? The following are guidelines based on 20 years of carnivorous plant growing in the North Texas area, and may be modified for your particular area and conditions. (Disclaimer: these are recommendations, and the Texas Triffid Ranch takes no responsibility for loss or damage caused by anomalous weather conditions or other factors outside of the gallery’s control. All readers follow these guidelines at their own risk.) The one absolute on every group is to make sure to keep your plants at least moist through the winter. If it dries out, it almost always won’t come back.
Outdoor Temperate Plants
With plants best kept under full sun under temperate conditions, such as Venus flytraps and North American pitcher plants, trim off any dead leaves or traps and keep them outside. If your area gets strong prevailing winds in winter, try to protect your plants from the wind, as it will dry them out, but otherwise leave them in full sun and keep them moist all winter. If temperatures get especially cold (below 20F/–7C), cover them with plastic sheeting or an old bedsheet for the duration, but remove it when the worst of the cold is over. If the particularly cold period lasts less than a week, don’t worry about the plants, but keep an eye on the pot or container in which the plants reside, as these can and usually will be damaged by long periods of subfreezing temperatures. For subfreezing temperatures lasting more than a week, the plants can be brought inside temporarily (try to put them in places with plenty of light but temperatures cooler than room temperature, if possible, such as mud rooms or laundry rooms with outside windows), and move them back outside as soon as the risk of severe temperatures is over.
Also, while most outdoor carnivores will keep green traps or leaves going, Australian triggerplants have a tendency to go scruffy by late October and then die back entirely by December. Do NOT throw them out, as they come back from their roots in spring. This goes double if the plant appeared to die after a massive freeze: if anything, a good solid freeze seems to encourage lots of blooms.
A special note: if you keep your plant in a ceramic container with a lot of sentimental or other value, moving the plant temporarily to a plastic container over the winter is very highly recommended. The water in the plant’s substrate can and will expand and split or chip the pot, especially in narrower pots.)
And a side discussion on refrigerators. A lot of older print guides suggest that for folks living in areas that don’t get cold enough to set off dormancy, rhizomes and bulbs can be uprooted gently, wrapped loosely in wet long-fiber sphagnum moss, and put in the refrigerator. Since that prevents the plant from getting light during the winter, this should be kept to a minimum, but it IS a good way to store Sarracenia rhizomes, leaves cut off first, until spring planting. Whatever happens, do NOT put your plant in the freezer unless you’re really bored with frozen spinach and want a new taste experience.
Outdoor Tropical Plants
If you happen to live in an area with high humidity but where temperatures go below 50F/10C, tropical carnivores such as Nepenthes pitcher plants will need to come inside over the winter. Over the winter, they’re best kept in high-humidity areas (bathrooms are usually perfect for this, especially with multiple people using the shower in the morning) with either a lot of light through windows or artificial light. Barring that, to deal with how dry most houses are in the winter, look into either a mister or ultrasonic fogger blowing mist or dripping onto the plants through the day. Honestly, a combination of natural and artificial light is best, but try to keep the latter to about 8 hours a day, matching the light outside as best as possible. This won’t guarantee blooms in spring (or, in the case of Mexican butterworts, blooms in late winter), but it should encourage them. When the low temperatures outdoors get high enough in spring to move your plants back outdoors, do so carefully by letting it acclimate to full sun gradually over the space of a couple of weeks. Do NOT just put it out in the sun without acclimation unless you want a critically sunburnt plant.
Indoor Temperate Plants
Several carnivores commonly offered for sale, such as Cape sundews (Drosera capensis), primrose butterworts (Pinguicula primulflora), and Australian pitcher plants (Cephalotus follicularis) are adapted to colder temperatures but don’t necessarily need a full winter dormancy. They won’t mind a good rest, though, and cutting back on their hours of light over the winter may encourage a blooming response in spring. This is especially true of South American pitcher plants (Heliamphora spp.), which love cooler temperatures anyway and bloom enthusiastically in spring if given a good real or simulated winter. Follow the advice for outdoor tropical plants above for light scheduling, and try to keep them in the cooler parts of the house or office if possible.
Indoor Tropical Plants
For Nepenthes pitcher plants, tropical sundews, tropical bladderworts, and other carnivorous plants already being kept inside, just keep doing what you’re doing if it’s working. If you want to encourage blooming, switch to a shorter photoperiod, but otherwise a 12-hour on/12-hour off cycle works beautifully. In addition, feel free to mist your plants more heavily during the winter months: not only will this compensate for heaters or other factors lowering the indoor humidity, but it sometimes encourages new growth and blooming by making the plant think that it’s in the middle of monsoon season.
Finally, there’s the last big question regularly asked: “And what happens if you miss your dormancy period?” If you get a Venus flytrap as a gift in mid-winter and putting it outside just simply isn’t an option, don’t kill yourself. If anything, keep it inside under lights over the winter so it can hit the ground running in spring, but follow a dormancy regimen the next fall. Flytraps are an extreme example, but as a rule they can live through one winter without dormancy but won’t live through two. Does that help?