By Dauna Koval
WSU Master Gardener
Unusual, beautiful, mysterious: Carnivorous plants get their nutrients from “meat” rather than from soil. These plants evolved in wet peat bogs, where most of the nutrients they needed had been washed out of their reach. Thus, they developed several ingenious ways of getting nutrients from what was available: primarily insects.
A more proper name for carnivorous plants might be “insectivores,” as their traps are designed to gather insects, of which they only need one or two per month. Two botanical families of flowering insectivore plants contain local native varieties: Droceracea (the sundews and the Venus flytrap) and Sarracenia (the pitcher plants).
Many of us are familiar with Venus flytraps, Dionaea muscipula (Latin for “Diane’s mousetrap”). Specialized leaf traps lie in wait like open hands that snap closed, trapping an insect as it wanders over the leaves looking for the source of a sweet smell. As the insect brushes hairs on the leaves, an electrical impulse is triggered that changes the water pressure in the leaves, causing them to close. As the insect struggles to escape, it continues to move the hairs, which tighten the leaves and cause the release of digestive enzymes. The soft parts of the insect body are dissolved and the plant absorbs the nutrients. The trap then blackens and falls off.
The sundews (genus Drosera, some of which are native to the Pacific Northwest) have traps consisting of mobile tentacles, each with a tip covered in hairs that exude a thick, sticky liquid that the insect mistakes for nectar. As the insect contacts the leaf, it becomes stuck in the glue, which covers the insect as it struggles. This effectively smothers it. In some varieties, leaves curl over the insect like a jellyroll, bringing more hairs in contact with the insect.
The North American pitcher plants (genus Sarracenia) take a more passive approach to insect capture. The pitchers are composed of a rolled-up leaf topped with a lid-like structure. The lid produces nectar and is brightly colored, especially in the UV spectrum visible to insects. As an insect seeks the nectar on the underside of the lid, it meets a waxy covering on the lip of the pitcher that causes it to fall inside. The pitcher is filled with a fluid containing the digestive enzymes. It also often is lined with hairs pointing downward, making it impossible for an insect to climb back out. I once cut open a dried-up pitcher and found the crusty remains of several insects inside. Get out the microscope!
Venus flytraps are native to North and South Carolina, which gave rise to the thought that insectivores need heat and humidity to thrive. I remember my first flytrap came with a plastic dome with instructions to place it in a window with bright direct light and to water well. Now I know it most likely died from too much heat and the chlorine in the tap water.
Although flytraps, sundews and pitcher plants do prefer the wet “feet” and dry “shoulders” they get in bogs, and they do develop better color in bright sunlight, they don’t need tropical heat. Some sundews and pitcher plants are native to our area; they and flytraps do just fine in our climate. All three need a cold dormancy period in the winter and can survive mild, short freezes.
Swanson’s Nursery in Seattle recommends these growing steps:
• Keep wet all the time. Plant in soggy/boggy soil, and water preferably from below.
• Use mineral-free water. Rainwater is best, but distilled water works too. The chlorine and fluorine of tapwater are particularly bad.
• Use mineral-free soil. A mix of sphagnum peat moss and horticultural sand or perlite is great.
• Provide lots of light. Most need at least six hours of direct sunlight per day; the more the better. However, avoid northern light and sudden increases in temperature. (The little plastic domes create a greenhouse effect of too much temperature and air humidity.)
You can purchase plants and get more information from your local nursery.
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Join the WSU Master Gardener Program. A new class to learn the elements of the program begins in January. Email 2018mgtrainees@gmail.com if you are interested or would like more information.
Dauna Koval is a WSU Master Gardener, Class of 2016. Her introduction to insectivorous plants was with a Venus flytrap gift. She is currently building some bog garden containers for her new collection of native pitchers, sundews and flytraps.
(Courtesy WSU Master Gardeners) Sundews have traps consisting of mobile tentacles, each with a tip covered in hairs that exude a thick, sticky liquid. The insect mistakes it for nectar becomes stuck in it.
