Butterwort care differs depending on the origin of the plant. Most simply, they can be divided into temperate, warm temperate, and tropical/Mexican varieties, although some plants may have more nuanced care. Perhaps the most common butterwort found in cultivation, including sometimes at hardware stores, is the warm temperate Pinguicula primuliflora.
Where to Grow: Temperate species can be grown outdoors, while warm temperate and tropical varieties should be grown indoors.
Light: Most butterworts should be given partly sunny conditions if outdoors (temperate varieties) or very bright artificial light indoors.
Water: Use distilled/rainwater/reverse osmosis water ONLY. That means NO TAP WATER. Keep the plants in a tray with about an inch of water at all times. For Mexican butterworts, keep the soil only slightly damp over the winter, when the plants shed their carnivorous leaves and adopt succulent leaves instead.
Soil: Use a 50:50 mix of sphagnum peat moss and coarse (#12 silica sand or similar) sand. If sand cannot be found, perlite can also be substituted. Make sure all soil ingredients are free of fertilizers and added minerals. While the soil mixture can be similar to that of other carnivores, like flytraps and North American pitcher plants, butterworts tend to prefer airier mixtures - adding a bit of perlite or pumice can help to achieve this.
Containers: Plastic pots are best. Avoid unglazed terra cotta plants, because they can wick water away from the plants and also leach minerals into the soil. There is no need for a very deep pot because butterworts have very short roots. Many growers have grown them on large pieces of lava rock or in shells.
Feeding: The plants will likely catch all the insects they need, but can also be fed very small insects like ants or fruit flies.
Fertilizing: As a general rule, avoid using any fertilizer on butterworts.
Humidity: Usually not a concern.
Dormancy (Winter Care): Temperate sundews will go into dormancy in the winter months, generally between October and March. During this time, they will produce a hibernaculum, which resembles a rosette of tightly packed, short leaves. Dormancy is triggered by shorter daylight hours and colder temperatures. In the mid-Atlantic region, plants can overwinter outdoors provided they are either mulched heavily with pine needles/bark (bury the pots under several inches of mulch) or placed into a cold frame. Alternatively, some growers have had success with placing the plants in an unheated garage as long as the plants can still receive some light. During dormancy, the soil should be kept damp, not very wet. The plants can survive frosts and even some brief freezes. Mexican butterworts do not undergo a true dormancy in the winter, but lose their carnivorous leaves and resemble succulents. During this period, reduce the amount of water and keep the soil only slightly damp.