Biological gnat control — Pinguicula gigantea

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Pinguicula gigantea, giant butterwort.  At upper left, a cluster of smaller Mexican butterworts are producing their winter rosettes while retaining a few larger summer leaves.

Butterworts, genus Pinguicula, are carnivorous plants that trap and digest small insects with slimy secretions produced by glands covering the surface of their leaves.  The plants are capable of absorbing nitrogen from the digested prey, allowing them to grow under nutrient-poor conditions such as peat bogs or, as in the case of the species illustrated above, seasonally wet seeps on exposed, bare rock (habitat photos here).

The Pinguicula species native to North Carolina are relatively small plants with leaf rosettes only a couple of inches across, but P. gigantea can grow to the size of a large dinner plate.  Its native habitat is in the Mexican state of Oaxaca, but the plants adapt well to cultivation.  They’re particularly useful for controlling the fungus gnats that can infest the soil of potted house plants, and in my greenhouse they have also trapped flies and small cockroaches.

Ping_gigantea leaf
fungus gnats trapped on P. gigantea leaves

In addition to their usefulness as pest control, P. gigantea plants also produce lovely flowers, pale purple with a darker edge to each petal.

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Mexico is home to many beautiful species of butterworts which can be quite tricky to grow.  Most of the species require a definite dry dormancy, during which they produce smaller, more succulent non-carnivorous leaves in a tighter rosette (see the smaller plants in upper left of the first photograph, above).  If watered too much (or at all) while dormant, they are likely to rot.  During the summer, they like to remain moist, but many of the rock-growing species require an inorganic mix and will rot if grown a soil- or peat-based mix.  I have grown many Mexican Pinguicula species at various times, but P. gigantea is one of only a few species that I have been able to maintain for more than a couple of years.

P. gigantea does have a winter dormancy, but it is less extreme than some of the other species.  Leaf size decreases only slightly, and the plants are tolerant of year-round moisture.  Instead of a mineral-based mix, I grow my P. gigantea in pure long-fiber sphagnum moss.  Or, more accurately, I grow them on sphagnum.  The thin, rather feeble-looking white roots spread across the surface of the moss and among the mat of dead leaves that slowly builds up, rather than penetrating deeply into the pot.

Propagation of this and other butterwort species is easy.  The somewhat brittle leaves detach easily from the rosette, and if placed on moist sphagnum, perhaps in a plastic bag to keep humidity high, will reliably produce a few plantlets at the broken base of the leaf.

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5 thoughts on “Biological gnat control — Pinguicula gigantea

  1. Nick,
    Using Pinguicula is certainly an interesting and beautiful means for fungus gnat control. I love the flowers, but have always found the rather sickly looking green leaves a bit off-putting. Still the plant does have its merits. I’ll try Pinguicula gigantea if I can find a local source.

    Minus the Pinguicula, I control fungus gnats successfully in potted plants by adding “Mosquito Bits” (Bacillus thuringiensis ssp. israelensis) to the water in the watering can, let it steep a short while, and water away. It’s not immediate control, but it does work for me. If I stop using it for a length of time, the gnats return.

    Yellow sticky traps laid horizontally are another control, but not nearly as effective for me as the Mosquito Bits. (No, I don’t own stock in Mosquito Bits.😉)

    Thanks for your blog.

    Liked by 2 people

    1. Hi Mike, Thanks for the suggestion. I have used a B. thurigensiis product (can’t remember if it was Mosquito bits) in the water trays holding bog plants, but I never thought of applying it directly to the soil of potted plants. That’s a great idea for seedlings and plants that can’t tolerate dry soil.

      Like

  2. Thank you for this solution. I have a Drosera Capensis but it must have had indigestion … so I use yellow stickers and they do the job. Your carnivorous plant seems very interesting … what is its minimum temperature in winter?

    Liked by 1 person

    1. I keep my greenhouse at a minimum of 15.5 C, because I keep some lowland tropical species. I don’t know how low P. gigantea would go—probably not very cold, because it is from low altitude in Oaxaca. Some of the other Mexican pinguicula might be more cold tolerant.

      Liked by 1 person

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