Carnivorous plants pique the interest of every gardener and houseplant hoarder at some point, but bringing a Venus flytrap home on a whim with no idea how to care for it will soon lead to disappointment. Fortunately, to explain how to keep carnivorous plants alive and thriving, my guest this week is International Carnivorous Plant Society Education Director Kenny Coogan, who runs a successful carnivorous plant nursery.
Kenny has a master’s degree in global sustainability, and his professional experience with carnivorous plants started 15 years ago when he co-founded the Western New York Carnivorous Plant Club. Since then, he moved to Tampa, Florida, to teach middle school science and agriculture and was awarded Best Beginning Science Teacher statewide, and now he is in the carnivorous plant nursery business full time. He’s also a writer with more than 400 bylines on pets, livestock and gardening for Countryside, Hobby Farms, Chickens, Backyard Poultry, and Florida Gardening magazines, among other publications.
This summer, Kenny will publish his book “Florida’s Carnivorous Plants: Understanding, Identifying, and Cultivating the State’s Native Species,” which is designed for hobbyists and budding naturalists. The book includes identification and growing guides plus the history behind the discovery of these plants. (joegardener Show listeners can order at Rowman.com and enter FLCP30 for 30% off through August 1, 2022.)
Having read an advance copy of Kenny’s book, I have developed a new passion for carnivorous plants. Growing up in Miami, I fell in love with the Venus flytrap and some others but never really got deep into it. Now I am so fascinated by how these plants work. Fortunately, Kenny is a wealth of knowledge about carnivorous plants.
Kenny leads the book with an appropriate quote from Charles Darwin: “The fact that a plant should secrete, when properly excited, a fluid containing an acid and ferment, closely analogous to the digestive fluid of an animal, was certainly a remarkable discovery.”
How cool is it that a plant digests its prey just as an animal digests its prey?
Asked to name a carnivorous plant, most people will say Venus flytrap (Dionaea muscipula). Kenny wants you to know that there is incredible diversity among this group of plants. Even experienced gardeners are surprised to learn there are 999 more species of carnivorous plants. Their prey ranges in size from microscopic organisms to mice, rats and birds.
Carnivorous plants grow all over the world. In North America, they are found mostly in boggy conditions, in which the soil is saturated year-round. Canada has the purple pitcher plant (Sarracenia purpurea), and the United States has carnivorous plants over a wide range, with most found in the Southeast and a couple of unique ones found in California.
Florida has the most carnivorous plant species in the United States, numbering a little more than 30, and half of those are bladderworts, which are very minute plants, Kenny says.
How Kenny Coogan Came to Love Carnivorous Plants
Kenny had a lot of livestock while growing up — pigeons, ducks, geese and chickens — but then his parents said “no more.” However, they would allow him to have a Venus flytrap, the closest thing to an animal that he was permitted to have.
Kenny had that first Venus flytrap for about a month, which is the average lifespan for Venus flytraps that are in the possession of people who don’t know how to care for them. (Well-cared-for flytraps can live 15 to 20 years.)
A couple of years later, when Kenny was in high school, the school hall monitor, Bruce Herman, gave a guest lecture on carnivorous plants. The hall monitor brought a collection of 15 plants to show the students. Kenny learned that there was more to carnivorous plants than just Venus flytraps, and he wanted to learn everything there was to know about them. Of the 220 kids that Bruce presented to that day, Kenny was the only student who showed a real interest, so Bruce gave Kenny a sundew from South Africa and a Venus flytrap. “Despite Mr. Bruce Herman doing a wonderful presentation, I also killed them probably four or six weeks later,” Kenny recalls.
At college, Kenny found others who were interested in carnivorous plants, and he knew Bruce would be a great resource for them. Kenny has now been growing carnivorous plants for about 17 years — with much higher success rates than his early efforts.
How Carnivorous Plants Are Defined
Carnivorous plants, in general, have three traits:
Lures: They attract prey using color or scent. The color or scent is produced by modified leaves, but not flowers. No carnivorous plants use flowers to attract prey.
