Mexican Pinguicula make excellent house plants and are among the easiest carnivorous plants to grow. In the wild, many Mexican Pinguicula grow in seasonal fog forests on limestone cliffs and tree trunks. Some grow in moss, others just cracks in the rocks, quite often on north facing cliffs. To understand more about the lives of Mexican Pinguicula please see the travelogues at World of Pinguicula.
Most of the Mexican species have heterophyllous leaves—the summer leaves are slimy and carnivorous; the winter leaves are succulent and not carnivorous. The plants like warm humid conditions when in the summer, carnivorous state. During the winter when they are in the succulent state they should be kept cooler and drier. Since these conditions are typical of those in a house they make great house plants in a bright sunny window. If you can grow African violets you can grow most Mexican Pinguicula.
There is some controversy over the best way to grow Mexican Pinguicula. Techniques that some growers swear by are death in other hands. Mexican Pinguicula are NOT bog plants and should not be grown like bog plants. Plants in the standard peat and sand "CP mix" may or may not do well depending on your exact conditions and which species or hybrid you have.
Most Mexican Pinguicula prefer an alkaline soil mix. I find a good mix for house plant pings to be one part each of peat, coarse sand, and perlite. Dolomitic or limestone sand would be best if you can get it. This would counteract the acidity of the peat. I use silica sand blasting sand in the mix because that is what I can get. I then add dolomitic lime (a soil amendment found in garden shops) to the mix. I put in about 1 tablespoon of dolomitic lime per cup of soil mix. That may seem like a lot but the plants do much better with it there.
There are other options on soil mixes that do work as well. You can use pumice in place of the perlite. Some growers may use vermiculite but it breaks down quickly getting slimy and requiring you to repot often. You can throw in some fine orchid bark but it will degrade in a year or two. Ground bark might actually be better and a good substitute for peat since it would be less acidic. A problem with bark products is many that are sold for orchids have added fertilizer. However, a number of growers have reported success using standard, peat-based potting soil with extra perlite. The potting soil comes already pH adjusted which makes it easy to use.
The main issue with soil mixes is matching the weight or water holding ability of the soil to the temperature and humidity where the plants are growing. Plants grown in humid greenhouses with misty or overhead watering need to be in a light or more loose soil mix. Plants grown in a typical house or classroom need a heaver, water absorbent mix. I never top water my plants and the pots are always sitting in a few cm of water. That is the reason I recommend a heaver mix than many growers at World of Pinguicula.
After planting the plants I then put a layer of silica sand on the surface of the soil up to 5 mm thick to discourage fungus gnats. Fungus gnat larvae like to eat Pinguicula leaves. I plant all my Pinguicula in 9 cm tall plastic pots and grow them using the classic tray method. When the plants have carnivorous leaves I use a water depth of up to 4 cm in the trays. When the plants are in the succulent phase I keep the water level lower but never dry. Many of the hybrids bloom constantly. After about five years they need repotting because the deep thatch of old leaves get in the way of the new roots reaching the soil from the growing plants.
Most if not all Mexican Pinguicula can not self pollinate their flowers for physical reasons. The stigma forms a flap over the anthers. The outward facing part of the stigma is the part receptive to pollen. The inward facing non-receptive part covers the anthers keeping the pollen from getting to the receptive part of the stigma without mechanical assistance from a pollinator, usually a hummingbird.
Because of the way the flowers are constructed, it is tricky to pollinate them by hand. The easiest way to pollinate the flowers is with a tooth pick. You could play hummingbird tongue by poking the toothpick in and out of the flower trying to pick up the pollen from the anthers on the way out and deposit it on the stigma on the way in. However a more reliable way is to rip the flowers to get at the anthers and stigmas directly. To rip the flowers hold the top petals with one hand and the lower petals with the other and carefully tear off the lower petals. Do not touch the stem as you are likely to damage it. You can use a toothpick to transfer pollen the from the anthers to the stigma or use a forceps to remove the stamens and paint the stigma with the anthers. It may take some practice.
For good germination the seeds need temperatures between 15°C and 25°C (60°F to 80°F). To prepare a pot to start your seeds, fill it most of the way to the top with your favorite mix with the top cm being a sifted part of your mix so it is finer. Place the seed on the surface of the medium and don't bury it. The soil should be damp and not sopping wet. You may want to put the pot in a plastic bag if your environment is dry. You get better control germinating seeds under lights although in the shade of a greenhouse works. Seeds germinate in 4 to 8 weeks. Please see Sowing Seeds Step-by-Step for more details on starting seeds.
