Overwintering Carnivorous Plants
Over Wintering Carnivorous Plants
It's a good idea to provide winter protection for your carnivorous plants. You have put a lot of time, energy and money into your bog garden, and protecting your investment is worthwhile. Many outdoor growers often have more than the carnivorous plants and bog companions that are native to their area. You will find that most carnivorous plants can be grown well north or south of their endemic range, but in so doing, you may find that they are stressed by their new seasonal extremes. Keep in mind that temperate carnivorous plants that normally grow in cold and/or freezing winter temperatures require a winter dormancy period. Another important consideration is that winter time can be a very dry season. It sounds contrary at first, but consider that ice does not make free water available to plants. Winter heaving can also be destructive. It occurs when periodic freezing and thawing pulls the plant out of the ground.
For indoor growing temperate plants, I like to target 45 days at 45°F (7°C). This can be accomplished several ways. Place the potted plant(s) in a basement, garage, under a deck or on a protected porch where temperatures are less severe. You could also bare-root the plant, remove the traps and most of the roots and store them in a plastic bag in the crisper drawer of the refrigerator. Wrap them in moist sphagnum or peat first and poke holes in the bag for some air circulation. When I taught high school Biology, I would often do this for the plants in the summer time, to "fool" them into a winter rest mid-summer, and them replant them in the fall, so they were actively growing during the school year. Remember to provide winter moisture. The soil should be moist, but not saturated like it is in the growing season. Check on them periodically during the winter rest. If you see signs of growth it's certainly time to bring them out into typical carnivorous plant growing conditions.
For outdoor growing potted plants, if they are in large enough pots, greater than 16" (40 cm), they might be fine, but smaller pots will certainly suffer from winter burn from wind and freezing temperatures. No matter the size of the pot, it's still a good idea to treat them like indoor growers, as described above, especially if they are in small pots. If you choose to keep them outdoors try digging a hole and burying the pot up to its soil surface level, and mulch them, as described below.
For outdoor growing, I prefer to grow carnivorous plants in garden bog beds or inground boxes. Being within the ground helps moderate the winter temperatures. In my 50 years of growing carnivorous plants, I have found that it really doesn't matter how cold it gets, as much as, how fast it gets cold. You want to moderate the temperature fluctuation so that there are more gradual changes and you avoid unseasonable thawing. Here at Carnivorous Plant Nursery in the Catoctin Mountains of Western Maryland, winter temperatures of -9°F (-23°C) are not unusual, and our plants do fine, even the more southern forms like S. purpurea venosa, S. minor, S. psittacina, S. alata, and our Dionaea. Though snow itself can be a natural mulch, it is not reliable for winter protection. I use 2 different overwintering methods, depending upon the growing situation. My favorite is mulching with 6+" (15+cm) of pine needles. I use pine needles instead of leaves because some, like oak, can mat up making an impermeable layer that harms the plants. I will place a sheet of burlap down first, with the mulch on top. This makes spring removal much easier and neater, because all that I have to do is lift and shake the burlap to remove the mulch. I will top the pine needles with bird netting, anchored down with lawn staples to help keep the mulch in place. For our larger growing beds I use winter horticultural fabric. This is white, porous, like felt, and allows light and moisture to penetrate. It's available in several grades. I typically use several layers, which typically keeps temperatures 10 to 20° above ambient temperatures. It can be used several winters over. Keep an eye out for mice, voles and other creatures which may find a haven and food stocks in the mulched beds. I have used cubes of rat poison on the plants under the mulch to reduce winter rodent damage, but I do not do this if water could drain into natural water sources.