Traps: Trapping mechanisms include the snap shut (example: Venus flytraps, Aldrovanda) the pitfall trap (ex: various pitcher plants), the sticky trap (ex: Byblis, Drosera Drosophyllum, Pinguicula, Roridula), the suction cup trap (ex: bladderworts), and lobster pot traps (Genlisea, Darlingtonia and Sarracenia psittacina).
Digestion: They absorb the nutrients from their prey either using their own enzymes, symbiotic insects or beneficial bacteria.
There are other plants that trap prey but don’t digest it, such as thorned plants, sticky flowers and thistles. Though those plants can kill insects, they only kill defensively, not offensively.
Historically there is a 60-kilometer radius around Wilmington, North Carolina, where Venus flytraps are found naturally, though the population has dwindled due to poaching. In the 1970s and ’80s, a few people started sowing Venus flytrap seeds in the panhandle of Florida, and they have since naturalized there. (Likewise, there is an invasive population of North American pitcher plants in Europe.)
There are dozens of cultivars of Venus flytraps registered in the last 30 years that are larger, more brilliant and more colorful than wild ones. According to Kenny, the cultivars are often propagated through tissue culture quite cheaply, so it doesn’t make sense for anyone to poach wild Venus flytraps anymore.
A single Venus flytrap can have six to 30 traps, or snapping lobes, at a time, Kenny says. Each lobe can open and close and digest three or four times before it is spent. New traps grow from the center of the plant during the growing season.
Each trap has two lobes, and each lobe has two to four trigger hairs. If the same trigger hair is touched twice within 20 or 30 seconds, it will send a chemical signal to the lobe on the opposite side. Water will move from the outside of the lobe to its side, and that causes the trap to snap shut. The more the prey struggles, the tighter the seal on the trap gets. It takes four to 10 days for the plant to digest its meal, leaving only an exoskeleton.
If you have a healthy Venus flytrap, you can play with it, Kenny says. Using a finger or stick, you can cause a trap to snap shut. If the trap closes slowly, it probably means the plant doesn’t have enough light, he notes.
Don’t play with a Venus flytrap too much or it will expend its energy and use up its traps while gaining none of the nutrition it needs to grow new traps.
North American pitcher plants (Sarracenia) have a range that starts halfway up Canada and goes down the East Coast to Central Florida. There are several different species and several naturally occurring hybrids. Some species or hybrids have pitchers that are only a couple of inches long while the biggest pitchers are nearly 3 feet long.
The largest pitcher plant is Nepenthes rajah, which is native to Southeast Asia. It can hold more than a liter of water. Breeders cross Nepenthes rajah with other pitcher plants to develop larger and larger commercially available pitcher plants.
Each pitcher has four to five zones that each serve a different purpose. The top zone, the lid, is a landing pad for insects. Some lids have nectar on top and some have nectar on the underside. Scientists have recently discovered that the nectar contains a chemical that gets the bugs a little drunk so they fall down into the pitcher, Kenny says. He adds that most of the North American species use their lids to keep rainwater out but a species found in Florida (and one in Canada) has an upright lid to welcome rainwater. The Florida species uses bacteria to break down prey while the other species use enzymes.
The second zone is slippery, so much so that a Harvard researcher replicated the composition of a tropical pitcher plant to create a frictionless surface for self-cleaning windows and oil and blood transfusions. Hairs pointing downward prevent insects from climbing back up and out of the pitcher.
The bottom zone is where the digestive enzymes are.
Kenny sometimes notices spiders and frogs hanging out on the “lips” of his Sarracenia plants. The spiders and frogs go spelunking into the pitchers to steal food, and they make it back out without becoming prey themselves.
Sundews are found on every continent except Antarctica. They work like flypaper: Insects land on sticky leaves and can’t escape. Once an insect is detected, the plant produces an enzyme to digest its prey right where it landed. Some sundew species, like the South African D. capensis, curl their leaves around bugs that land on them to aid in digestion.
