Carnivorous Plant - Cultivation

Cultivation

Although different species of carnivorous plants have different requirements in terms of sunlight, humidity, soil moisture, etc., there are commonalities.

Most carnivorous plants require rainwater, or water that has been distilled, deionised by reverse osmosis, or acidified to around pH 6.5 using sulfuric acid.

Common tap or drinking water contains minerals (particularly calcium salts) that will quickly build up and kill the plant. This is because most carnivorous plants have evolved in nutrient-poor, acidic soils and are consequently extreme calcifuges. They are therefore very sensitive to excessive soil-borne nutrients. Since most of these plants are found in bogs, almost all are very intolerant of drying. There are exceptions: tuberous sundews require a dry (summer) dormancy period, and Drosophyllum requires much drier conditions than most.

Outdoor-grown carnivorous plants generally catch more than enough insects to keep themselves properly fed. Insects may be fed to the plants by hand to supplement their diet; however, carnivorous plants are generally unable to digest large non-insect food items; bits of hamburger, for example, will simply rot, and this may cause the trap, or even the whole plant, to die.

A carnivorous plant that catches no insects at all will rarely die, although its growth may be impaired. In general, these plants are best left to their own devices: after underwatering with tap-water, the most common cause of Venus flytrap death is prodding the traps to watch them close and feeding them inappropriate items.

Most carnivorous plants require bright light, and most will look better under such conditions, as this encourages them to synthesise red and purple anthocyanin pigments. Nepenthes and Pinguicula will do better out of full sun, but most other species are happy in direct sunlight.

Carnivores mostly live in bogs, and those that do not are generally tropical. Hence, most require high humidity. On a small scale, this can be achieved by placing the plant in a wide saucer containing pebbles that are kept permanently wet. Small Nepenthes species grow well in large terraria.

Many carnivores are native to cold temperate regions and can be grown outside in a bog garden year-round. Most Sarracenia can tolerate temperatures well below freezing, despite most species being native to the southeastern United States. Species of Drosera and Pinguicula also tolerate subfreezing temperatures. Nepenthes species, which are tropical, require temperatures from 20 to 30 °C to thrive.

Carnivorous plants require appropriate nutrient-poor soil. Most appreciate a 3:1 mixture of Sphagnum peat to sharp horticultural sand (coir is an acceptable, and more ecofriendly substitute for peat). Nepenthes will grow in orchid compost or in pure Sphagnum moss.

Ironically, carnivorous plants are themselves susceptible to infestation by parasites such as aphids or mealybugs. Although small infestations can be removed by hand, larger infestations necessitate use of an insecticide.

Isopropyl alcohol (rubbing alcohol) is effective as a topical insecticide, particularly on scale insects. Diazinon is an excellent systemic insecticide that is tolerated by most carnivorous plants. Malathion and Acephate (Orthene) have also been reported as tolerable by carnivorous plants.

Although insects can be a problem, by far the biggest killer of carnivorous plants (besides human maltreatment) is grey mold (Botrytis cinerea). This thrives under warm, humid conditions and can be a real problem in winter. To some extent, temperate carnivorous plants can be protected from this pathogen by ensuring that they are kept cool and well ventilated in winter and that any dead leaves are removed promptly. If this fails, a fungicide is in order.

The easiest carnivorous plants for beginners are those from the cool temperate zone. These plants will do well under cool greenhouse conditions (minimum 5 °C in winter, maximum 25 °C in summer) if kept in wide trays of acidified or rain water during summer and kept moist during winter:

• Drosera capensis, the Cape sundew: attractive strap-leaved sundew, pink flowers, very tolerant of maltreatment.
• Drosera binata, the fork-leaved sundew: large, Y-shaped leaves.
• Sarracenia flava, the yellow trumpet pitcher: yellow, attractively veined leaves, yellow flowers in spring.
• Pinguicula grandiflora, the common butterwort: purple flowers in spring, hibernates as a bud (hibernaculum) in winter. Fully hardy.
• Pinguicula moranensis, the Mexican butterwort: pink flowers, non-carnivorous leaves in winter.

Venus flytraps will do well under these conditions but are actually rather difficult to grow: even if treated well, they will often succumb to grey mould in winter unless well ventilated. Some of the lowland Nepenthes are very easy to grow as long as they are provided with relatively constant, hot and humid conditions.