Butterworts

What they are

Butterworts are small plants, most of them a flat rosette of leaves 5 to 10 cm (2 to 4 in) across pressed to the ground, with short roots and a single flower on each tall stalk. The whole leaf surface is the trap. It is covered in tiny stalked glands, each holding a droplet of sticky mucilage, which gives the leaf a greasy sheen. A gnat or springtail that lands is held by the glue; glands on the leaf then release digestive fluid and take up what dissolves, and around a larger catch the leaf edge rolls slightly inward. A butterwort is flypaper with a digestive system, and its prey is small: fungus gnats, fruit flies and springtails.

The flowers are the other reason to grow them: violet-like, spurred and two-lipped, in purple, violet, pink, white or yellow, and Mexican species carry them for months. Nearly all butterworts need a pollinator or a hand to set seed, so a windowsill plant does not sow itself around.

The family is the Lentibulariaceae, shared with the bladderworts and the corkscrew plants; butterworts are its earliest branch and have its simplest trap. Current treatments recognise about 100 species, more than 40 of them in Mexico and most of those found nowhere else.

Where they grow

The range runs across Europe, northern Asia and North America, through Mexico and the Caribbean to the Andes, with outliers in Morocco and the far south of South America. The sites share wet, nutrient-poor ground: bogs, fens, stream sides, seepages and dripping rock. Unlike most carnivorous plants, many grow on alkaline ground: European species on limestone and tufa, Mexican species on limestone cliffs and mossy trunks in seasonal fog forest, often on north-facing rock with little direct sun.

Climate explains the three groups a grower deals with. Northern species live where the ground freezes and survive winter as a tight bud. Mexican species live where winter is dry rather than cold and survive it as a compact rosette of succulent, non-sticky leaves. The species of the southeastern United States and the Caribbean live where winter is mild and wet and keep their carnivorous leaves all year.

The range in cultivation

Mexican and other tropical species are the butterworts a beginner meets. Pinguicula moranensis, P. agnata, P. esseriana, P. ehlersiae, P. gigantea and hybrids such as ‘Weser’ and ‘Sethos’ make up almost everything sold in shops. They grow at room temperature, need no cold, most switch each winter to a small succulent rosette that must be kept nearly dry, and they tolerate mineral-based, slightly alkaline mixes and an ordinary bright windowsill; anyone who can grow African violets can grow most of them.

Temperate species such as P. vulgaris, P. grandiflora and P. alpina belong in an outdoor bog garden, a cold frame or an unheated greenhouse in a climate with real winters. They shrink to a winter bud, called a hibernaculum, and they need cold winter temperatures to survive. They are not houseplants. P. grandiflora, native to Britain and Ireland and fully hardy (H6), is the one to try first.

Warm-temperate species of the southeastern US coastal plain, P. caerulea, P. lutea, P. primuliflora, P. planifolia, P. pumila and the rare P. ionantha, with the tiny European P. lusitanica, keep their leaves through a mild winter in permanently wet, acid peat. They are short-lived perennials, or an annual in P. lusitanica, that flower themselves to death unless seed is saved. They are harder than the pitcher plants and sundews they grow beside, with P. caerulea the easiest. They take a light frost but not a hard freeze.

Molecular work separates the three groups along roughly these lines, and new Mexican species keep being described, so a plant’s behaviour is a better guide than its label.

Growing them

Light

Bright light with some direct sun, and flowering depends on it. Mexican species blush pink or copper in strong light but scorch in a hot afternoon window, so a bright east window or a grow light is ideal, and in a greenhouse they want more shade than most carnivorous plants. Temperate species want sun on the leaves and cool roots. Under artificial light, give Mexican species a day length that changes with the seasons; a plant on a fixed timer can get stuck in one leaf type.

Water

Rain, distilled or reverse-osmosis water. Temperate and warm-temperate species are kept permanently wet in a tray; the warm-temperate species also do well in undrained containers. Mexican species are the exception. In summer growth keep up to 2 cm (0.8 in) of water in the tray; once the succulent rosette forms, let the tray dry for about a week or more between waterings. The rule is that the smaller the winter leaves, the drier the winter must be. For temperate species the danger runs the other way in both seasons: a hibernaculum kept wet rots, and a plant that dries out in summer is lost.

Growing medium

Mexican species take a mostly mineral mix. One mix is equal parts peat, coarse sand and perlite with about a tablespoon of dolomitic lime per cup of mix; another is equal parts sand, perlite and pumice or lava rock with one part peat and no lime. Both are open and fast-draining with only a quarter to a third peat, which is the point. Warm-temperate species want three parts peat to one each of sand and perlite, or pure peat. Temperate species take two parts peat to one each of sand, perlite and vermiculite, or for the lime-loving P. alpina equal parts limestone grit and peat. Pots can be shallow.

Temperature

Mexican species are comfortable at room temperature, roughly 15 to 30 °C (59 to 86 °F); most are mountain plants that take cool summer nights. They are not frost hardy. Keep them above 5 °C (41 °F) in winter; a winter night minimum of around 8 °C (46 °F) is the usual recommendation for the group. Temperate species need a frozen or near-frozen winter and cool summers. Warm-temperate species survive light frost only.

Dormancy

Each group rests differently, and the wrong rest is the commonest way to lose a butterwort. Mexican species make a succulent rosette through winter; it is not a true dormancy, since the plant stays green and often flowers, but it must be kept nearly dry and in good light. Temperate species form a hibernaculum in early autumn and are then kept cold and barely damp until spring; the bud of P. alpina keeps its roots, so move it with care. Many temperate species also produce gemmae, small brood buds around the hibernaculum, which are the easy way to multiply them. Warm-temperate species have no resting stage.

Feeding

None is needed; a butterwort among houseplants clears fungus gnats on its own. Some growers give Mexican species a light fertilisation of the medium; root-zone feeding can do damage, and a very dilute foliar spray, kept off the flowers, is the safer choice. Outdoor temperate and warm-temperate plants get nothing at all.

Common mistakes

Treating the genus as one plant: a Mexican butterwort watered through winter rots, a temperate one brought indoors dies for lack of cold.

Spraying for mould. Fungus appears in dim, stagnant, humid winters; change the conditions, and do not use any fungicide on butterworts, cinnamon included. Pesticides can also harm them.

Expecting seed. Nearly all species need hand pollination, and the Mexican species cannot pollinate themselves; see the propagation entry.

Buying by name. Mexican species cross readily in cultivation, and much of what is sold as a species is a hybrid or an unlabelled clone.

Which to start with

Pinguicula moranensis is the obvious first butterwort: large, generous with flowers, tolerant of a windowsill and easy to rest. The hybrids ‘Weser’ and ‘Sethos’ behave the same way and are frequently the plant actually in the pot. P. esseriana is a good second, a miniature whose winter leaves detach and root into new plants by themselves; P. agnata and P. gigantea are the windowsill picks among species that skip the winter rosette.

Leave the temperate species until you have somewhere cold to keep them, and the southeastern US species until you are willing to sow every year.

Going further

The Mexican group leads to rarer species and hybrids with the same care: P. laueana, grown for its red flowers, and P. gypsicola and the bulb-forming P. heterophylla and P. macrophylla for growers who can keep a bone-dry winter. Leaf pullings make the Mexican species the easiest carnivorous plants to multiply, and gemmae do the same for temperate species; both are in the propagation entry. The water and media and light guides cover the shared basics.