The sticky substance on sundew leaves is one of the strongest adhesives found in nature.
There are more than 200 known species of bladderworts (Utricularia). They can be aquatic, terrestrial or epiphytic. They are so-named because they have little bladders that look like roots but are actually modified leaves. When protozoa and other microscopic organisms go by, bladderworts set a trigger and in a millisecond a little pouch sucks them in. The pouch then expels anything extra it sucked up, like water, and then fills with digestive enzymes.
Bladderwort pouches range from the size of the period at the end of the sentence to the size of a BB.
One of Kenny’s favorite carnivorous plants is Aldrovanda vesiculosa, the waterwheel plant. It is fully aquatic and the only other extant species that has snap traps like a Venus flytrap. Kenny struggled to grow Aldrovanda vesiculosa for five years but now he knows the trick to success: They like to grow with other plants. They need some carbon dioxide in the water, so he grows them with water chestnuts, Vietnamese coriander and other aquatic plants.
Though other growers can raise Aldrovanda vesiculosa in shallow greenhouse trays, Kenny finds he needs a container that holds at least 15 gallons of water to grow a 6-inch Aldrovanda vesiculosa. The large volume of water protects the plants from rapid temperature changes.
Selling Plants in a Pandemic
“At the start of the pandemic, people were really going plant crazy,” Kenny says.
He saw a big uptick in business as people who were stuck at home clamored for a living thing to share their workspace. He shipped plants, packaged in coolers with heat packs, all over the country.
Propagating Carnivorous Plants
To make more carnivorous plants, Kenny propagates from seed or through vegetative propagation. Which method he uses depends on the genus of the plant he is propagating.
Sundews (Drosera) are tiny, sticky and delicate plants that can be easily propagated by chopping a plant up, Kenny says, though they also are prolific seeders. They flower multiple times a year, and one plant can yield 40 to 50 plants from seed in a couple of months. Kenny doesn’t sell seeds, but when someone buys one of his sundews he shares a care sheet that explains how to collect the seeds and sow them.
When Venus flytraps are dormant in fall and winter, their rhizomes can be separated to make more plants.
The Best Growing Medium for Carnivorous Plants
North American carnivorous plants do well when grown in a mix of half peat and half perlite.
Mexican butterworts (Pinguicula) do better with a more airy aggregate that is heavier on the perlite. Tropical pitcher plants like 100% long-fiber Sphagnum moss, or a combination of Sphagnum and perlite.
Kenny doesn’t like using peat because it is not environmentally sustainable. Like me, he is experimenting with PittMoss, a peat alternative that is made from recycled paper. In November, he took 18 Venus flytraps and planted six in 100% PittMoss, six in half PittMoss, half perlite and six in PittMoss with a little sand. He is monitoring the plants’ growth and also using his water meter to test if the PittMoss is leaching anything. To date, the Venus flytraps in 100% PittMoss are keeping up with the other plants.
The Best Pots for Carnivorous Plants
Because most carnivorous plants won’t tolerate lots of minerals, they should not be grown in terracotta, which can leach minerals. Glazed pots or plastic pots are best.
Maggie Chen (and now Kenny) uses 7-to-9-inch-tall white pots for her Venus flytraps. Big pots allow the plants to grow big roots, and big roots support big top growth. The white color reflects the sun so the roots don’t bake. The pots sit in a tray that is kept full with half an inch of water so the substrate stays moist at all times.
Venus flytraps that are grown indoors need a grow lamp for 12 to 16 hours a day. Outdoors, they can handle the cold down to the upper 20s. Place them in full sun so they can reach their full size and come into their color. When they die back in winter, don’t throw them away; they will return in spring.
Most North American pitcher plants, tropical pitcher plants and sundews are fine in a 3-to-6-inch plastic pot for the first few years, Kenny says. Tropical pitcher plants can grow to have a 9-to-15-foot vine but still only need 1-to-3-gallon pots because they get their nutrients from their prey rather than from the soil.
