Most temperate carnivorous plants, those growing in areas with distinctive seasons, go through two distinctive phases of growth throughout the year. In the Northern Hemisphere, they generally emerge, bloom, and start throwing off their first traps in March and April, and keep growing until summer. In particularly hot areas, they go into a summer torpor when the temperature gets above 98° F (37° C) and generally stay that way until the summer heat breaks. Here in Texas, October and November bring on a whole new explosion of growth. Sarracenia pitcher plants explode with traps with brighter colors than seen through the rest of the year. Venus flytraps throw off more and larger traps. Sundews go positively hazy with the amount of mucilage their tentacles secrete. Even butterworts get fat, wide, and expansive.
It’s just a shame that none of this lasts.
Right about the end of October, anyone who’s purchased a pitcher plant or flytrap for Halloween is coming to a sad realization: they won’t be able to enjoy their plants’ company for too much longer. (Well, that’s if the purchaser lives in the Northern Hemisphere. Australian, Argentine, and Aotearoan carnivorous plant enthusiasts are seeing their plants first bloom around then, but then they’ll have the same disappointment in April.) That display of color and form is a last gasp for the season, an attempt to capture a few last insects before going dormant.
To understand why temperate carnivores go dormant, let’s take a look at the situations under which most of them live. The common factor with almost all carnivores is that they’re extremely slow-growing compared to other plants in their native habitats. Carnivorous plants don’t choose to capture and digest insects and other small prey to be perverse: they capture prey for what nitrogen and phosphorus they can get, which gives them a strategic advantage in areas where other plants can’t get enough of both elements for survival. The traps take a lot of energy to grow, and young traps on seedling carnivores usually aren’t effective at capturing much of anything. A typical flytrap, for instance, might need as much as three years to grow to a decent size. Tropical carnivores can do this by growing all year around, but away from the equator, winter gets in the way.
To get a good idea of the general weather conditions faced by most temperate carnivores, let’s take a look at those conditions in northern Florida. The area around Tallahassee and Panama City is one of the richest carnivore habitats on the planet, with at least five species of Sarracenia, five species of sundew, four of butterwort, and eight of bladderwort, and even a possible relict population of Venus flytraps in Apalachicola National Park south of Tallahassee. By the end of October, the weather tends to slide from the usual “balmy” to downright chilly, and the area is already catching its first serious frosts and sub-freezing weather by the end of November. The Florida Panhandle doesn’t get much snow, but it’s been known to get a few centimeters from time to time, and it definitely gets cold enough that local plants need a strategy to survive the admittedly short winter.
Now, that’s northern Florida, with the warm Gulf of Mexico nearby to buffer temperature extremes. Most species of Sarracenia range further north, into Georgia, and the Venus flytrap is native to the northern portion of North Carolina. Several species of sundews may be found further north than this, on both sides of the Atlantic, and the butterwort Pinguicula vulgaris can be found ranging into northern Europe and Canada. (I’ve personally observed P. vulgaris near the summits of mountains in the Canadian Rockies, so I can attest to their being some of the toughest carnivores I’ve ever encountered.) Even the purple pitcher plant, Sarracenia purpurea, ranges from the Gulf of Mexico up the east coast of North America into Newfoundland and Labrador (where it’s the provincial flower), and west into Michigan and Ontario. Considering that these carnivores don’t grow quickly enough to produce seed and die before winter arrives, how do they survive to spring?
Well, they do so by building up reserves during the growing season and then shutting down before the frosts can cause too much damage. With pitcher plants, the plants stop growing new traps and produce purely photosynthetic leaves called phyllodia, which continue to catch as much light as is available until they die off from frost. Aquatic bladderworts produce bulbs called turions, which sink into the mud and wait out the winter. Both butterworts and sundews die back to nodules right at the soil line, just in time to be covered with leaves or snow. For the rest of the winter, they sit back, and wait.
Finally, when temperatures start to rise at the beginning of spring, the plants start to stir. With pitcher plants, in order to prevent the capture of potential pollinators, the awakening plants take the last of their reserves and use the energy to grow bloom spikes. This is carefully timed, so that the blooms are already pollinated by the time the first traps start to grow. With sundews, butterworts, and bladderworts, they also produce bloom spikes, but their blooms attract a completely different variety of pollinator than they attract prey. While the leaves of butterworts and sundews snag fungus gnats and mosquitoes, the blooms draw moths, butterflies, and hummingbirds. Either way, the flowers receive pollen, and the plant returns to capturing prey in order to have the energy to produce a full complement of seeds.
Now that you understand the basics of dormancy, it’s a matter of understanding the whys. When a carnivore goes into dormancy, it should go into a complete dormancy. Any ongoing growth during the winter is at the expense of spring blooms, and if the plant doesn’t have enough energy left after blooming, it may die. The conventional wisdom for raising Venus flytraps is to snip bloom spikes before the flowers open, which makes sense with a newly purchased plant: it never had the opportunity to collect enough starches and nitrogen to stand a chance. If given a good summer with plenty of light and a suitable rest, it should be ready for blooming the next spring, but an inadequate dormancy, or no opportunity for dormancy at all, and the poor plant is running on fumes.
During the spring of 2008, I had a firsthand experience with the stresses facing a carnivore with an inadequate dormancy. I had a beautiful Sarracenia purpurea pitcher plant rescued from a home improvement center the autumn before, and I let it sit outside and die back over the winter. Come spring, it produced one gigantic bloom and about three pitchers, and then it died a month later without warning. Attempting to reproduce and grow at the same time, it couldn’t do either.
Enough with the warnings. For those who live in temperate climates, setting up dormancy is easy. Simply leave the plant outdoors starting at the beginning of autumn, so the plant slips into its rest based on light and temperature. In areas where the local winter temperatures go well below freezing, they’ll need some protection, and plants in bog gardens need to be mulched well to insulate them. For plants in pots, put them in an unheated area such as a garage or shed, or at the very least on the southern side of a house or wall to protect them from the northern wind, and cover with a plant blanket if necessary. After this, check them regularly to make sure that they’re properly watered, but otherwise leave them alone.
Thanks to the wonders of modern transport, many carnivores appear in markets where they’d never survive in the wild. In places where the winter temperatures never get to freezing, much less below it, it’s necessary to simulate a good solid winter. In this case, remove the plant from its garden bed or pot, gently remove the soil from its roots, and wrap the roots with long-fibered sphagnum moss soaked in rainwater or distilled water. Wrap the moss with plastic cling film, cut back the plant to its central leaves with sterilized clippers, put the whole plant in a plastic bag, and put it into a refrigerator. DO NOT PUT THE PLANT INTO A FREEZER, no matter what. For those with the option, try to use a refrigerator reserved solely for use for plants, if only to prevent contamination of food with sphagnum moss. If not, at least mark the bag with the date in which it should be removed from the fridge.
And when should you take your plants out into the light? It honestly depends upon the area, the species of carnivore, and the temperatures during dormancy, but I stick to a hard and fast rule based on American holidays. I always put my carnivores into full dormancy the weekend of American Thanksgiving, the last Thursday of November, after allowing the plants to acclimate to lessened sunlight and lowered temperatures. Other than making sure that they don’t dry out over the winter, I don’t touch them until St. Patrick’s Day, on March 17. In Texas, the threat of killing frost is generally past by then, and pitcher plants and sundews promptly start blooming shortly thereafter.
With a bit of preparation and a bit of skill, there’s no reason why a temperate carnivorous plant can’t live and thrive for years so long as it gets its annual winter slumber. If you can deal with not being able to gaze upon its beauty before spring, the resultant explosion of blooms and traps is worth the wait.