Do NOT ever use any kind of fungicide or pesticide on Pinguicula. This includes all Pinguicula species. I don't know why but fungicides especially are death even in the soil. This even includes cinnamon which can be used as a fungicide on other plants. Insecticides on the soil around mature plants appear to be OK.
Heterophyllous species of Mexican Pinguicula need seasonal light cues to be maintained long term. With proper light cues most species will have carnivorous leaves from mid spring through fall. Winter through early spring they will have succulent, non-carnivorous leaves. Heterophyllous species grown under continuous light period will essentially get stuck in the non-carnivorous phase. Homophyllous species such as Pinguicula gigantea do tolerate a continuous light period.
The seasonal changes are cued by light, not moisture. Water the plants according to the leaf type, not season. When the plants have carnivorous leaves they need to be kept moist and enjoy high humidity although they do just fine at 20% relative humidity. When they have succulent leaves the plants need less water. Keep the soil lightly damp. Some species can be totally dry if the air is very humid. Chances are your conditions are not humid enough so don't let the plants dry out.
Mexican Pinguicula can be propagated by carefully removing succulent leaves. The best time is just before new carnivorous leaves appear in the late winter or early spring. Please see Mexican Pinguicula Leaf Pullings for instructions. The transition time between succulent and carnivorous leaves is also the best time to repot Mexican Pinguicula.
-- John Brittnacher
For more information please see:
Powell, Charles L. (1987) Mexican Pings. Carniv. Pl. Newslett. 16(4):106-110 ( PDF )
Beckstrom, Marc (1979) A Search for Mexican Pinguiculas. Carniv. Pl. Newslett. 8(2):55-57 ( PDF )
Lau, Alfred B. (1993) The discovery of a new Pinguicula from Ayautla, Oaxaca, Mexico. Carniv. Pl. Newslett. 22(1-2):26-27 ( PDF )
Wix, Lloyd (1998) Pinguicula emarginata -- a variable and distinctive Mexican species. Carniv. Pl. Newslett. 27(4):121-123 ( PDF )
Pinguicula moctezumae sprouts. Note the cotyledons have glands! This may be common among Pinguicula but most other CP genera have cotyledons totally unlike their regular leaves. The red arrows point to something else not expected. They have a stem-like tap root with root hairs. While the presence of a tap root is the norm among plants, in Pinguicula, a tap root is only seen in newly sprouted seedlings. In the upper sprout you can see a typical Pinguicula adventitious root extending from the base of the first leaf formed.
Here is a Pinguicula moctezumae seedling a few weeks later. The red arrow points to the degenerating tap root/stem. The plant is squatting down into the usual Pinguicula position. Note the adventitious roots coming out of the bases of the leaves.
Pinguicula cyclosecta flowers. These plants are growing next to a window and are greener than plants grown in a greenhouse.
Pinguicula cyclosecta in the fall. The leaves are carnivorous and have drool edges. The upturned leaf edges keep the digestive juices from flowing off the edge of the leaves.
Here is the same Pinguicula cyclosecta plant in the spring at about the same scale. It has small, succulent, non-carnivorous leaves.
In Pinguicula flowers the stigma forms a flap over the anthers. The receptive side of the stigma is the outer part so the flower will not self pollinate. This flower is "opened" to see the details.
The flowers are usually pollinated by humming birds. As a bird sticks its tongue into the flower any pollen on the tongue is deposited on the receptive part of the stigma. As the bird removes its tongue it collects pollen off the anthers without getting any (or much) on the top of the stigma.
A forceps is holding up the stigma to see the anthers at the top of the C-shaped stamens.
Pinguicula ehlersiae flower.
P. ehlersiae plants are a few cm wide and quite cute.
Pinguicula 'Pirouette' is a complex hybrid: Pinguicula agnata x (moranensis x ehlersiae). Most Mexican Pinguicula species can be hybridized.
Pinguicula moctezumae is easy to propagate from seed. But you need to pollinate the flowers by hand or let hummingbirds do it for you.
Pinguicula gigantea makes a great window sill plant. This species does not form succulent leaves in the winter but the plants do get smaller. They bloom in early winter.