Watering Carnivorous Plants
Carnivorous plants need more water than your typical houseplant. Common plants like Venus flytraps, many North American and South African sundews and North American pitcher plants do great when they sit in an eighth or quarter-inch of water all the time.
Most carnivorous plants require pure water. To ensure a water source will be safe for his plants, Kenny uses an inexpensive water meter that reads how many parts per million of total dissolved solids are in the water. Pure water has 0 ppm, while EPA-approved tap water can have up to 500 ppm.
Tap water can be filtered using a reverse osmosis system to get under the 50 ppm mark that most carnivorous plants require. If you have only a couple of plants, Kenny recommends buying distilled water — but not spring water, which contains minerals.
To water his 1,500 plants, Kenny collects rainwater off his metal roof in six 50-gallon rain barrels. The rainwater is free of the salts and minerals found in his tap water, which has 400 ppm of total dissolved solids. When he tests the rainwater, it ranges from 0 to 20 ppm.
If you use water that is less than pure, you’ll want to repot your carnivorous plants annually to prevent mineral build-up. Maggie Chen, an award-winning grower, shared last year on World Carnivorous Plant Day that she was able to grow Venus flytraps with 2-inch traps (compared to ¾-inch traps on wild flytraps) because she changes the plants’ substrate two times a year.
Fertilizing Carnivorous Plants
Conventional houseplant food has more nutrients than a carnivorous plant can handle. The International Carnivorous Plant Society recommends simply feeding your carnivorous plants bugs, but if you do want to give the plants an extra boost, you can use seaweed-based fertilizer like Maxsea, Kenny says. Maxsea has a 16-16-16 nutrient ratio, and he recommends using it at quarter strength.
Providing Light to Carnivorous Plants
Many carnivorous plants need full sun because their traps are not as good at photosynthesizing as other plants.
Many Florida species thrive in areas where naturally occurring wildfires are frequent because they don’t have to compete with an overstory. Wild-fire suppression is causing shrubs and trees to outgrow native carnivorous plants.
What to Do When You Get a Carnivorous Plant Home
There are not many carnivorous plant nurseries, so chances are you’ll find the plants you want online, Kenny says. If a plant arrives bare-root, pot it. If it comes potted, water it really well. The plant will need to be hardened off before it can go outdoors. Introduce it to the sun gradually, over the course of a week, instead of just putting it out for a full day immediately, which can burn the plant.
Plants from a good online vendor will have new growth and good soil. The soil should not appear as if the plant was just dug up. Kenny knows of several nurseries — located in Thailand, Sri Lanka and Australia — that sell tropical pitcher plants with serial numbers. The serial numbers reveal the plants’ heritage so you can learn what wild-harvested plants were crossed long ago to produce the hybrid. The hybrids are all raised via tissue culture so they are sustainable.
If you find a carnivorous plant locally, chances are it’s at a big-box store. The plants there tend to come in little plastic cubes that a lot of people refer to as “death cubes,” Kenny says. That’s because those big-box stores — if they are watering the plants at all — are not using pure water. Plus, those cubes act as a mini-greenhouse, bombarding the plants with heat.
Kenny’s No. 1 choice is to buy plants at a local plant show, where the seller likely has the same growing conditions as you do.
The 2nd annual World Carnivorous Plant Day is May 4, 2022, sponsored by the International Carnivorous Plant Society. Knowing what you just learned, maybe you’ll celebrate by adding something carnivorous to your plant collection.
I hope you enjoyed my conversation with Kenny Coogan and learned something new about carnivorous plants. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.
Have you had success raising carnivorous plants? Let us know in the comments below.
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“Florida’s Carnivorous Plants: Understanding, Identifying, and Cultivating the State’s Native Species” by Kenny Coogan – Order at Rowman.com and enter FLCP30 for 30% off your order! Offer valid through August 1, 2022.
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